Ocean Visual Guide 2014 ed Fabien Cousteau

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6

FOREWORD BY FABIEN COUSTEAU

8

INTRODUCTION OCEAN WATER THE PROPERTIES OF WATER

28 30

THE CHEMISTRY OF SEAWATER

32

TEMPERATURE AND SALINITY

34

LIGHT AND SOUND

36

OCEAN GEOLOGY

38

THE FORMATION OF EARTH

40

THE ORIGIN OF OCEANS AND CONTINENTS

42

THE EVOLUTION OF THE OCEANS

44

TECTONICS AND THE OCEAN FLOOR

48 52

OCEAN WINDS

54

SURFACE CURRENTS

58

UNDERWATER CIRCULATION

60

THE GLOBAL WATER CYCLE

64

OCEANS AND CLIMATE

66

EL NIÑO AND LA NIÑA

68

HURRICANES AND TYPHOONS

70

WAVES AND TIDES

74

OCEAN WAVES

76

TIDES

78

Malhotra

EDITOR Himani Khatreja

MANAGING EDITOR

ABOUT THIS BOOK

CIRCULATION AND CLIMATE

DK UK SENIOR EDITOR Peter

CONTENTS

LONDON, NEW YORK, MELBOURNE, MUNICH, AND DELHI

OCEAN ENVIRONMENTS COASTS AND THE SEASHORE COASTS AND SEA-LEVEL CHANGE COASTAL LANDSCAPES BEACHES AND DUNES

86 88 92 106

ESTUARIES AND LAGOONS

114

SALT MARSHES AND TIDAL FLATS

124

MANGROVE SWAMPS

130

SHALLOW SEAS

138

OCEAN LIFE INTRODUCTION TO OCEAN LIFE

204

CLASSIFICATION

206

CYCLES OF LIFE AND ENERGY

BRYOZOANS

305

ECHINODERMS

306

SMALL, BOTTOM-LIVING PHYLA

313

PLANKTONIC PHYLA

317

212

TUNICATES AND LANCELETS

318

SWIMMING AND DRIFTING

214

JAWLESS FISHES

320

CONTINENTAL SHELVES

140

ROCKY SEABEDS

142

SANDY SEABEDS

144

BOTTOM LIVING

216

SHARKS, RAYS, AND CHIMAERAS

322

SEAGRASS BEDS AND KELP FORESTS

ZONES OF OCEAN LIFE

218

BONY FISHES

336

146

OCEAN MIGRATIONS

220

REPTILES

368

CORAL REEFS

152

LIVING DOWN DEEP

222

BIRDS

378

164

BIOLUMINESCENCE

224

MAMMALS

400

THE HISTORY OF OCEAN LIFE

226

THE PELAGIC ZONE THE OPEN OCEAN AND OCEAN FLOOR

166

KINGDOMS OF OCEAN LIFE

230

ZONES OF THE OPEN OCEAN

168

BACTERIA AND ARCHAEA

232

SEAMOUNTS AND GUYOTS

174

CHROMISTS

234

THE CONTINENTAL SLOPE AND RISE

176

OCEAN-FLOOR SEDIMENTS

180

ABYSSAL PLAINS, TRENCHES, AND MID-OCEAN RIDGES

182

VENTS AND SEEPS

188

THE POLAR OCEANS

190

ICE SHELVES

192

ICEBERGS

194

SEA ICE

198

POLAR OCEAN CIRCULATION

200

ATLAS OF THE OCEANS

BROWN SEAWEEDS

238

OCEANS OF THE WORLD

PLANT LIFE

242

THE ARCTIC OCEAN

424

RED SEAWEEDS

244

THE ATLANTIC OCEAN

428

GREEN SEAWEEDS

246

THE INDIAN OCEAN

446

GREEN ALGAE

248

THE PACIFIC OCEAN

456

MOSSES

249

THE SOUTHERN OCEAN

482

FLOWERING PLANTS

250

422

FUNGI

254

GLOSSARY

488

ANIMAL LIFE

256

INDEX

494

SPONGES

258

ACKNOWLEDGMENTS

510

CNIDARIANS

260

FLATWORMS

271

RIBBON WORMS

273

SEGMENTED WORMS

274

MOLLUSKS

276

ARTHROPODS

290

6

About this Book

Ocean Environments

THIS BOOK IS DIVIDED INTO

four chapters. An overview of the physical and chemical features of the oceans is given in the introduction; ocean environments looks at the main zones of the oceans, and ocean life examines the life-forms that inhabit them. The atlas of the oceans contains detailed maps of the oceans. Most chapters are divided into smaller sections.

This chapter looks at specific parts of the oceans. It is divided into sections on different zones, starting with coasts and the seashore and then moving to progressively deeper waters, first with shallow seas and then the open ocean and ocean floor. A final section, polar oceans, looks at the frozen waters around the North and South Poles. In each section, explanatory pages describe typical features and formative processes, while the succeeding pages contain profiles of actual features. The profiles are arranged by geographical location, starting with the Arctic Ocean and followed, in order, by the Atlantic, Pacific, Indian, and Southern Oceans. SHALLOW SEAS

160

PACIFIC OCEAN WEST

Shiraho Reef

TYPE

Fringing reef

10 square km (4 square miles)

AREA

Reasonable; damaged in parts by bleaching in 1998, 2007

CONDITION

Southeast coast of Ishigaki Island, at the CORAL REEFSLOCATION 153

SHALLOW SEAS

152

southwestern extremity of Japanese archipelago

CORAL DIVERSITY

Coral Reefs

Introduction

Reef Formation

In this seascape off a Fijian island, groups of shoaling sea goldies hover over diverse species of coral, sponges, and other reef organisms.

The individual animals that make up corals are called polyps. The polyps of the main group of reef-building corals, stony corals, secrete limestone, building on the substrate underneath. The polyps also form colonies that create community skeletons in a variety of shapes. An important contributor to the life of these corals is the presence within the polyps of tiny organisms called zooxanthellae, which provide much of the polyps’ nutritional needs. Other organisms that add their skeletal remains to the reef include mollusks and echinoderms. Grazing and boring organisms also contribute, by breaking coral skeletons into sand, which fills gaps in the developing reef. Algae and other encrusting organisms help bind the sand and coral fragments together. Most reefs do not grow continuously but experience spurts of growth interspersed with quieter periods, which are sometimes associated with recovery from storm damage.

CORAL REEFS ARE SOLID STRUCTURES

built from the remains of small marine organisms, principally a group of colony-forming animals called stony (or hard) corals. Reefs cover about 108,000 square miles (280,000 square km) of the world’s shallow marine areas, growing gradually as the organisms that form their living surfaces multiply, spread, and die, adding their limestone skeletons to the reef. Coral reefs are among the most complex and beautiful of Earth’s ecosystems, and are home to a fantastic variety of animals and other organisms; but they are also among the most heavily utilized and economically valuable. Today, the world’s reefs are under pressure from numerous threats to their health.

This opening chapter is divided into four sections. In ocean water, the properties of water itself are examined. ocean geology covers the materials of the ocean floor and the way that it changes over time. circulation and climate is about the interaction between oceans and the atmosphere and the large-scale movement of water, while tides and waves looks at movements and disturbances of water on a smaller scale.

Shiraho Reef, off Ishigaki Island, part of the Japanese archipelago, came to notice in the 1980s as an outstanding example of biodiversity, with some 120 species of coral and 300 fish

coral grows on shoreline, forming fringing reef

BARRIER REEF

Stony corals can grow only in clear, sunlit, shallow water where the temperature is at least 64˚F (18˚C), and preferably 77–84˚F (25–29˚C). They grow best where the average salinity of the water is 36 ppt (parts per thousand) and there is little wave action or sedimentation from river runoff. These conditions occur only in some tropical and subtropical areas.The highest concentration of coral reefs is found in the Indo-Pacific region, which stretches from the Red Sea to the central Pacific. A smaller concentration of reefs occurs around the Caribbean Sea. In addition to warm-water reefs, awareness is growing about other corals that do not depend on sunlight, and form deep, cold-water reefs—some of them outside the tropics (see p.178).

PACIFIC OCEAN WEST

Nusa Tenggara TYPE Fringing reefs, barrier reefs

BARRIER REEF

FRINGING REEF

5,000 square km (2,000 square miles)

Nusa Tenggara is a chain of around 500 coral-fringed islands in southern Indonesia. The northern islands are volcanic in origin, while the southern islands consist mainly of uplifted coral limestone. Many of the reefs have been only rarely explored. However, what surveys have been carried out

Damaged by fishing practices

CONDITION

Southern Indonesia, from Lombok in the west to Timor in the east

LOCATION

COLD-WATER CORAL

This species, Lophelia pertusa, is one of a few of the reef-forming corals that grow in cold water, at depths to 1,650 ft (500 m).

spread of volcanic ash and gases into rain clouds

THE OCEANS CONTAIN MILLIONS OF DISSOLVED chemical substances. Most of these are present in exceedingly small concentrations. Those present in significant concentrations include sea salt, which is not a single substance but a mixture of charged particles called ions. Other constituents include gases such as oxygen and carbon dioxide. One reason the oceans contain so many dissolved substances is that water is an excellent solvent.

The Salty Sea

salts are leached from rocks into rivers and streams and flow to ocean

The salt in the oceans exists in the form of charged particles, called ions, some positively charged and some negatively charged. The most common of these are sodium and chloride ions, the components of ordinary table salt (sodium chloride). Together they make up about 85 percent by mass of all the salt in the sea. Nearly all the rest is made up of the next four most common ions, which are sulfate, magnesium, calcium, and potassium. All these ions, together with several others present in smaller quantities, exist throughout the oceans in fixed proportions. Each is distributed extremely uniformly—this is in contrast to some other dissolved substances in seawater, which are unevenly distributed.

Shown here are various sources, sinks, and exchange processes for the ions, salts, and minerals (yellow arrows), gases (pink arrows), and plant nutrients (turquoise arrows) in seawater.

volcanic ash drifts down to sea

Gases in Seawater

KEY gases

This section covers the properties of the water molecule, the chemistry of seawater, and the way that attributes such as temperature, pressure, and light transmission change with depth in ocean water.

The main gases dissolved in seawater are nitrogen (N), oxygen (O2 ), and carbon dioxide (CO2). The levels of O2 and CO2 vary in response to the activities of photosynthesizing organisms (phytoplankton) and animals. The level of O2 is generally highest near the surface, where the gas is absorbed from the air and also produced by photosynthesizers. Its concentration drops to a minimum in a zone between about 660 ft (200 m) and 3,300 ft (1,000 m), where oxygen is consumed by bacterial oxidation of dead organic matter and by animals feeding on this matter. Deeper down, the O2 level increases again. CO2 levels are highest at depth and lowest at the surface, where the gas is taken up by photosynthesizers faster than it is produced by respiration.

ions, salts, and minerals plant nutrients

salt spray onto land

CARBON SINK

nutrients from soil wash into rivers and streams, and flow to ocean washing of ions from volcanic dust and gases into sea, dissolved in rain

Many marine animals, such as nautiluses (below), use carbonate (a compound of carbon and oxygen) in seawater to make their shells. After they die, the shells may form sediments and eventually rocks.

dust blown off land exchange of gases between ocean and atmosphere

exchange of gases between animals and seawater

OXYGEN PRODUCER AND CONSUMER

Oxygen levels in the upper ocean depend on the balance between its production by photo-synthesizing organisms, such as kelp, and its consumption by animals, such as fish.

BREAKDOWN OF SALT

If 2½ gallons (10 liters) of seawater are evaporated, about 123/4 oz (354 g) of salts are obtained, of the types shown below. 2½ gallons (10 liters) of seawater

Nutrients

other salts 1/4 oz (7.5g) calcium sulfate (gypsum) 2/3oz (17.7g) magnesium salts 2oz (54.8g) sodium chloride (halite) 10oz (274g)

+

– –

– Na+

–

–

– –

+

– +

+ +

+ +

+ Cl–

+

+

+ –

+ + –

– chloride ion (negative charge)

uptake of nutrients by phytoplankton

nutrient upwelling exchange of gases between phytoplankton and seawater

–

–

–

water molecule

–

PEOPLE

ALEXANDER MARCET The Swiss chemist and doctor Alexander Marcet (1770–1822) carried out some of the earliest research in marine chemistry. He is best known for his discovery, in 1819, that all the main chemical ions in seawater (such as sodium, chloride, and magnesium ions) are present in exactly the same proportions throughout the world’s oceans. The unchanging ratio between the ions holds true regardless of any variations in the salinity of water and is known today as the principle of constant proportions.

Sources and Sinks

sinking and

release of minerals from hydrothermal vents

decomposition The ions that make up the salt in the oceans have arrived of dead there through various processes. Some were dissolved out of organisms rocks on land by the action of rainwater and carried to the sea in rivers. Others entered the sea in the emanations of hydrothermal vents (see p.188), in dust blown off the land, or came from volcanic ash. There are also “sinks” for every type of ion—processes that remove them from seawater. These range from salt spray onto land to the precipitation of various ions onto the seafloor as mineral deposits. Each type of ion has a characteristic residence time. This is the time that an ion remains in seawater before it is removed. The common ions in seawater have long residence times, ranging from a few hundred years to hundreds of millions of years.

The Origin of Oceans and Continents

OCEAN GEOLOGY ▶

polar easterly

Ocean Winds

polar-front jet stream—narrow ribbon of strong wind at high altitude at top of front

THE PATTERN OF AIR MOVEMENT

over the oceans results from solar heating of the atmosphere and Earth’s rotation. This pattern of winds is modified by linked areas of low and high pressure (cyclones and anticyclones), which continually move over the oceans’ surface. Near coasts, additional onshore and offshore breezes are common. These are caused by differences in the capacity of sea and land to absorb heat.

The atmospheric cells cause north–south air movements. These are altered by the Coriolis effect. As the Earth spins, parcels of air at different latitudes in the atmosphere have different west-to-east velocities (air at the Equator moves fastest). When they change latitude by moving to the north or south, they retain these west-to-east velocities, which differ from those of air in the AIR DEFLECTIONS In the Northern Hemisphere, latitudes they move into. Hence, the air veers to the Coriolis effect causes all air movements to be the east (in the direction deflected to the right of of Earth’s spin) when their initial direction. In moving away from the the Southern Hemisphere, Equator and to the west they veer to the left. when moving toward it.

air deflected to right

air deflected to left

initial direction of air movement

westerlies

polar northeasterlies

westerlies

northeasterly monsoon (Nov–Mar)

northeasterly trade winds

Tropic of Cancer

equator

Tropic of Capricorn

top layer of upper mantle

bombardment gradually erased

THE EARLY EARTH mantle vigorous convection cells in upper mantle

The oceanic crust has a higher density than the continental crust, making it less buoyant. Both types of crust can be thought of as floating on the “plastic” upper mantle, and the oceanic crust lies lower due to its lower buoyancy. It is relatively thin, with a depth of never more than 7 miles (11 km), compared with a thickness of 15–43 miles (25–70 km) for most continental crust. It consists mainly of basalt, an igneous rock that is low in silica compared with continental rocks, and richer in calcium than the mantle. Basalt lava is created when hot material in the upper mantle is decompressed, allowing it to melt and form liquid magma. The decompression occurs beneath rifts in the crust, such as those found at the mid-ocean ridges, and it is through these rifts that lava is extruded onto the surface to create new ocean crust.

westerlies

volcanic eruptions add gases and water vapor to atmosphere

MANTLE ROCKS

ANDEAN VOLCANOES

This radar image shows volcanoes formed from andesite lava, whose composition is intermediate between oceanic and continental rocks.

55

This section describes the large-scale circulation of the oceans, both deep down and at the surface. It also looks at ocean climates and the many ways that the oceans and the atmosphere influence one another.

northeasterly trade wind

SATELLITE IMAGING

air ascends from cyclone air descends into anticyclone low pressure at center

central area of high pressure cold air sinks

Prevailing Winds The winds produced by pressure differences and modified by the Coriolis effect are called the prevailing winds. In the tropics and subtropics, the air movements toward the equator in Hadley cells are deflected to the west. These are known as trade winds. They comprise the northeasterly trades in the Northern Hemisphere, and southeasterly trades in the south. At higher latitudes, the surface winds in Ferrel cells deflect to the east, producing the westerlies. In the Southern Hemisphere, these winds blow from west to east without meeting land. Those around latitudes of 40˚S are known as the Roaring Forties. In polar regions, winds deflect to the west as they move away from the poles. These are known as polar northeasterlies and southeasterlies.

southwesterly monsoon (Apr–Oct)

Pressure-system Winds

warm air rising

ASCAT antenna (one of three)

prevailing cool local warm local cool

air spirals around central area of low pressure

air moving from high to low pressure deflected by Coriolis effect to form spiral

cold air flows toward area of low pressure

In any area of ocean where air sinks—often at subtropical latitudes—a zone of high atmospheric pressure, or anticyclone, develops. Where warm air rises, areas of low pressure, called cyclones or depressions, occur. These often develop near the equator and subpolar latitudes. Cyclones and anticyclones create linked, circulating wind patterns, which continually move and change. In the Northern Hemisphere, there is a clockwise movement of air around an anticyclone, and a counterclockwise motion CYCLONES AND ANTICYCLONES around a cyclone. This pattern is reversed in the Air moves from an area of Southern Hemisphere. Local pressure systems can affect high pressure toward one the general pattern of prevailing winds. In particular, of low pressure, but the cyclones move swiftly over the ocean and can produce Coriolis effect modifies this, producing circular winds. rapid changes in wind strength and direction. warm air cools at high altitude

BREEZY COAST

77

Ocean Waves

Wave Generation

WAVES ARE DISTURBANCES

in the ocean that transmit energy from one place to another. The most familiar types of waves—the ones that cause boats to bob up and down on the open sea and dissipate as breakers on beaches—are generated by wind on the ocean surface. Other wave types include tsunamis, which are often caused by underwater earthquakes (see p.49), and internal waves, which travel underwater between water masses. Tides (see p.78) are also a type of wave.

Wave Properties

direction of wave motion

TIDES AND WAVES ▶ trough

Wind energy is imparted to the sea surface through friction and pressure, causing waves. As the wind gains strength, the surface develops gradually from flat and smooth through growing levels of roughness. First, ripples form, then larger waves, called chop. The waves continue to build, their maximum size depending on three factors: wind speed, wind duration, and the area over which the wind is blowing, called the fetch. When waves are as large as they can get under the current conditions of wind speed and size of fetch, the sea surface is said to be “fully developed.” The overall state of a sea surface can be summarized by the significant wave height—defined as the average height of the highest one-third of the waves. For example, in a fully developed sea produced by winds of about 25 mph (40 kph), the significant wave height is typically about 8 ft (2.5 m).

wave height (amplitude)

disordered sea surface in fetch area

wind direction

ripples turn to chop

PHYLUM Mollusca

CLASSES 8

SPECIES 73,683

Anatomy Most mollusks have a head, a soft body mass, and a muscular foot. The foot is formed from the lower body surface and helps it to move. Mollusks have what is called a hydrostatic skeleton—their bodies are supported by internal fluid pressure rather than a hard skeleton. All mollusks have a mantle, a body layer that covers the upper body and may or may not secrete a shell. The shell of bivalves (clams and relatives) has two halves joined by a hinge; these can be held closed by powerful muscles while the tide is out, or if danger threatens. Mollusks other than bivalves have a rasping mouthpart, or radula, which is unique to mollusks. Cephalopods (octopuses, squid, and cuttlefish) also have beaklike jaws as well as tentacles, but most lack a shell, while most gastropods (slugs and snails) have a single shell. This is usually a spiral in snails, but can be cone-shaped in other forms, such as limpets.

color-coded panel shows position of group being described (indicated with white outline) in the classification hierarchy

gill

outside the fetch, waves become sorted by speed and wavelength

wave shortens in length and decreases in speed but increases in height

muscular foot

wave finally breaks

radula hinge ligament

BIVALVE ANATOMY

Bivalves are housed within a shell of two halves (right) from which the siphons and muscular foot can be extended. The shell is opened and closed by the adductor muscles, labeled in the body plan (far right).

CHOPPY SEA

In a choppy sea, the waves are 4–20 in (10–50 cm) high and have a wavelength of 10–40 ft (3–12 m).

direction of wave advance fetch (area over which wind blows)

wave reaches critical ratio of height to length and begins to break

water motion caused by the wave begins to interact with the sea bed and slow down

FULLY DEVELOPED ROUGH SEA

Wind speeds over 40 mph (60 kph) can generate very rough seas with waves more than 10 ft (3 m) high.

path of individual water particle

PARTICLE MOVEMENT

Wave Propagation Interference between two or more large waves occasionally causes a giant or “rogue” wave. This one, recorded in the Atlantic Ocean in 1986, had an estimated height of 56 ft (17 m). It broke over the ship pictured, bending its foremast back by 20˚.

eye SPIRAL SNAIL SHELL

water motion occurs offshore to depth of half the wavelength

GROUP INTRODUCTION ▶

BUILDING WAVES

ROGUE WAVES

mantle cavity

digestive system

These tiny waves are just a few millimetres high and have a wavelength of under 1½ in (4 cm).

SWELL

A swell is a series of large, evenly spaced waves, often observed hundreds of miles away from the storm that spawned them. Wavelengths range from tens to hundreds of feet.

SHOALING AND BREAKING

Shoaling occurs as waves enter shallow water. The wave length and speed both decrease, but the wave gains height. When the crest gets too steep, it curls and breaks.

HUMAN IMPACT

RIDING THE WAVES When a swell reaches a suitably shaped beach, it can produce excellent surfing conditions. Small spilling breakers are ideal for novice surfers, while experts seek out large plunging breakers that form a “tube” they can ride along. For tube-riding, the break of the wave must progress smoothly either to the right or left. Here, a surfer rides a rightbreaking wave in Hawaii— it is breaking from left to right behind the surfer.

Arrival on Shore As waves approach a shore, the motion they generate at depth begins to interact with the sea floor. This slows the waves down and causes the crests in a series of waves to bunch up—an effect called shoaling. The period of the waves does not change, but they gain height as the energy each contains is compressed into a shorter horizontal distance, and eventually break. There are two main types of breaker. Spilling breakers occur on flatter shores: their crests break and cascade down the front as they draw near the shore, dissipating energy gradually. In a plunging breaker, which occurs on steeper shores, the crest curls and falls over the front of the advancing wave, and the whole wave then collapses at once. Waves can also refract as they reach a coastline. This concentrates wave energy onto headlands (see p.93) and shapes some types of beach (see p.106). WAVE REFRACTION

When waves enter a bay enclosed by headlands, they are refracted (bent) as different parts of the wave-front encounter shallow water and slow down.

INTRODUCTION

In the fetch, many different groups of waves of varying wavelength are generated and interfere. As they disperse away from the fetch, the waves become more regularly sized and spaced. This is because the speed of a wave in open water is closely related to its wavelength. The different groups of waves move at different speeds and so are naturally sorted by wavelength: the largest, fastest-moving waves at the fore, the smaller, slower-moving ones behind. This produces a regular wave pattern, or swell. Occasionally, groups of waves from separate storms interfere to produce unusually large “rogue” waves. As they propagate across the open ocean, wind-generated waves maintain a constant speed, which is unaffected by depth until they reach shallow water. Only with waves of extremely long wavelength—tsunamis—is the speed of propagation affected by water depth.

water carried up shore in swash zone

Pages such as the ones shown here describe groups of organisms in general. All introductions contain an account of the defining physical characteristics, usually followed by further information on behavior, habitats, and classification.

REEF-DWELLING GOLIATH

The tropical giant clam is the largest bivalve and may measure more than 3 ft (1 m) across and weigh over 440 lb (220 kg).

GASTROPOD ANATOMY

spiral shell

sensory tentacle

direction of wave motion

Within the wave-generation area, the sea surface is usually quite confused—the result of groups of waves of different size and wavelength interfering with each other. Outside this area, the waves become sorted by speed to produce a more regular pattern, called a swell.

crest

As waves pass over the surface, the particles of water do not move forward with the waves. Instead, they gyrate in little circles or loops. Underwater, the particles move in ever-smaller loops. At a depth below about half the distance between crests, they are quite still.

AMONG THE MOST SUCCESSFUL of all marine animals, mollusks display great diversity and a remarkable range of body forms, allowing them to live almost everywhere from the ocean depths to the splash zone. They include oysters, sea slugs, and octopuses. Most species have shells SPECIES 73,683 and are passive or slow-moving; some lack eyes. Others are intelligent, active hunters with complex nervous systems and large eyes. Filter-feeding mollusks, such as clams, are crucial to coastal ecosystems, as they provide food for other animals and improve water quality and clarity. Many mollusks are commercially important for food, pearls, and their shells. DOMAIN Eucarya

KINGDOM Animalia

CAPILLARY WAVES (RIPPLES)

A group of waves consists of several crests separated by troughs. The height of the waves is called the amplitude, the distance between successive wave crests is known as the wavelength, and the time between successive wave crests is the period. Waves are classified into types based on their periods. They range from ripples, which have periods of less than 0.5 seconds, up to tsunamis and tides, whose periods are measured in minutes and hours (their wavelengths range from hundreds to thousands of miles). In between these extremes are chop and swell—the most familiar types of surface wave. Ocean waves behave like light rays: they are reflected or refracted by obstacles they encounter, such as islands. When different wave groups meet, they interfere—adding to, or canceling, each other. wavelength

PLUNGING BREAKER

“Barrel” or “tube-forming” breakers like this occur when the waves reaching shore have large amounts of energy. The seabed must be firm and quite steep.

ANIMAL LIFE

Mollusks

PHYLUM Mollusca CLASSES 8

DAY AND NIGHT

WAVES AND TIDES

still-water level

276

Land heats up faster

Local winds, called onshore and offshore than water during the day. air heats up Warm air rises over the land and rises over cool air breezes, are generated near coasts, especially in land drawn in and draws in cold air from sunny climes. Onshore breezes—sometimes the sea. At night, the land called sea breezes—develop during the day. cools more quickly, These are caused by the land heating up more reversing the airflow. quickly than the sea, as both absorb solar radiation. This occurs because the sea absorbs ONSHORE BREEZE large quantities of heat energy with only a small rise in temperature, whereas the same amount of heat energy is cold air sinks air heats up likely to cause the land temperature to rise sharply (see p.31). cool air drawn and rises As the land warms up, it heats the air above it, causing the air to rise. over ocean seaward Cooler air then blows in from the sea to take its place. In the evening, and at night, the opposite effect occurs. At nightfall, the land quickly cools down, but the sea remains warm and continues to heat the air above it. As this warm air rises, it sucks the cooler air off the land, and so generates an offshore breeze. This is sometimes called a “land breeze.” OFFSHORE BREEZE

On warm coasts, there is often a noticeable drop in temperature from midday as a cool sea breeze blows in off the water. The breeze typically reverses in the evening and at night.

76

The regular movements of the tides are described here, as well as the way that disturbances spread out across the surface in the form of waves.

cold air sinks

Coastal Breezes

PATTERN OF WINDS

Year-round, the winds over most oceans are trades or westerlies. An exception is the northern Indian Ocean—this has a monsoon climate, in which a seasonal switch in wind direction occurs.

This chapter contains two sections. The introduction to ocean life covers the ecology and history of marine life and the way that marine organisms are classified. It is followed by a larger section, kingdoms of ocean life. This is divided into domains or kingdoms and, in the case of the plant and animal kingdoms, further divided into smaller groups. In each case, a general overview of the organisms that make up the group is followed by profiles of a selection of individual species. The section begins with the smallest forms of life, the bacteria and archaea, and ends with the animal kingdom.

KINGDOM Animalia

◀ CIRCULATION AND CLIMATE

southeasterly trade wind

Ocean winds are monitored by instruments called scatterometers, such as an instrument called ASCAT on the METOP-A satellite (right). A scatterometer is a radar device that can measure both wind speed and direction.

REEF FLAT OFF PANTAR ISLAND

This shallow reef area, featuring numerous species of stony coral and a starfish, is in east Nusa Tenggara.

DOMAIN Eucarya

LONG-HAUL SAILING

trade winds meet at Intertropical Convergence Zone

prevailing warm

southeasterly trade winds

rifts occur when fragments of crust move apart

solid inner core

air rises at equator

air descends at pole

coral continues to grow where waves bring food

Winds can blow with a consistent strength and direction over large areas of ocean. Consequently, on long-haul sailing trips, the same basic sail settings can often be used for days on end.

air descends in subtropical latitudes

southeasterly trade winds

southeasterlies

Earth had deep oceans from an early stage, with volcanoes and an increasing area of continental crust standing above the surface. The ocean became salty as weathering of surface rocks added minerals to the water.

liquid outer core

volcanic activity adds igneous rocks to surface above rising flows

Peridotite is the dominant rock type found in the mantle, consisting of silicates of magnesium, iron, and other metals. Sometimes it is brought to the surface when parts of the ocean floor are uplifted, as here in Newfoundland, Canada, or as fragments from volcanic activity.

KEY

southeasterly trade winds

rivers erode and transport sediment

INTRODUCTION

INTRODUCTION

Intertropical Convergence Zone

westerlies

sedimentary rocks

During the process of differentiation, volatile materials were expelled from Earth’s interior by volcanic activity. The lightest gases, such as hydrogen and helium, would quickly have been lost to space, leaving a stable atmosphere of nitrogen, carbon dioxide, and water vapor. Some of the water vapor would have condensed to form liquid water, and it seems there was a significant ocean earlier than 4 billion years ago. Some meteorites contain 15-20 percent ocean water from water and the early Earth is thought volcanic eruptions and comet to have had the same composition, impacts providing an ample source for the early ocean. More water arrived with impacting comets. It was in the ocean that free oxygen first appeared, with the arrival traces of early of photo- synthesizing life around 3.5 billion years ago. meteorite and comet

primitive oceanic crust

DISCOVERY

The Coriolis Effect

crust pulled apart by convective motion in mantle

43

BANDED IRON

Known as a banded-iron formation, this layered rock contains iron oxides that formed as the oxygen content of early oceans increased.

Hadley cell

Solar heating causes the air in Earth’s atmosphere to CIRCULATION CELLS The atmospheric cells cycle around the globe in three sets of giant loops, produce north–south called atmospheric cells. Hadley cells are produced by airflows. These are modified by Earth’s warm air rising near the equator, cooling in the upper spin, producing winds atmosphere, and descending to the surface around that blow diagonally. subtropical latitudes (30˚N and S). Then the air moves subtropical back toward the equator. Ferrel cells are produced by jet stream air rising around subpolar latitudes (60˚N and S), cooling and falling in polar-front jet stream the subtropics, and then moving toward the poles. Polar cells are caused by air descending at the poles and moving toward the equator.

Earth’s rotation

air rises in subpolar latitudes Ferrel cell

southwesterly wind

primitive continental crust thickens above sinking mantle flow, without mantle interference

direction of Earth’s spin

Atmospheric Cells

initial direction of air movement

polar cell

Moho

OCEAN-FLOOR STRUCTURE

Three layers of basalt in the crust (basaltic lava, dikes, and gabbro) are separated from the mantle by the Mohorovicˇic´ discontinuity (the Moho). The top layer of the upper mantle is fused to the base of the crust to form the rigid lithosphere, which makes up tectonic plates.The asthenosphere is the soft zone over which the plates of the lithosphere glide.

INTRODUCTION

CIRCULATION AND CLIMATE

ocean crust

lithosphere

magma rises to surface

basalt continuously intrudes from mantle

ZIRCON

Water and Atmosphere

Oceanic Crust

ocean surface

peridotite

INTRODUCTION

54

basalt sheets (dikes) sediment

gabbro

asthenosphere

central area filled by reef limestone

Ocean Life greenstone belts above rising mantle flow

zircon crystals, among the earliest continental crust materials

Continental Crust The continents include a wide range of rock THE OLDEST ROCKS types, including granitic igneous rocks, sedimentary These sedimentary rocks on Baffin Island rocks, and the metamorphic rocks formed by the lie on the Canadian alteration of both. They contain a lot of quartz, a Shield. The stable mineral absent in oceanic crust. The first continental continental shields rocks were the result of repeated melting, cooling, contain the world’s most ancient rocks, and remixing of oceanic crust, driven by volcanic activity above mantle convection cells, which were which are around 4 billion years old. much more numerous and vigorous than today’s. Each cycle left more of the heavier components in the upper mantle and concentrated more of the lighter components in the crust. The first microcontinents grew as lighter fragments of crust collided and fused. Thickening of the crust led to melting at its base and underplating with granitic igneous rocks. Weathering accelerated the process of continental rock formation, retaining the most resistant components, such as quartz, while washing solubles into the ocean. rift

volcanic island becomes submerged

These pages describe general types of environments. The example above is taken from the SHALLOW SEAS section.

THE ORIGIN OF OCEANS AND CONTINENTS DEVELOPMENT OF CONTINENTAL CRUST

Modification of the crust above rising mantle flows was delayed by the continuous intrusion of mantle basalt, resulting in the greenstone belts found today at the heart of each continental shield.

EARTH’S OCEANS FORMED MORE THAN 4 billion years ago, mainly from water vapor that condensed from its primitive atmosphere but also from water brought from space by comets. Initially, after acquiring a layered internal structure, the Earth had a uniform crust that was enriched in lighter elements and floated on an upper mantle made of denser materials. Later, the crust became differentiated into two types as continents began to form, made from rocks that were chemically distinct from those underlying the oceans.

basaltic lava

Bleaching refers to color loss in reef-building corals and occurs when the tiny organisms called zooxanthellae, which give corals their colors, are ejected from coral polyps or lose their pigment. In extreme cases, this can lead to the coral’s death.Various stresses can cause bleaching, including pollution, ocean temperature rise, and ocean acidification (see p.67). In recent decades, some mass bleaching events have affected reefs over wide areas.

coral continues to grow, forming barrier reef

INTRODUCTION

As well as describing the composition of the ocean floor, this section looks at the processes that shape it, tracing the origin of the oceans and their changing size and shape over geological time.

ATOLL

This satellite image of the Skagerrak (a strait linking the North and Baltic seas) shows a bloom of phytoplankton, visible as a turquoise discoloration in the water.

These tiny forms of planktonic organisms have cell walls made of silicate. They can only grow if there are sufficient amounts of silica present in the water.

OCEAN GEOLOGY

42

An atoll is shown here forming around a volcanic island. First, the island’s shore is colonized by corals forming a fringing reef (above). Over time, the island subsides, but coral growth continues, forming a barrier reef (above right). Finally, the island disappears, but the coral maintains growth, forming an atoll (right). Atolls can also form as a result of sea-level rise.

reef face

▲ EXPLANATORY PAGES

SILICEOUS DIATOMS

RIVER DISCHARGE

River discharge is a mechanism by which ions of sea salt and nutrients enter the oceans. Here, the Noosa River empties into the sea on the coast of Queensland, Australia.

CORAL BLEACHING

lagoon of shallow water

ATOLL FORMATION

PLANKTON BLOOM

dissolving of minerals from sea floor precipitation of minerals onto sea floor carbonates incorporated into seafloor sediments from animal shells

INTRODUCTION

INTRODUCTION

slow uplift of sedimentary rocks at continental margins, exposing salts, minerals, and ions at surface

–

sodium chloride crystal

Numerous substances present in small amounts in seawater are essential for marine organisms to grow. At the base of the oceanic food chain are phytoplankton—microscopic floating life-forms that obtain energy by photosynthesis. Phytoplankton need substances such as nitrates, iron, and phosphates in order to grow and multiply. If the supply of these nutrients dries up, their growth stops; conversely, blooms (rapid growth phases) occur if it increases. Although the sea receives some input of nutrients from sources such as rivers, the main supply comes from a continuous cycle within the ocean. As organisms die, they sink to the ocean floor, where their tissues decompose and release nutrients. Upwelling of seawater from the ocean floor (see p.60) recharges the surface waters with vital substances, where they are taken up by the phytoplankton, refueling the chain.

sodium ion (positive charge)

+

+

+

WATER AS A SOLVENT

The charge imbalance on its molecules makes water a good solvent. When dissolving and holding sodium chloride in solution, the positive ends of the molecules face the chloride ions and the negative ends face the sodium ions.

◀ OCEAN WATER

lagoon volcanic island

The body plan (far left) of gastropods (slugs and snails) features a head, large foot, and usually a spiral shell (left). In shelled forms, all the soft body parts can be withdrawn into the shell for protection, or to conserve moisture while uncovered by the outgoing tide.

shell mantle cavity

digestive system

siphon

muscular foot BIVALVE SHELL gill

adductor muscle

jaws feeding arm

radula

OCEAN LIFE

The Chemistry of Seawater

SOURCES, SINKS, AND EXCHANGES

33

OCEAN ENVIRONMENTS

THE CHEMISTRY OF SEAWATER

OCEAN ENVIRONMENTS

OCEAN WATER

OCEAN ENVIRONMENTS

HUMAN IMPACT

32

digestive system

eye arm

internal shell

siphon gill

mantle cavity

TYPE

Atol

330 (130 squar

AREA

CONDITION

recovering bleaching Central Sulu Sea, between t and northern Borneo

LOCATION

The Tubbataha Reefs lie arou atolls in the centre of the Sul are famous for the many larg (open ocean) marine animals to them – such as sharks, Ma turtles, and barracuda. The ste shelving reefs here are also ri smaller life, including many s of crustaceans, colourful nud (sea slugs), and more than 35 of stony and soft coral. In the early 1990s, the Tub Reefs were rated by scuba di among the top ten dive sites world. However, during the they suffered considerable da from destructive fishing pract the establishment of a seawee In this photograph of a steeply she reef slope, several species of soft are visible, together with a shoal o Longfin Bannerfish.

AREA

The conditions needed for the growth of warm-water coral reefs are found mainly within tropical areas of the Indian, Pacific, and Atlantic oceans. The reefs are chiefly in the western parts of these oceans, where the waters are warmer than in the eastern areas.

An atoll is a ring of coral reefs or coral islands enclosing a central lagoon. It may be elliptical or irregular in shape.

island subsides when volcano has become inactive

PACIFIC OCEAN WEST

Tubbataha Reefs

CORAL DROP-OFF

Distribution of Reefs

ATOLL

A barrier reef is separated from the coast by a lagoon. In this aerial view, the light blue area is the reef and the distant dark blue area is the lagoon.

sea level

Despite its name, the colour of this coral varies from violet through blue, turquoise, and green to yellow-brown. Its branching vertical plates can form massive colonies.

This group of branching hard corals is growing at a depth of about 16 ft (5 m) off the coast of eastern Indonesia. Individual stony corals can grow up to a few inches per year.

OPEN POLYPS

At the center of each polyp is an opening, the mouth, which leads to an internal gut. The tissue around the gut secretes limestone, which builds the reef.

WARM-WATER REEF AREAS

A fringing reef directly borders the shore of an island or large landmass, with no deep lagoon.

BLUE RIDGE CORAL

STONY CORAL

Types of Reefs Coral reefs fall into three main types: fringing reefs, barrier reefs, and atolls. The most common are fringing reefs. These occur adjacent to land, with little or no separation from the shore, and develop through upward growth of reef-forming corals on an area of continental shelf. Barrier reefs are broader and separated from land by a stretch of water, called a lagoon, that can be many miles wide and dozens of yards deep. Atolls are large, ring-shaped reefs, enclosing a central lagoon; most atolls are found well away from large landmasses, such as in the South Pacific. Parts of the reef structure in both atolls and barrier reefs often protrude above sea level as low-lying coral islands—these develop as wave action deposits coral fragments broken off from the reef itself. Two other types of reefs are patch reefs—small structures found within the lagoons of other reef types—and bank reefs, comprising various reef structures that have no obvious link to a coastline.

FRINGING REEF

species concentrated in a few square kilometres. The reef also contains the world’s largest colony of rare Blue Ridge Coral (Heliopora coerulea). For decades, environmentalists battled to save the reef from the building of a new airport for Ishigaki. A proposal to construct the airport on top of the reef was dropped, but concern remains now that it has been built on land, as discharge of excavated soil into the reef is likely to have an adverse effect.

CEPHALOPOD ANATOMY

Cephalopods have large eyes, in front of which there are a number of tentacles. The siphon functions in respiration and in rapid movement. Some forms have a flattened internal shell.

indicate an extremely high d marine life in this region. Fo a single large reef can contai than 1,200 species of fish (m in all the seas in Europe com and 500 different species of building coral. Common ani include Eagle Rays, Manta R

7

Atlas of the Oceans PACIFIC OCEAN SOUTHWEST

Great Barrier Reef TYPE

map shows location and, in most profiles, geographical extent of feature

Barrier reef table of summary information (categories vary between sections)

14,300 square miles (37,000 square km) AREA

CONDITION Damaged by Crown-of-thorns Starfish; coral bleaching

Parallel to Queensland coast, northeastern Australia

LOCATION

Parallel to Queensland coast, northeastern Australia

LOCATION

A

HABITAT

Middle and lower rocky shores

Caribbean, Bahamas, Florida

DISTRIBUTION

Northwestern and northeastern

Atlantic

OCEAN LIFE

One of the most common rocky shore gastropods, the dog whelk has a thick, heavy, sharply pointed spiral shell. The shell’s exact shape depends on its exposure to wave action, and its color depends on diet. Dog whelks are voracious predators, feeding mainly on barnacles and mussels. Once the prey has been located, the whelk uses its radula to bore a hole in the shell of its prey before sucking out the flesh.

Sense Organs

PIGMENTED SKIN CELLS HELP CUTTLEFISH TO CHANGE COLOR

When the cuttlefish passes over a darker background, it disperses the colored pigments throughout each of its chromatophores, and the animal darkens.

2

MOLLUSCAN BEAUTY

Displaying fabulous warning colors, this nudibranch is a shell-less example of the many thousands of marine species of gastropods (slugs and snails).

K

il ur

re eT

nc

33m (108ft)

B

1,857m (6,093ft)

Bowers Attu Attu Near Basin Island Islands Agattu Island

e

u

DISTRIBUTION

HIDING FROM VIEW There are times when the Venus comb buries itself just below the surface of the sea floor, displacing the sand with movements of its muscular foot. However, it leaves the opening of its tubular inhalant siphon above the sand’s surface so that it can draw water into its mantle cavity to obtain oxygen and to “taste” the water for the presence of prey.

CLASS GASTROPODA

Giant Triton Charonia tritonis LENGTH

Up to 16 in (40 cm) HABITAT

Coral reefs, mostly in subtidal zones

DISTRIBUTION

Indian Ocean, western and central

Pacific

CLASS GASTROPODA

HALF BURIED

The spines of this Venus comb can be seen sticking out of the sand. The siphon is visible to the right of the picture.

Common Periwinkle Littorina littorea CLASS GASTROPODA

Flamingo Tongue LENGTH

1–11/2 in (3–4 cm) HABITAT

Western Atlantic, from North Carolina to Brazil; Gulf of Mexico, Caribbean Sea

277

The off-white shell of the flamingo tongue cowrie is usually almost completely hidden by the two fleshy, leopard-spotted extensions of its

body’s outer casing, or mantle. When threatened, however, its distinctive coloration quickly disappears as it withdraws all its soft body parts into its shell for protection. This snail feeds almost exclusively on gorgonian corals, which dominate Caribbean reef communities. Although these corals release chemical defenses to repulse predators, the flamingo tongue cowrie is apparently able to degrade these bioactive compounds and eat the corals without coming to any harm. After mating, the female strips part of a soft coral branch and deposits the egg capsules on it. Each capsule contains a single egg that will hatch into a free-swimming planktonic larva.

LENGTH

Up to 1 in (3 cm) HABITAT

Upper shore to sublittoral rocky shores, mud flats, estuaries Coastal waters of northwest Europe; introduced to North America

DISTRIBUTION

This gastropod is one of the very few animals that eats the crown-of-thorns starfish, itself a voracious predator and destroyer of coral reefs. The giant triton is an active hunter that will chase prey, such as starfish, mollusks, and sea stars, once it has detected them. It uses its muscular single foot to hold its victim down while it cuts through any protective covering using its serrated, tonguelike radula; it then releases paralyzing saliva into the body before eating the subdued prey. directly into the water during the spring tides. The eggs hatch into free-swimming larvae that float in the plankton for up to six weeks. After settling and metamorphosing into the adult form, it takes a further two to three years for the adult to fully mature. It feeds mainly on algae, which it rasps from the rocks. In the 19th century, the common periwinkle was accidentally introduced into North America, where its selective grazing of fast-growing algal species has considerably affected the ecology of some rocky shores.

The common periwinkle has a black to dark gray, sharply conical shell and slightly flattened tentacles, which in juveniles also have conspicuous black banding. The sexes are separate and fertilization occurs internally. Females release egg capsules, containing two or three eggs,

◀ SPECIES PROFILES

GRAFTING OYSTERS

All species profiles contain a text description and, in most cases, a color photograph and distribution map.

Pearls form in oysters when a grain of sand or other irritant lodges in their shells. The oyster coats the grain with a substance called nacre, forming a pearl. Today many pearls are cultured artificially: the shell is opened just enough to introduce an irritant into the mantle cavity.

CLASS GASTROPODA

Flamingo Tongue

Movement Mollusks move in many different ways. Most gastropods glide across surfaces using their mucus-lubricated foot. Exceptions include the sea butterfly, which has a modified foot with finlike extensions for swimming. Some bivalves, such as scallops, also swim, producing jerky movements by clapping the two halves of their shell together. Other bivalves burrow by probing with their foot and then pulling themselves downward by muscular action. Cephalopods are efficient swimmers; some have fins on the sides of their bodies that let them hover in the water, and they can accelerate rapidly by squirting water out through their siphons.

Cyphoma gibbosum LENGTH

1–11/2 in (3–4 cm)

name of group to which species belongs common name of species is followed by scientific name

HABITAT

Coral reefs at about 50 ft (15 m)

AIDED BY MUCUS

Muscular contractions ripple through the fleshy foot of this marine snail. It secretes a lubricating mucus that helps it to move on rough surfaces.

Respiration Most mollusks obtain oxygen from water using gills, called ctenidia, which are situated in the mantle cavity. These are delicate structures with an extensive capillary network and a large surface area for gaseous exchange. In species that are always submerged, water can continually be drawn in and over the gills. Those living in the intertidal zone are exposed to the air for short periods and must keep their gills moist. At low tide, bivalves clamp shut and some gastropods close their shell with a “door” (called an operculum) to retain moisture. Pulmonate snails have a simple lung formed from the mantle cavity instead of ctenidia and are mostly terrestrial but others live on the seashore and can absorb oxygen through their skin when immersed.The respiratory pigment in most molluscan blood is a copper compound called hemocyanin. It is not as efficient at taking up oxygen as external gills hemoglobin and gives mollusks’ (ctenidia) blood a blue color.

Nudibranchs (sea slugs) have feathery external gills toward the rear of their bodies. The warning coloration of this species includes the bright orange gills.

DISTRIBUTION Western Atlantic, from North Carolina to Brazil; Gulf of Mexico, Caribbean Sea

OCEAN LIFE

COLOR CODING

en

Riv er

Yuk on

Riv kw im

ko

Ra t I sla nd s

Kiska Island Amchitka Island

ch

20m (66ft)

Inlet

K

Cook

rai t

a Pe

ni

ns

f ko

St

Tanaga A Island

ds leutian Islan Atka Island

Atka

n

Ale

Isla Fox

E

Po r B a tl oc nk k

Kodiak

Kodiak Island

i

Tr

en

ch

Gulf of Alaska

Patton Seamount Patt on

Seamou nts

Murray Seamount Gilbert Seamount

G i lb er

Parker Seamount

5,267m (17,281ft)

160˚W

F

ut

an

G

2

sea depth maximum depth on map

Chichagof Admiralty Island Island 295m A Sitka (968ft) 3,640m Baranof (11,943ft) Island Ketchikan of Alask a Seamount Pr ovinc Prince of e Gulf Pratt Wales Quinn Seamount Prince Rupert Island n Giacomini Seamount Durgin o ce Seamount Dixtran Seamount K Cape En o Surveyor Seamdiak Knox Seamount ount Dickins s Welker Seamount

Shumagin Islands

so Dutch Davidnk Umnak Harbor Ba Island Unalaska nds Island

Juneau

Glacier Bay

Port Moller Unimak Island False Pass

7,314m 170˚W (23,997ft)

D

Bristol Bay 62m (203ft)

ul

Cape Constantine

Umnak Be Plateau ring Cany on

Andreano f Islands

180˚

C

Cape Newenham

Pribilof Islands

6,102m (20,021ft)

Shuyak Island

li

Bering Sea

11m (36ft) Bowers Bank

Homer

seamount

Yakutat

Prince Cape William Saint Elias Sound

tectonic plate boundary

Gibson Seamount

150˚W

H

Seamount

Denson Seamount

Alaska Plain

White Marsh Seamount

t Se a

mo

Schoppe

un

I

Ridge

Peters

ts

766m (2,513ft)

e en

Ch a

rlo t Bowie te Seamount Oshawa Seamount

Miller Seamount

Ridge

140˚W

Isla n

3

213m

t (699ft) Cape St.James QueenCharlotte Sound Cape Scott

ds

Explorer Seamount

130˚W

J

K

50˚N

rait of

Vancouve r

Vancouver

G Island eorgia

Victoria Strait of Seattle Juan de Fuca

4

UNITED STATES OF AMERICA

Cascadia Basin L

John Sparks is a curator in the Department of Ichthyology at the American Museum of Natural History and an adjunct professor at Columbia University in New York City. The revised edition was prepared with the help of Mark Siddall, a curator in the Division of Invertebrate Zoology and a professor at the Richard Gilder Graduate School at the American Museum of Natural History.

Indian Ocean, western Pacific

One of the largest cowrie species, the tiger cowrie has a shiny, smooth, domed shell with a long, narrow aperture, and is variously mottled in black, brown, cream, and orange. The cowrie’s mantle (its body’s outer, enclosing layer) can extend to cover parts of the exterior of the shell. These extensions have numerous projections, or papillae, whose exact function is unknown, but which may increase the surface area for oxygen absorption or provide camouflage of some sort. Tiger cowries are nocturnal creatures, hiding in crevices among the coral during the day and emerging at night to graze on algae. The sexes are separate and fertilization occurs internally. Females exhibit some parental care in that they protect their egg capsules by covering them with their muscular foot until they hatch into larvae, which then enter the plankton to mature.

DISTRIBUTION

Swimming backward reduces drag from the tentacles. The siphon, used for jet propulsion, is clearly visible in this Humboldt squid.

Tr

20m (66ft)

ai la en insu Seward n Pe

CONSULTANTS

Low tide to 100 ft (30 m) on coral reefs and flats

Cyphoma gibbosum

siphon

Takoma Reef

an

170˚E

HABITAT

Coral reefs at about 50 ft (15 m)

REDUCING DRAG

ti

16,400 ft (5,000 m)

it Kuskokwim Bay

Nunivak Island

4,024m (13,203ft) Ulm Bowers Seamount Plateau

A

Northwest Pacific Basin

160˚E

Aleutian Basin

Komandorskiye Ostrova

Ostrov Mednyy

6,088m (19,975ft)

4

Pervenets Canyon

land

Cordova

S he

h

LENGTH

SEEDING AN OYSTER

The giant cuttlefish’s color change is due to skin cells called chromatophores. It is pale when pigment is confined to a small area of each cell.

˚N

Mednyy Seamount

9,800 ft (3,000 m)

C A N A D A

Anchorage

Et

Up to 6 in (15 cm)

The best-shaped artificial pearls are produced by “seeding” oysters with a tiny pearl bead and a piece of mantle tissue from another mollusk .

1

50

635m (2,083ft)

er

s Ku

Hooper Bay Saint Matthew Island

285

HUMAN IMPACT

Touch, smell, taste, and vision are well developed in many mollusks. The nervous system has several paired bundles of nervous tissue (ganglia), some of which operate the foot, and interpret sensory information such as light intensity. Photoreceptors range from the simple eyes (ocelli) seen along the edges of the mantle or on bivalve siphons, to the sophisticated image-forming eyes of cephalopods. Cephalopods are also capable of rapidly changing their color.

cha e

Mys Kam rr ac 7,864m Shipunskiy Te (25,802ft) 3

29m (95ft)

Mys Olyutorskiy

CLASS GASTROPODA

three to five clearly visible holes in the shell, through which water flows for respiration.These are filled and replaced with new holes as the abalone increases in size. Sea otters are one of the red abalone’s main predators, along with human divers.

MOLLUSKS

Kamchatskiy Zaliv Ostrov Beringa Petropavlovsk- Kronotskiy Kamchatskiy Zaliv tka

12m (39ft)

Olyutorskiy Zaliv

Tiger Cowrie

OCEAN LIFE

The small, rounded, smooth, blackand-white striped shell of the zebra nerite is typical of the species, but in examples from Florida the shell is sometimes more mottled or speckled with black. These gastropods are most active during the day, when they feed on microorganisms such as diatoms and cyanobacteria, but if they become too hot or they are exposed at low tide, they cluster together, withdraw into their shells, and become inactive. This may be a mechanism for preventing excessive water loss. Unusually for gastropods, there are separate males and females of zebra nerites and fertilization of the eggs occurs internally. The males use their penis to deposit sperm into a special storage organ inside the female. Later, she lays a series of small white eggs that hatch into planktonic larvae.

li v y Za i ns k Ostrov Karaginskiy

Kamchatka Basin Mys Sivuchiy

shaded area of map shows known natural range of species

table of summary information (varies between categories) all distribution maps are accompanied by a written summary of the range of the species

CONTRIBUTORS Richard Beatty Glossary Kim Bryan Introduction to Ocean Life, Bacteria and Archaea, Protists, Fungi, Mollusks, Arthropods, Red Crab Migration David Burnie Animal Life, Reptiles, Birds, Mammals Robert Dinwiddie Ocean Water, Circulation and Climate, Tides and Waves, Coasts and the Seashore, Shallow Seas, Polar Oceans, Ocean Yacht Racing, Shutting Down the Atlantic Conveyor, Hurricane Katrina, Global Warming and Sea-level Rise, Coastal Defenses, The Titanic Disaster Frances Dipper Introduction to Ocean Life, Sponges, Cnidarians, Segmented Worms, Flatworms, Ribbon Worms, Bryozoans, Echinoderms, Small Bottom-living Phyla, Planktonic Phyla, Tunicates and Lancelets, Jawless Fishes, Cartilaginous Fishes, Bony Fishes Philip Eales Ocean Geology, Atlas of the Oceans, Oceanography from Space, The Indian Ocean Tsunami, Ice-shelf Breakup Monty Halls Diving Tourism Sue Scott Shallow Seas, Red and Brown Seaweeds, Plant Life, Green Seaweeds, Green Algae, Mosses, Flowering Plants, Fishing Michael Scott The Open Ocean and Ocean Floor, Exploration with Submersibles, Cold Water Reefs, Biodiversity Hotspots, Whale Migration, Wind Farming in the Baltic The revised edition was prepared with the help of David Burnie (Ocean Life), Robert Dinwiddie (Introduction and Ocean Environments), Frances Dipper (Ocean Life), and Philip Eales (Atlas of the Oceans)

AT L A S O F T H E O C E A N S

LENGTH

Up to 2 1/2 in (6 cm)

HABITAT

rag

St

DISTRIBUTION

LENGTH

Up to 1/2 in (1 cm) Rocky tide pools

Pacific

The tropical carnivorous snail known as the Venus comb has a unique and spectacular shell. There are rows of long, thin spines along its longitudinal ridges, which continue onto the narrow, rodlike, and very elongated siphon canal. The exact function of these spines is unknown, but they are thought to be either for protection or to prevent the snail from sinking into the soft substrate on which it lives. Its body is tall and columnar so that it can lift its cumbersome shell above the sediment to move in search of food.

Ka

tk a

Qu

Nucella lapillus

a

cha

1,600 ft (500 m)

6,500 ft (2,000 m)

go

Dog Whelk

Puperita pupa

Eastern Indian Ocean and western

s ul

Ka m

1

800 ft (250 m)

500 miles

3,300 ft (1,000 m)

ai Str cate He

Zebra Nerite

DISTRIBUTION

nin

sea level

400

˚N 60

el a

CLASS GASTROPODA

e aP

Ust’-Kamchatsk

110˚W

500 km

300

ip

Tropical warm waters to 650 ft (200 m) CLASS GASTROPODA

at k

400

200

r ch

HABITAT

ch

Norton Sound

300

100

A

LENGTH

Up to 3 in (8 cm)

2

Saint Lawrence Island

Mys Navarin

Nome Norton Plain

Khatyrka Ossora

Cypraea tigris

HABITAT

Venus Comb

L

KEY 200

100

0

er

Easily distinguished from most other gastropods by the conical shape of its spiral shell, the top shell moves slowly over reef flats and coral rubble, feeding on algae. Demand for its flesh and pretty shell has led to declining numbers, especially in the Philippines, due to unregulated harvesting. It has, however, been successfully introduced elsewhere in the Indo-Pacific, such as French Polynesia and the Cook Islands, from where some original sites are being restocked.

LENGTH

Murex pecten

K 120˚W

SCALE

nd

Reef fish, including Longfin Bannerfish, Milletseed Butterflyfish, and Bluestripe Snappers, swim around a table coral.

6–8 in (15–20 cm)

CLASS GASTROPODA

RETURNING HOME

J 130˚W

140˚W

UNITED STATES OF A MERICA

a

FRENCH FRIGATE SHOALS

Rocks from low tide mark to 100 ft (30 m)

Limpets gradually grind a “scar” into their anchor spot on the rock, to aid their grip and help retain water. A mucus trail leads them back to the spot.

I Arctic Circle

0

Chirikof Basin

Mys Chukotskiy

Sea of Okhotsk

In most cases, explanatory pages are followed by profiles of actual features. For example, the profiles shown here describe coral reefs from around the world. Most profiles are illustrated with color photographs.

Haliotis rufescens

The largest of the abalone species, the red abalone is so called because of the brick-red color of its thick, roughly oval shell. There is an arc of

Fuca Plate west of Vancouver Island. The seamounts were created above the hotspot over the last 30 million years, then carried northwest by seafloor spreading. Since 1977, oil has been shipped through ports on the south coast of Alaska. In 1989, Prince William Sound was the site of one of the worst maritime environmental disasters, when the tanker Exxon Valdez ran aground, releasing about 30 million gallons (114 million liters) of crude oil.

were born. The floor of the Gulf of Alaska is peppered with seamounts. There are two main chains: the Patton and Gilbert seamounts, and the Kodiak Seamounts, both running away from the Alaska Peninsula. Their origin is the Cobb Hotspot, situated beneath the spreading center of the Juan de

H 150˚W

160˚W

sk

A wide fringing reef almost completely surrounds the shoreline of mountainous Moorea, part of which is visible in this view.

Red Abalone

East Pacific coasts from southern Oregon, US to Baja California, Mexico

G Good Bayhop

Seward Peninsula

la

MOOREA

CLASS GASTROPODA

DISTRIBUTION

ALASKAN FJORD

The valleys and fjords of the Alexander Archipelago testify to extensive erosion by glaciers during the last ice age.

xa

Eastern Indian Ocean, western and southern Pacific

DISTRIBUTION

The Cascadia Basin is the last remnant of the original eastern Pacific oceanic plate, the Farallon Plate, which has been almost entirely subducted beneath North America. The Cascade Range of volcanoes in Oregon and Washington State, including Mount St. Helens, are a product of this subduction. Mount St. Helens erupted in a catastrophic explosion in 1982, killing 57 people, and still shows signs of activity. Earthquakes and associated tsunamis are also a risk in the area, although the last major earthquake is thought to have been in 1700. The underlying ocean crust appears to be split into three small plates. The largest is the Juan de Fuca Plate, named after a Greek sea captain who explored the area for Spain in 1592. The Explorer Plate lies to the north and the Gorda Plate to the south.

le

The common limpet’s muscular foot, seen here from below, holds it firmly to its rock, regardless of the strength of the waves.

taller shells allow for better water retention during periods of exposure. Limpets travel slowly during low tide, covering up to 24 in (60 cm) using contractions of their single foot. They graze on algae from rocks using a radula (a rasplike structure), which has teeth reinforced with iron minerals.

Pacific Ocean; Columbia, Fraser rivers

INFLOWS

A counterclockwise subpolar gyre extends across the north Pacific and into the Gulf of Alaska, fed by the warm waters of the northern Kuroshio Extension, the extension of the Kuroshio Current. The surface waters are cooled and become less saline due to precipitation as they cross the ocean. Many of the storms that lash the west coast of Canada originate in the Gulf of Alaska. The circulation is completed as the Alaska Current and the Aleutian Current return west along the Alaskan coast and south of the Aleutian Islands. The gulf ’s waters are very productive, providing feeding grounds for many species of fish. Pacific salmon spend up to five years at sea, much of it in the gulf and adjacent seas, before returning to spawn in the Asian and North American rivers where they

a Str

Abundant on rocks from the high to the low water mark, the common limpet is superbly adapted to shore life. A conical shell protects it from predators and the elements. Limpets living at the low water mark are buffeted by the waves and so require smaller, flatter shells than those living at the high water mark, where wider,

9,600 ft (2,930 m)

INFLOWS

n oli

Northeastern Atlantic from Arctic Circle to Portugal

DISTRIBUTION

66,000 sq. miles (170,000 sq. km)

MAXIMUM DEPTH

A

◀ FEATURE PROFILES

Gulf of Anadyr

idge rs R we Bo

Intertidal and shallow subtidal areas, reef flats to 23 ft (7 m)

R US S I AN F EDER ATI ON

ti

HABITAT

conical shell

MUSCULAR FOOT

F 170˚W

Chukchi Sea Chukotskiy Poluostrov

Anadyr’

se l A n Ri a

6 in (16 cm)

HABITAT

E Arctic Circle

180˚

dy r’

eu

LENGTH

DIAMETER

21/2 in (6 cm) Rocks on high shore to sublittoral zone

D 170˚E

160˚E

150˚E

Stra it

˚N

ing

60

Al

CLASS GASTROPODA

Top Shell Tectus niloticus

THE BERING STRAIT

This satellite image shows ice from the Chukchi Sea streaming south through the Bering Strait.

C

1

MOLLUSKS orange foot with greenish tint

CLASS GASTROPODA

Common Limpet

AREA

16,400 ft (5,000 m)

Susitna, Copper rivers; icebergs from numerous glaciers

B er

The Society Islands comprise a chain of volcanic and coral islands in the South Pacific, including islands with barrier reefs (such as Rai’atea), islands with both fringing and barrier reefs (such as Tahiti), and atolls or nearatolls (such as Maupihaa and Maupiti). The reefs’ biological diversity is moderate compared with the reefs of Southeast Asia, although more than 160 coral species, 800 species of reef fish, 1,000 species of mollusc, and 30 species of echinoderm have been

ANIMAL LIFE

Patella vulgata

B

e

North-central Pacific

The Hawaiian Archipelago consists of the exposed peaks of a huge undersea mountain range. These mountains have formed over tens of millions of years as the Pacific Plate moves

PACIFIC OCEAN L4

Cascadia Basin

600,000 sq. miles (1.5 million sq. km)

CONDITION

French Polynesia, northeast of New Zealand, south-central Pacific

R is

LOCATION

AREA

MAXIMUM DEPTH

LOCATION

ev

Coral disease outbreaks reported

CONDITION

Good, but significant local damage

where the contact is between ocean crust and continental crust. The largest volcanic event of the 20th century was the eruption of Mount Katmai on the Alaskan Peninsula in 1912. This boundary can also produce powerful earthquakes such as the event that destroyed part of Anchorage in 1964.

ch

1,180 square km (450 square miles)

AREA

1,500 square km (600 square miles)

AREA

SEALS IN THE ALEUTIAN ISLANDS

ru

Fringing reefs, atolls, submerged reefs

TYPE

3 in (8 cm) per year

Ob

Hawaiian Archipelago

northwest over a hotspot in the Earth’s mantle. Coral reefs fringe some coastal areas of the younger, substantial islands at the southeastern end of the chain, such as Oahu and Molokai. To the northwest, located on the submerged summits of older, sunken islands, are several near-atolls (such as the French Frigate Shoals) and atolls (such as Midway Atoll). These reefs are highly isolated from all other coral reefs in the world, and although their overall biological diversity is relatively low, many new species have evolved on them. The more remote reefs are healthy, but in 2013, a serious coral disease was reported affecting reefs on Oahu and Kauai.

26,600 ft (8,100 m)

The Bering Sea is bounded to the south by the Aleutian Islands. On the Pacific side of the islands lies the Aleutian Trench, marking where the Pacific Plate is plunging beneath the North American Plate. It is this subduction zone that gives rise to the volcanic arc of islands, the most northerly link in the Pacific Ring of Fire. The trench continues to the east,

OCEAN ENVIRONMENTS

PACIFIC OCEAN CENTRAL

2,000 miles (3,200 km)

RATE OF CLOSURE

Amuk ta P a ss

As with many Pacific atolls, the rim of Majuro Atoll consists partly of shallow submerged reef and partly of small, low-lying islands.

LENGTH

Pacific Ocean; Yukon, Anadyr’ rivers

The Bering Sea is named after a Danish navigator in the Russian Navy, who explored the area in 1741. It lies between mainland Asia and North America, and is bounded by the Aleutian Islands to the south and linked to the Arctic Ocean in the north by the narrow Bering Strait. There is a flow of cold Arctic water south through this strait, feeding a counterclockwise circulation. The main freshwater input is the Yukon River, which has deposited an extensive delta at its mouth. The Bering Sea is one of the world’s richest fisheries, helping Alaska account

PACIFIC OCEAN I3

Gulf of Alaska

e

MAJURO ATOLL

Aleutian Trench

20,021 ft (6,102 m)

aP ass

Generally good; some episodes of coral bleaching

CONDITION

Fringing reefs, barrier reefs, atolls

TYPE

INFLOWS

PACIFIC OCEAN

MAXIMUM DEPTH

890,000 square miles (2.3 million square km)

Am chi tk

6,200 square km (2,400 square miles)

AREA

Micronesia, southwest of Hawaii, western Pacific

LOCATION

Society Islands

AREA

MAXIMUM DEPTH

THE COLD, STORMY SUBPOLAR SEAS of the North Pacific are highly productive, supporting a rich fishery. Geologically, the area is dominated by a subduction zone, and the area’s volcanoes and earthquakes pose an ever-present danger.

recorded. The reefs’ health is generally good, but some reefs around the busy holiday destination islands of Tahiti, Moorea, and Bora-Bora have been severely affected by construction, sewage, and sediment run-off.

for about half of the total US fish and shellfish catch. Harbor seals and gray whales also take advantage of these productive waters. In contrast to the deep ocean basin beneath the southwestern half of the sea, the broad continental shelf in the northwest is very shallow. Much of this area formed a land bridge during the last ice age, when sea levels were up to 390 ft (120 m) lower than they are today. This route was ice-free for extended periods, allowing several species, including humans, to migrate from Asia to North America on foot for the first time.

PACIFIC OCEAN D3

Bering Sea

An a

Humphead Parrotfish, and various species of octopuses and nudibranchs (sea slugs). Major threats to the reefs in Nusa Tenggara include pollution from land-based sources, removal of fish for the aquarium trade, and reef destruction by blast fishing. Coral bleaching affected some reefs in 2010.

Atolls

PACIFIC OCEAN SOUTHWEST

459

The Bering Sea And Gulf of Alaska

ge

TYPE

The Marshall Islands consist of 29 coral atolls and five small islands in the western Pacific. The atolls lie on top of ancient volcanic peaks that are thought to have erupted from the ocean floor 50-60 million years ago. They include Kwajalein, the largest atoll in the Pacific at 2,500 square km (1,000 square miles), and Bikini and Enewetak atolls, which were used by the USA for testing nuclear weapons between 1946 and 1962. Human pressures on these two remote, evacuated atolls have been minimal during the past 50 years, and marine life around them now thrives; for example, 250 species of coral and up to 1,000 species of fish have been recorded at Bikini.

THE PACIFIC OCEAN

458

One of the tiniest residents of the Great Barrier Reef, at just 7–8mm (less than 1⁄3in) long from snout to tail, is the Stout Infantfish. When discovered in 2004, the Infantfish was declared to be the world’s smallest vertebrate species. That title has since been claimed first by a slightly smaller species of Indonesian cyprinid fish, and more recently by a tiny species of frog, about 7mm (1⁄4in) long, found in Papua New Guinea.

Rid

Marshall Islands

However, a study published in 2012 reported that the reef has lost more than half its coral cover since 1985. The factors causing this damage include pollution, tropical cyclones, raised water temperature causing mass coral bleaching, population outbreaks of the Crown-of-thorns Starfish, overfishing, and shipping accidents.

THE WORLD’S SMALLEST VERTEBRATE?

ov

PACIFIC OCEAN SOUTHWEST

In this view of a central area of the reef, a deep, meandering channel separates two reef platforms. The region’s high tidal range drives strong currents through such channels.

sh

lving coral f

REEF CHANNEL

ir

Australia’s Great Barrier Reef, which stretches 2,010km (1,250 miles), is the world’s largest coral reef system. Often described as the largest structure ever made by living organisms, it in fact consists of some 3,000 individual reefs and small coral islands. Its outer edge ranges from 30 to 250km (18 to 155 miles) from the mainland, and its biological diversity is high. The reef contains about 350 species of stony coral and many of soft coral. Its 1,500 species of fish range from 45 species of butterflyfish, to several shark species, including silvertip, hammerhead, and whale sharks. The reef is also home to 500 species of algae, 20 species of sea snake, and 4,000 species of mollusc.

284

all maps are accompanied by a written description of location

Damaged by tropical storms, pollution, and an unbalanced ecosystem

CONDITION

bbataha vers in the 1980s mage tices and ed farm.

diversity of r example, n more more than mbined), reefimals here Rays,

Barrier reef

37,000 square km (14,300 square miles)

AREA

Sh

TYPE

Em pe r or Se a mou nts

he Philippines

und two u Sea and e pelagic attracted nta Rays, eeply ch in pecies ibranchs 0 species

Great Barrier Reef

m

Good; from coral n 2010

161

PACIFIC OCEAN SOUTHWEST

Ka

s

square km e miles)

In 1988, the Philippines government intervened, declaring the area a National Marine Park, and since 1993 it has also been a UNESCO World Heritage Site. The condition of the Tubbataha reefs has much improved, due to the enforcement of measures such as a prohibition on fishing and a ban on boats anchoring on the reefs (visiting craft must use mooring buoys). A setback occurred in January 2013 when a US Navy minesweeper ran aground on the reef, damaging over 2,000 square m (21,500 square ft).

The final chapter of the book is an atlas of the world’s oceans. It includes maps of the five major oceans. The pages that immediately follow each whole-ocean map contain more detailed maps of selected regions of that ocean. All the maps have been produced using data collected from a combination of satellite- and ship-borne instruments. They are labeled to show the names of the seas, undersea features (such as ridges, trenches, and seamounts), and prominent coastal features. They also show ocean depths and ▼ REGIONAL MAP the boundaries between tectonic As well as maps, these pages also include plates. Features identified on the profiles of individual seas or undersea maps have been included in the features. The example shown here is from the section on the Pacific Ocean. index at the end of the book.

AT L A S O F T H E O C E A N S

name of ocean in which feature is found

compass direction indicates position within ocean

FOREWORD

W

e should call our planet Ocean. A small orb floating in the endless darkness of space, it is a beacon of life in the otherwise forbidding cold of the endless universe. Against all odds, it is also the Petri dish from which all life known to us springs. Without water, our planet would be just one of billions of lifeless rocks floating endlessly in the vastness of the inky-black void. Even statisticians revel in the improbability that it exists at all, with such a rich abundance of life, much less that we as a species survive on its surface. Yet, despite the maze of improbability, we have somehow found our way to where we are today. Humans were enchanted by the sea even before the Greek poet Homer wrote his epic tale of ocean adventure, the Odyssey. It is this fascination that has driven us to delve into this foreign realm in search of answers, but the sea has always been reluctant to give up its secrets easily. Even with the monumental achievements of past explorers, scientists, and oceanographers, we have barely ventured through its surface. It is estimated that over 90 percent of the world’s biodiversity resides in its oceans. From the heartbeat-like pulsing of the jellyfish to the life-and-death battle between an octopus and a mantis shrimp, discoveries await us at every turn. And for every mystery solved, a dozen more present themselves. These are certainly exciting times as we dive into the planet’s final frontier. Aided by new technology, we can now explore beyond the two percent or so of the oceans that previous generations observed. But even with the advent of modern technology, it will take several more generations to achieve a knowledge base similar to the one we have about the land. No matter how remote we feel we are from the oceans, every act each one of us takes in our everyday lives affects our planet’s water cycle and in return affects us. All the water that falls on land, from the highest peaks to the flattest plains, ends up draining into the oceans. And although this has happened for countless millions of years, the growing ecological footprint of our species in the last century has affected the cycle in profound ways. From fertilizer overuse in landlocked areas, which creates life-choking algal blooms thousand of miles away, to everyday plastic items washing up in even the most remote areas of the globe, our actions affect the health of this, our sole life-support system. This statement is not here to make us feel that we are doomed by our actions, but rather to illustrate that through improved knowledge of the ocean system and its inhabitants, we can become impassioned to work toward curing our planet’s faltering health. By taking simple steps, such as paying a little more attention to our daily routines, each one of us can have a significant positive impact on the future of our planet and on the world our children will inherit. In short, it would be much healthier for us to learn to dance nature’s waltz than to try to change the music.

MOVING EN MASSE

The fast, coordinated movement of a shoal of fish is one of the most spectacular sights in the oceans. These blackfin barracuda have formed a spiraling shoal in water around the Solomon Islands. Such shoals are often found in the same place several months, or even years, apart.

Fabien Cousteau

GOLDEN JELLYFISH

Drawn to the light, Jellyfish in the genus Mastigias follow the sunlight around their brackish lake home in Palau. Stained golden-brown by algae in their tissues, they carry their photosynthetic passengers to the best-lit areas. In return, the algae provide them synthesized food. Isolated from the sea, these jellyfish are found nowhere else in the world.

NORTHERN EXPOSURE

The world’s shorelines can be inhospitable places to live. Common murres nest in colonies, favoring rocky cliffs. These birds are clinging to a rock off the Scottish coast, while being battered by a fierce gale. During the storm, many of the birds were swept off the rock and some of their eggs were washed into the sea. PROTECTION OF THE YOUNG

The packhorse lobster inhabits the continental shelves off Australia and New Zealand. The female shown here is carrying eggs under her abdomen. Up to two million eggs at a time can be stored in this way. Despite producing eggs in such prodigious numbers, these lobsters are threatened by overfishing and catches are now restricted.

FILTER-FEEDING WITH FEATHERS

Instead of moving around in search of food, many marine animals spend their lives fixed to the sea bed, collecting food as it drifts past. These feather-like funnels are actually part of the body of a worm. The worm beats tiny, hair-like structures to set up a current through the funnels and then traps food from the moving water.

NEW COASTLINE

The shape of a coastline is determined by a balance of forces. The coastlines of the Galápagos Islands in the eastern Pacific are relatively new, having formed when the islands were created by volcanic eruptions. The lava seen here solidified about 100 years ago, but more recent eruptions have occurred on some of the group’s younger islands. THE FALL OF THE APOSTLES

On this part of the southern Australian coast, marine erosion is the dominant force. A line of limestone cliffs is slowly being worn back by the sea, leaving behind isolated stacks of rock. The stacks are collectively known as the Twelve Apostles, although when they were named there were only nine of them and there are now just eight.

LIVING ON THE BOTTOM

The flattened body of a ray is an adaptation for life on the bottom of the sea. Most rays feed on animals on the seabed, and so their mouths are on the undersides of their bodies. They have flat teeth, which they use to grasp and then grind food. The features that resemble eyes are actually the ray’s nostrils.

AVOIDING A STING

Clownfish have a remarkable relationship with some anemones, feeding and sleeping among them. The anemones’ stinging tentacles repel all other fish, but the clownfish avoid triggering the firing of the anemones’ stinging cells with an undulating swimming action and by secreting chemicals that suppress the firing process. LEARNING TO SWIM

Being able to swim is a useful skill for polar bears, which for part of the year track their prey across shifting sea ice in the Arctic Ocean and are sometimes seen in the water many miles from land. While underwater, they keep their eyes open but close their nostrils. They can remain submerged for up to two minutes.

NUDIBRANCH

Crawling over a vivid red seafan in the Komodo National park, Indonesia, this brightly colored nudibranch, or sea slug, stands out. Its scientific name, Phyllidia pustulosa, reflects the diseaselike nodules on its back. These yellow beacons warn fish that it contains toxins and they should not eat it.

THE GREENLAND COAST

In this satellite image of part of Greenland’s eastern coast, taken during a summer thaw, the brown areas are rocky land. Penetrating it are many long fiords, some partly filled by glaciers and large, flat icebergs. Other icebergs of varying size, formed from a disintegrated ice shelf, float offshore in vast numbers.

INTRODUCTION

EARTH’S OCEANS CONTAIN about

320 million cubic miles (1.34 billion cubic kilometers) of seawater. Dissolved in this are some 53 million billion tons (48 million billion metric tons) of salts, gases, and other substances. The base substance, water itself, has many unusual properties, such as its high surface tension and heat capacity, which are of tremendous significance to everything from the oceans’ ability to support life to their stabilizing effect on the world’s climate, and their ability to transmit waves. Also of significance is the variability of ocean water—the sea is not uniform but varies spatially and sometimes seasonally in attributes such as its temperature, pressure, dissolved-oxygen content, and level and quality of light illumination. These attributes are important in numerous key respects.

OC E A N WAT E R CRASHING WAVE

This “barrel” wave is crashing onto the north shore of the island of Oahu, Hawaii. Inspiring sights such as this are only possible because of some of the unusual properties of water.

30

OCEAN WATER hydrogen atom consists of one proton and one electron

The Properties of Water

hydrogen nucleus, consisting of single proton, contains positive charge

THE MAIN CONSTITUENT OF THE OCEANS IS, of

course, water. The presence of large amounts of liquid water on Earth’s surface over much of its history has resulted from a fortunate combination of factors. Among them are water’s unusually high freezing and boiling points for a molecule of its size, and its relative chemical stability. Water also has other remarkable properties that contribute to the characteristics of oceans—from their + + ability to support life to effects on climate. Underlying these properties is water’s molecular structure. water molecule

– region of slight negative charge

hydrogen bond

The Water Molecule

hydrogen bond

+

+ –

– +

+ region of slight positive charge

–

+

shared electron

one of eight electrons in oxygen atom oxygen

atom free A molecule of water (H2O) consists of two hydrogen (H) electron atoms bound to one atom of oxygen (O). Crucial to formation of the bonds between the oxygen and hydrogen atoms are four tiny negatively charged particles called electrons, which are shared between the atoms. In addition, six other electrons move around HYDROGEN BONDS within different regions of the oxygen atom. This A hydrogen bond is an electron arrangement makes the H2O molecule attractive electrostatic chemically stable but gives it an unusual shape. It also force between regions of produces a small imbalance in the distribution of slight positive and negative charge on neighboring water electrical charge within the molecule. An important molecules. Several bonds result of this is that neighboring water molecules are are visible here. drawn to each other by forces called hydrogen bonds.

oxygen nucleus, containing protons and neutrons, has positive charge

CHARGE IMBALANCE

The distribution of negative charges (electrons) and regions of positive charge in an H2O molecule causes one side to carry a slight positive charge and the other side a slight negative charge.

water molecule at surface

WALKING ON WATER

INTRODUCTION

Certain insects, such as sea skaters and water striders (pictured below), exploit surface tension to walk, feed, and mate on the surface of the sea, lakes, or ponds.

Surface Tension

hydrogen bonds

One special property of liquid water that can be directly attributed to the attractive forces between its molecules is its high surface tension. In any aggregation of water molecules, the surface molecules tend to be drawn together and inward toward the center of the aggregation, water forming a surface “skin” that is resistant to disruption. Surface molecule tension can be thought of as the force that has to be exerted below surface or countered to break through this skin. Water’s high surface tension has various important effects. Perhaps the most crucial is that it is vital to certain processes within living organisms—for example, water transport in plants and blood transport in animals. Surface tension also allows small insects such as sea skaters to walk and feed on the ocean surface, and it even plays a part in the formation of ocean waves (see p.76).

CAUSE OF SURFACE TENSION

In a drop of water, molecules are pulled in all directions by hydrogen bonding with their neighbors. But at the surface, the only forces act inward, or sideways, toward other surface molecules.

WATER DROPLETS

The shape of these droplets results from surface tension. The forces pulling their surface molecules together are stronger than the gravitational forces flattening them.

THE PROPERTIES OF WATER LAND AND SEA

31

Heat Capacity

Water’s high heat capacity means that the Sun warms the sea more slowly than land. In this satellite-generated temperature map of south California during a heat wave, much of the land (red) is 122ºF (50ºC) or more, but the sea (left) is cool, at 50ºF (10ºC).

A second property of liquid water that can be attributed to hydrogen bonding is its unusually high heat capacity, which exceeds that of nearly all other known liquids (see table, left). When heat is added to water, most of the heat is used to break hydrogen bonds linking the molecules. Only a fraction of the energy increases the vibrations of the water molecules, which are detected as a rise in temperature. This means that areas of ocean can absorb and release huge amounts of heat energy with little change in temperature. It also means that movements of water— ocean currents—transfer enormous amounts of heat energy around the planet. This role of ocean currents is vital to Earth’s climate (see p.66).

SPECIFIC HEAT CAPACITY Specific heat capacity (SHC) is the energy (in joules) needed to raise the temperature of 1 gram of a substance by 1ºC. Listed below are the SHCs of 13 liquids, measured at room temperature unless otherwise stated. SUBSTANCE

JOULES/GRAM ºC

Liquid ammonia at –40ºF (–40ºC)

4.7

Fresh water

4.19

HEAT ON THE MOVE

Seawater at 35ºF (2ºC)

3.93

In this temperature map of part of the northwest Atlantic, the water surface ranges from about 41ºF (5oC) (blue) to 77ºF (25ºC) (red). A warm current, the Gulf Stream is visible in red.

Glycerin

2.43

Ethanol (ethyl alcohol)

2.4

Acetone

2.15

Kerosene

2.01

Olive oil

1.97

Benzene

1.8

Turpentine

1.72

Freon 12 refrigerant at -40ºF (-40ºC)

0.88

Bromine

0.47

Mercury

0.14

WATER TWISTER

The effects of surface tension can cause moving sheets, jets, and streams of water to assume or hold together in some surprising forms, as in this slightly spiral-shaped water jet.

Three States of Water The temperatures at which water changes between its three states— melting point (ice to liquid water) and boiling point (liquid water to water vapor)—are both high compared with substances having similarly sized molecules. For ice to melt and water to vaporize, high levels of energy are needed to break all the hydrogen bonds. Water is also unusual in that its solid form is slightly less dense than its liquid form, so ice floats in liquid water. The reason for this is that the molecules in ice are loosely packed, whereas those in liquid water move around in snugly packed groups. The fact that ice floats on liquid water is important because it allows the existence of large areas of polar sea ice (see pp. 198–199). These affect heat flow between ocean and atmosphere and help stabilize ocean temperatures and Earth’s climate.

SOLID, LIQUID, AND GAS ICE

LIQUID WATER

WATER VAPOR

Hexagonal crystal lattice

Small clumps of bonded molecules

Widely spaced unbonded molecules

In ice, hydrogen bonds hold the water molecules together in a rigid structure. In liquid water, the bonds hold the molecules in small, moving clumps. In water vapor, there are no hydrogen bonds.

Water is the only natural substance found in all three states at Earth’s surface. Sometimes, ice, liquid water, and condensing water vapor can be seen side by side, as here at the fjord in Spitsbergen.

INTRODUCTION

SIDE BY SIDE

32

OCEAN WATER

The Chemistry of Seawater

volcanic ash drifts down to sea

THE OCEANS CONTAIN MILLIONS OF DISSOLVED

chemical substances. Most of these are present in exceedingly small concentrations. Those present in significant concentrations include sea salt, which is not a single substance but a mixture of charged particles called ions. Other constituents include gases such as oxygen and carbon dioxide. One reason the oceans contain so many dissolved substances is that water is an excellent solvent.

The Salty Sea

salts are leached from rocks into rivers and streams and flow to ocean

The salt in the oceans exists in the form of charged particles, called ions, some positively charged and some negatively charged. The most common of these are sodium and chloride ions, the components of ordinary table salt (sodium chloride). Together they make up about 85 percent by mass of all the salt in the sea. Nearly all the rest is made up of the next four most common ions, which are sulfate, magnesium, calcium, and potassium. All these ions, together with several others present in smaller quantities, exist throughout the oceans in fixed proportions. Each is distributed extremely uniformly—this is in contrast to some other dissolved substances in seawater, which are unevenly distributed.

salt spray onto land

nutrients from soil wash into rivers and streams, and flow to ocean

BREAKDOWN OF SALT

If 2½ gallons (10 liters) of seawater are evaporated, about 123/4 oz (354 g) of salts are obtained, of the types shown below. 2½ gallons (10 liters) of seawater

other salts 1/4oz (7.5g) calcium sulfate (gypsum) 2/3oz (17.7g) magnesium salts 2oz (54.8g) sodium chloride (halite) 10oz (274g)

+ +

+ – –

+

– Na+

–

–

– –

+

WATER AS A SOLVENT

+

slow uplift of sedimentary rocks at continental margins, exposing salts, minerals, and ions at surface

–

sodium chloride crystal

+ –

+

+ Cl–

+

water molecule

+

ALEXANDER MARCET The Swiss chemist and doctor Alexander Marcet (1770–1822) carried out some of the earliest research in marine chemistry. He is best known for his discovery, in 1819, that all the main chemical ions in seawater (such as sodium, chloride, and magnesium ions) are present in exactly the same proportions throughout the world’s oceans. The unchanging ratio between the ions holds true regardless of any variations in the salinity of water and is known today as the principle of constant proportions.

+ –

+ + –

–

PEOPLE

uptake of nutrients by phytoplankton

–

–

chloride ion (negative charge)

INTRODUCTION

+

–

+

The charge imbalance on its molecules makes water a good solvent. When dissolving and holding sodium chloride in solution, the positive ends of the molecules face the chloride ions and the negative ends face the sodium ions.

sodium ion (positive charge)

–

Sources and Sinks

nutrient upwelling exchange of gases between phytoplankton and seawater

sinking and

decomposition The ions that make up the salt in the oceans have arrived of dead there through various processes. Some were dissolved out of organisms rocks on land by the action of rainwater and carried to the sea in rivers. Others entered the sea in the emanations of hydrothermal vents (see p.188), in dust blown off the land, or came from volcanic ash. There are also “sinks” for every type of ion—processes that remove them from seawater. These range from salt spray onto land to the precipitation of various ions onto the seafloor as mineral deposits. Each type of ion has a characteristic residence time. This is the time that an ion remains in seawater before it is removed. The common ions in seawater have long residence times, ranging from a few hundred years to hundreds of millions of years.

RIVER DISCHARGE

River discharge is a mechanism by which ions of sea salt and nutrients enter the oceans. Here, the Noosa River empties into the sea on the coast of Queensland, Australia.

THE CHEMISTRY OF SEAWATER SOURCES, SINKS, AND EXCHANGES

spread of volcanic ash and gases into rain clouds

Shown here are various sources, sinks, and exchange processes for the ions, salts, and minerals (yellow arrows), gases (pink arrows), and plant nutrients (turquoise arrows) in seawater.

KEY

33

Gases in Seawater

gases ions, salts, and minerals plant nutrients

The main gases dissolved in seawater are nitrogen (N), oxygen (O2), and carbon dioxide (CO2). The levels of O2 and CO2 vary in response to the activities of photosynthesizing organisms (phytoplankton) and animals. The level of O2 is generally highest near the surface, where the gas is absorbed from the air and also produced by photosynthesizers. Its concentration drops to a minimum in a zone between about 660 ft (200 m) and 3,300 ft (1,000 m), where oxygen is consumed by bacterial oxidation of dead organic matter and by animals feeding on this matter. Deeper down, the O2 level increases again. CO2 levels are highest at depth and lowest at the surface, where the gas is taken up by photosynthesizers faster than it is produced by respiration. CARBON SINK

washing of ions from volcanic dust and gases into sea, dissolved in rain

Many marine animals, such as nautiluses (below), use carbonate (a compound of carbon and oxygen) in seawater to make their shells. After they die, the shells may form sediments and eventually rocks.

dust blown off land

exchange of gases between animals and seawater

exchange of gases between ocean and atmosphere

OXYGEN PRODUCER AND CONSUMER

Oxygen levels in the upper ocean depend on the balance between its production by photo-synthesizing organisms, such as kelp, and its consumption by animals, such as fish.

Nutrients

release of minerals from hydrothermal vents dissolving of minerals from sea floor precipitation of minerals onto sea floor

PLANKTON BLOOM

This satellite image of the Skagerrak (a strait linking the North and Baltic seas) shows a bloom of phytoplankton, visible as a turquoise discoloration in the water.

SILICEOUS DIATOMS

These tiny forms of planktonic organisms have cell walls made of silicate. They can only grow if there are sufficient amounts of silica present in the water.

INTRODUCTION

carbonates incorporated into seafloor sediments from animal shells

Numerous substances present in small amounts in seawater are essential for marine organisms to grow. At the base of the oceanic food chain are phytoplankton—microscopic floating life-forms that obtain energy by photosynthesis. Phytoplankton need substances such as nitrates, iron, and phosphates in order to grow and multiply. If the supply of these nutrients dries up, their growth stops; conversely, blooms (rapid growth phases) occur if it increases. Although the sea receives some input of nutrients from sources such as rivers, the main supply comes from a continuous cycle within the ocean. As organisms die, they sink to the ocean floor, where their tissues decompose and release nutrients. Upwelling of seawater from the ocean floor (see p.60) recharges the surface waters with vital substances, where they are taken up by the phytoplankton, refueling the chain.

34

OCEAN WATER

Temperature and Salinity OCEAN WATER IS NOT UNIFORM BUT VARIES

in several physical attributes, including temperature, salinity, pressure, and density. These vary vertically (dividing the oceans into layers), horizontally (between tropical and temperate regions, for example), and seasonally. The basic variables, temperature and salinity, in turn produce variations in density that help drive deep-water ocean circulation.

Temperature Temperature varies considerably over the upper areas of the oceans. In the tropics and subtropics, solar heating keeps the ocean surface warm throughout the year. Below the surface, the temperature declines steeply to about 8–10˚C (46-50˚F) at a depth of 1,000m (3,300ft). This region of steep decline is called a thermocline. Deeper still, temperature decreases more gradually to a uniform, near-freezing value of about 2˚C (36˚F) on the sea floor – this temperature subsists throughout the deep oceans. In mid-latitudes there is a much more marked seasonal variation in surface temperature. In high latitudes and polar oceans, the water is constantly cold, sometimes below 0˚C (32˚F).

LA NIÑA TEMPERATURE ANOMALY IN PACIFIC

The Pacific experiences long-term fluctuations in the temperature patterns of its surface waters, which are linked to climatic disturbances known as El Niño and La Niña. This visualization, based on satellite data, shows a strong La Niña-type surface temperature pattern that developed in late 2010, with a blue band indicating lower than normal temperatures in the eastern Pacific.

cool surface waters caused by cold current moving up coast

OCEAN SURFACE TEMPERATURE

This map shows average surface temperatures in March. Proximity to the equator is the main factor determining surface temperature, but ocean currents also play a role.

warm tropical water, with temperatures constantly above 25˚C (77˚F) region of variable surface temperature, fluctuating seasonally from 7 to 20˚C (45–68˚F)

constantly cold water with temperatures in the range 0–3˚C (32–37˚F)

North America

constantly cold water off Greenland

constantly warm pool of water in Caribbean Sea

INTRODUCTION

warm surface waters caused by warm current moving down southeast coast

thermocline, where temperature declines rapidly with depth

South America

TEMPERATURE AND DEPTH

cold bottom water at a uniform temperature of 2˚C (36˚F)

Shown in early summer, the vast bulk of ocean water in this part of the north Atlantic is uniformly cold (below 5˚C/41˚F). Only a thin surface layer from the tropics into mid- latitudes is warmed above this base level.

KEY

90°F

32°C 30°C

70°F

20°C

50°F

10°C

30°F

0°C

35

Salinity

Pressure

Salinity is an expression of the amount of salt in a fixed mass of seawater. It is determined by measuring a seawater sample’s electrical conductivity and averages about 35 grams of salt per kilogram of seawater. Salinity varies considerably over the surface of oceans – its value at any particular spot depends on what processes or factors are operating at that location that either add or remove water. Factors that add water, causing low salinity, include high rainfall, river input, or melting of sea-ice. Processes that remove water, causing high salinity, include high evaporative losses and sea-ice formation. At depth, salinity is near constant throughout the oceans. Between the surface and deep water is a region called a halocline, where salinity gradually increases or decreases with depth. Salinity affects the freezing point of seawater – the higher the salinity, the lower the freezing point.

Scientists measure pressure in units called bars. At sea level, the weight of the atmosphere exerts a pressure of about one bar. Underwater, pressure increases at the rate of one bar for every 10m (33ft) increase in depth, due to the weight of the overlying water. This means that at 70m (230ft), for example, the total pressure is eight bars or eight times the surface pressure. This pressure increase poses a challenge to human exploration of the oceans. To inflate their lungs underwater, divers have to breathe pressurized air or other gas mixtures, but doing DECOMPRESSION STOP so can cause additional To avoid a condition called “bends” that can arise from problems (arising from the dissolution of excess decompressing too quickly, on their way to the surface gas in body tissues). scuba divers make one or These problems limit more timed stops to release excess gas. the depths attainable.

NATURAL ADAPTATION

Elephant seals can dive to depths of up to 1,550m (5,100ft). They have evolved various adaptations for coping with the high pressure, including collapsible ribcages.

KEY

EASY FLOATING

GLOBAL SALINITY

In some enclosed seas where evaporative losses are high and there is little rainfall or river inflow, the sea- water can become so saline and dense that floating becomes easy. This is the case here in the Dead Sea.

Surface salinity is highest in the subtropics, where evaporative losses of water are high, or in enclosed or semi-enclosed basins (such as the Mediterranean). It is lowest in colder regions or where there are large inflows of river water.

37 36 35 34 33 32 31 30 29 under 29 parts per thousand (‰)

Density

DECOMPRESSION After working underwater for hours at a time, professional divers routinely undergo controlled decompression in a purpose-built pressure chamber. These facilities are also used to treat pressure-related diving illnesses and for research into diving physiology. PRESSURE CHAMBER

The person being decompressed may have to breathe a special gas mixture while the ambient pressure is slowly reduced.

warm surface flow

Atlantic Central Water: warm, low-density surface waters in the tropics and subtropics

Atlantic Intermediate Water: cool layer of intermediate density, forms and sinks in north Atlantic, then moves south

DENSITY LAYERS IN ATLANTIC

The oceans each contain distinct, named water masses that increase in density from the surface downwards. The denser, cooler masses sink and move slowly towards the Equator. The cold, high-density deep and bottom waters comprise 80 per cent of the total volume of the ocean.

Antarctic Bottom Water: coldest and densest layer, forms close to Antarctica, sinks then moves north

mid-ocean ridge

North Atlantic Deep Water: cold, dense water, forms and sinks in north Atlantic, then moves south

INTRODUCTION

The density of any small portion of seawater depends primarily on its temperature and salinity. Any decrease in temperature or increase in salinity makes seawater denser – an exception being a temperature drop below 4˚C (39˚F), which actually makes it a little less dense. In any part of the ocean, the density of the water increases with depth, because dense water always sinks if there is less dense water below it. Processes that change the density of seawater cause it to either rise or sink, and drive large-scale circulation in the oceans between the surface and deep water (see p.60). Most important is water carried towards Antarctica and the Arctic Ocean Antarctic Intermediate fringes. This becomes denser as it Water: cool layer intermediate cools and through an increase in of density, sinks and its salinity as a result of sea-ice moves north formation. In these regions large quantities of cold, dense, salty water continually form and sink towards the ocean floor.

DISCOVERY

36

OCEAN WATER

Light and Sound LIGHT AND SOUND BEHAVE VERY DIFFERENTLY

DEPTH

Violet

Blue

Green

570nm 400nm

510nm

60m

Yellow

(100ft)

Light in the Ocean 590nm

650nm

30m

Orange

Red

in water than in air. Most light wavelengths are quickly absorbed by water, a fact that both explains why a calm sea appears blue and why ocean life is concentrated near its surface – almost the entire marine food chain relies on light energy driving plant growth. Sound, in contrast, travels better in water, a fact exploited by animals such as dolphins.

(200ft)

475nm

90m (300ft)

LIGHT PENETRATION

The red and orange components of sunlight are absorbed in the top 15m (50ft) of the ocean. Most other colours are absorbed in the next 40m (130ft). Wavelength is measured in nanometres (nm).

White light, such as sunlight, contains a mixture of light wavelengths, ranging from long (red) to short (violet). Ocean water strongly absorbs red, orange, and yellow light, so only some blue and a little green and violet light reach beyond a depth of about 40m (130ft). At 90m (300ft), most of even the blue light (the most penetrating) has been absorbed, while below 200m (650ft), the only light comes from bioluminescent organisms, which produce their own light (see p.224). Because they rely on light to photosynthesize, phytoplankton are restricted to the upper layers of the ocean, and this in turn affects the distribution of other marine organisms. Intriguingly, many bright red animals live at depths that are devoid of red light: their colour provides effective camouflage, since they appear black.

COLOUR RESTORATION

At a depth of 20m (65ft), most animals and plants look blue-green under ambient light conditions (top). Lighting up the scene with a photographic flash or torch reveals the true colours of the marine life (bottom).

INTRODUCTION

FISH VISION

FIREFLY SQUID

This squid produces a pattern of glowing spots (photophores). When viewed by a predator swimming below, the spots help camouflage its outline against the moonlit waters above.

Fish have excellent vision, which helps them f ind food and avoid predators. Many can see in colour. The lens of a fish’s eye is almost spherical and made of a material with a high refractive index. It can be moved backwards and forwards to focus light on the retina. FISH EYE

The lens of a fish’s eye bulges through the iris (the dark central part) almost touching the cornea (outer part). This helps to gather the maximum amount of light and gives a wide field of view.

LIGHT AND SOUND

Seen from underwater, only a part of the surface of the sea appears lit up, while the rest looks dark. This is an effect of the way light waves are bent (refracted) when they enter the sea from the air.

Sea Colours Seawater has no intrinsic colour – a glass of seawater is transparent. But on a clear, sunny day, the sea usually looks blue or turquoise. In part, this is due to the sea surface reflecting the sky, but the main reason is that most of the light coming off the surface has already penetrated it and been reflected back by particles in the water or by the sea bed. During its journey through the water, most of the light is absorbed, except for some blue and green light, which are the colours seen. Other factors can modify the sea’s colour. In windy weather, the surface becomes flecked with white, caused by trapped bubbles of air, which reflect most of the light that hits them. Rain interferes with seawater’s light-transmitting properties, so rainy, overcast weather generally produces dark, grey-green seas. Occasionally, living organisms, such as “blooms” of plankton can turn patches of the sea vivid colours.

VIVID GREEN FROM ALGAL BLOOM

TROPICAL TURQUOISE

OCEAN SHADES

A green sea (top) is sometimes caused by the presence of algae. Turquoise is the usual shade in clear tropical waters, while grey water flecked with white foam is typical of windy, overcast days.

GREY FOAMY TEMPERATE SEA

Underwater Sounds

PEOPLE

WALTER MUNK The Austrian-American scientist Walter Munk (b.1917) pioneered the use of sound waves in oceanography. A professor at the Scripps Institute of Oceanography in San Diego, California, Munk demonstrated that by studying the patterns and speed of sound propagation underwater, information can be obtained about the large-scale structure of ocean basins.

The oceans are noisier than might be imagined. Sources of sound include ships, submarines, earthquakes, underwater landslides, and the sounds of icebergs breaking off glaciers and ice shelves. In addition, by transmitting sound waves or bouncing them off underwater objects (echolocation) whales and dolphins use sound for navigation, hunting, and communication. Sound waves travel faster and further underwater than they do in air. Their speed underwater is about 1,500m (5,000ft) per second and is increased by a rise in the pressure (depth) of the water and decreased by a drop in temperature. Combining these two effects, in most ocean regions, there is a layer of minimum sound velocity at a depth of about 1,000m (3,300ft). This layer is called the SOFAR (Sound Fixing and Ranging) channel. The properties of the SOFAR channel are exploited by people using underwater listening devices and, it has been theorized, by animals such as whales and dolphins. HUMPBACK WHALE SONG

The peaks and troughs in this spectrogram show the changes in frequency of a few seconds of repeated sound made by a Humpback Whale. THE SOFAR CHANNEL

sound travels slower within channel

1,000m

SOFAR channel

(3,300ft) 2,000m (6,600ft) 3,000m (9,800ft) 1,500m/s 1,525m/s 1,550m/s (4,900ft/s) (5,000ft/s) (5,085ft/s)

SPEED OF SOUND UNDERWATER

Low-frequency sounds generated in the SOFAR channel are “trapped” in it by inward refraction from the edges of the channel. As a result, sounds can travel very long distances in this ocean layer.

INTRODUCTION

Sea level

DEPTH

LOOKING UP

37

OCEANS ARE ALMOST as old as

Earth itself. Sediments were probably accumulating underwater about 4 billion years ago, around the time that the oldest known rocks on Earth were forming. And yet the ocean floor is very young. Discovery of the processes that create and rapidly recycle the ocean floor led to our modern understanding of plate tectonics. These processes give Earth a surface quite unlike those of our planetary neighbors, with deep ocean basins and high-standing continents. The positions of the oceans and continents are not fixed, but driven by heat flow deep within the planet. An understanding of ocean geology opens a window on Earth’s interior, as well as providing insights into the global climate and the evolution of life on Earth.

OC EA N G E O L O G Y OCEANIC LAVA

Steam mixes with surf as lava from Kilauea Crater reaches the Pacific Ocean on the south shore of Hawaii. Basaltic lava such as this makes up the oceanic part of Earth’s crust.

40

OCEAN GEOLOGY

The Formation of the Earth THE EARTH STARTED TO FORM MORE THAN

4,500 million years ago in a disk of gas, dust, and ice around the early Sun. This protoplanetary disk, as it is known, was held in orbit by the gravitational field of the young star. Gravitational attraction between dust particles in the disk produced small rocks, and collisions concentrated the rocks into several rings. The most densely populated rings went on to form the planets of the Solar System.

EARLY SOLAR SYSTEM

Birth of the Earth

The early Solar System contained a disk of dust, ice, and gas, from which the rocky inner planets and gaseous outer planets formed.

small pieces of rock and ice pulled together by gravitational attraction

planetesimals start to form in protoplanetary disk around Sun

Initially, the rocks within each ring drifted together, due to their mutual gravitational attraction, in a process known as cold accretion. The largest bodies in each ring attracted the most material and grew to form objects larger than 0.7 mile (1 km) across, called planetesimals. Planetesimals are loose collections of rock and ice, with a uniform structure. As the mass of a planetesimal grows larger, it exerts a stronger gravitational pull, becoming more tightly held together and attracting nearby rocks with greater force. Collisions between planetesimals broke them apart or grouped them together. In the inner Solar System, the planetesimals in each orbiting ring came together to form much larger objects, called protoplanets, and these later collided to form the rocky planets. The Earth was born in this way about 4.560 million years ago.

1 COLD ACCRETION

Under gravity, pieces of rock and ice coalesced. Material sharing the same orbit around the Sun clumped together to form planetesimals.

3 HEAVY BOMBARDMENT

Each growing protoplanet attracted more planetesimals, which impacted through more energetic, high-speed collisions. Finally the protoplanets themselves underwent a series of collisions to form the rocky planets, including Earth.

2 PROTOPLANET

By attracting more clumps of rock and ice, and through many collisions, planetesimals grew into protoplanets. As the size of these increased, gravity smoothed out their surfaces.

rocks accelerate toward primordial Earth

impacts generate surface heat and local melting

Internal Heat The early Earth was hot but mostly solid, although with a partially molten surface, and had a fairly uniform internal composition.Today, it has layers of different compositions, including a dense, partially liquid core of iron and nickel.The transition may have its roots in several different energy sources. Localized surface melting would have occurred when the kinetic energy of incoming rocks was converted to heat during impacts. More significant heat sources would have been the decay of radioactive elements in the interior rocks and the heat released by the Earth’s contraction under the force of its own gravity—a process that led to an event called the iron catastrophe (see below). Impact with a sufficiently large body might have released enough heat to melt the Earth’s interior, and this may have happened more than once.

impact of Mars-sized body leads to total melting

MOON FORMATION

It is thought that early in Earth’s history, it was struck by a large protoplanet, creating the Moon, tilting the Earth’s axis of rotation, and leaving it with a slightly eccentric orbit.

INTRODUCTION

THE IRON CATASTROPHE

material ejected during collision later cooled and coalesced to form the Moon

1

As the Earth grew larger, the strength of its gravitational field increased, which in turn attracted more material.

2

Eventually, the gravitational field was strong enough to cause the Earth to contract, converting gravitational potential energy into heat.

3

Enough heat was released to melt the iron contained in the Earth’s rocks, allowing it to flow down to the center of the Earth.

4

The sinking of large amounts of iron released further heat, enough to melt the entire interior of the planet in the event called the iron catastrophe.

THE FORMATION OF THE EARTH

41

A LAYERED EARTH

Convection and Differentiation After the interior of the Earth melted, its heaviest constituents were able to sink to the center and the lighter ones to rise toward the surface. One-third of the planet’s mass pooled at the center and formed a dense core consisting mainly of iron, the heaviest of the common elements making up the Earth. The core became the hottest part of the planet, up to 11,700˚F (6,500˚C), and a source of heat for the molten rocks above. Most materials expand as they are heated, becoming less dense and more buoyant. This is the basis of convection, which provided a mechanism for carrying heat and material from the interior of the Earth toward the surface.Vigorous convection cells carried hot, buoyant material upward, where it lost heat by conduction near the surface, before sinking again. Lighter materials such as aluminum were left behind at the surface, forming a thin crust. In this way, the Earth became differentiated into layers of different chemical composition: a metallic core, a rocky mantle, and a buoyant crust. This occurred as early as 4,500 million years ago.

The early Earth had a uniform composition but melting allowed chemical “zoning” to develop. convection carries internal heat to surface

lighter materials rise up through semi-fluid mantle

carbon dioxide

water vapor

heavy materials sink to form dense core nitrogen

ATMOSPHERE AND OCEAN

The lightest materials of all, gases and water, were expelled from the interior to form the outer atmospheric and ocean layers at an early stage in the Earth’s history.

The Earth Today The Earth’s interior is now split into three chemically distinct layers, which can be further differentiated by changes in their physical properties due to temperature and pressure variations with depth. The core consists of an iron-nickel alloy, with some impurities, at a temperature of 7,200–11,700˚F (4,000–6,500˚C). Iron in the inner part of the core has solidified under the immense pressure, but the outer part is still a free-flowing liquid. The mantle of silicate rock surrounding the core has also solidified, but a form of convection called “solid-state creep” still takes place, with material in the lower mantle moving a few inches per year. The upper mantle, within about 255 miles (410 km) of the surface, is a more easily deformed “plastic” region. Above it floats a thin crust enriched in lighter elements, with average thickness ranging from 5 miles (8 km) beneath the oceans to 28 miles (45 km) beneath the continents. INSIDE THE EARTH

Earth has a layered internal structure, the main layers being the core, mantle, and crust. The density and temperature of the layers increases with depth. Heat from the core flows through the mantle, eventually reaching the cooler crust, where it escapes.

atmosphere

the transition zone is slightly denser than the upper mantle and forms a distinct layer between upper and lower mantle reservoir of magma (hot, melted rock) under Yellowstone Park, on North American Plate

hotspot under Hawaii, probably caused by a plume of hot material rising from deep in the mantle

liquid outer core solid inner core

lower mantle

upper mantle

consisting of the uppermost layer of the upper mantle together with overlying crust, the rigid lithosphere makes up tectonic plates

continental crust

the Chile Rise is a ridge marking the divergence of two tectonic plates, associated with upwelling of hot material from upper mantle

INTRODUCTION

oceanic crust

42

OCEAN GEOLOGY

The Origin of Oceans and Continents EARTH’S OCEANS FORMED MORE THAN

4 billion years ago, mainly from water vapor that condensed from its primitive atmosphere but also from water brought from space by comets. Initially, after acquiring a layered internal structure, the Earth had a uniform crust that was enriched in lighter elements and floated on an upper mantle made of denser materials. Later, the crust became differentiated into two types as continents began to form, made from rocks that were chemically distinct from those underlying the oceans.

zircon crystals, among the earliest continental crust materials ZIRCON primitive continental crust thickens above sinking mantle flow, without mantle interference

Continental Crust The continents include a wide range of rock THE OLDEST ROCKS types, including granitic igneous rocks, sedimentary These sedimentary rocks on Baffin Island rocks, and the metamorphic rocks formed by the lie on the Canadian alteration of both. They contain a lot of quartz, a Shield. The stable mineral absent in oceanic crust. The first continental continental shields rocks were the result of repeated melting, cooling, contain the world’s most ancient rocks, and remixing of oceanic crust, driven by volcanic activity above mantle convection cells, which were which are around 4 billion years old. much more numerous and vigorous than today’s. Each cycle left more of the heavier components in the upper mantle and concentrated more of the lighter components in the crust. The first microcontinents grew as lighter fragments of crust collided and fused. Thickening of the crust led to melting at its base and underplating with granitic igneous rocks. Weathering accelerated the process of continental rock formation, retaining the most resistant components, such as quartz, while washing solubles into the ocean. basaltic lava

rift

basalt sheets (dikes) sediment ocean surface

ocean crust

gabbro peridotite

lithosphere

Moho asthenosphere

magma rises to surface

top layer of upper mantle

INTRODUCTION

OCEAN-FLOOR STRUCTURE

Three layers of basalt in the crust (basaltic lava, dikes, and gabbro) are separated from the mantle by the Mohorovicˇic´ discontinuity (the Moho). The top layer of the upper mantle is fused to the base of the crust to form the rigid lithosphere, which makes up tectonic plates.The asthenosphere is the soft zone over which the plates of the lithosphere glide. MANTLE ROCKS

Peridotite is the dominant rock type found in the mantle, consisting of silicates of magnesium, iron, and other metals. Sometimes it is brought to the surface when parts of the ocean floor are uplifted, as here in Newfoundland, Canada, or as fragments from volcanic activity.

sedimentary rocks

primitive oceanic crust

volcanic activity adds igneous rocks to surface above rising flows

Oceanic Crust The oceanic crust has a higher density than the continental crust, making it less buoyant. Both types of crust can be thought of as floating on the “plastic” upper mantle, and the oceanic crust lies lower due to its lower buoyancy. It is relatively thin, with a depth of never more than 7 miles (11 km), compared with a thickness of 15–43 miles (25–70 km) for most continental crust. It consists mainly of basalt, an igneous rock that is low in silica compared with continental rocks, and richer in calcium than the mantle. Basalt lava is created when hot material in the upper mantle is decompressed, allowing it to melt and form liquid magma. The decompression occurs beneath rifts in the crust, such as those found at the mid-ocean ridges, and it is through these rifts that lava is extruded onto the surface to create new ocean crust.

THE ORIGIN OF OCEANS AND CONTINENTS DEVELOPMENT OF CONTINENTAL CRUST

Modification of the crust above rising mantle flows was delayed by the continuous intrusion of mantle basalt, resulting in the greenstone belts found today at the heart of each continental shield. greenstone belts above rising mantle flow basalt continuously intrudes from mantle

crust pulled apart by convective motion in mantle

43

BANDED IRON

Water and Atmosphere

Known as a banded-iron formation, this layered rock contains iron oxides that formed as the oxygen content of early oceans increased.

During the process of differentiation, volatile materials were expelled from Earth’s interior by volcanic activity. The lightest gases, such as hydrogen and helium, would quickly have been lost to space, leaving a stable atmosphere of nitrogen, carbon dioxide, and water vapor. Some of the water vapor would have condensed to form liquid water, and it seems there was a significant ocean earlier than 4 billion years ago. Some meteorites contain 15-20 percent ocean water from water and the early Earth is thought volcanic eruptions and comet to have had the same composition, impacts providing an ample source for the early ocean. More water arrived with impacting comets. It was in the ocean that free oxygen first appeared, with the arrival traces of early of photo- synthesizing life around 3.5 billion years ago. meteorite and comet

rivers erode and transport sediment

bombardment gradually erased

THE EARLY EARTH mantle vigorous convection cells in upper mantle

Earth had deep oceans from an early stage, with volcanoes and an increasing area of continental crust standing above the surface. The ocean became salty as weathering of surface rocks added minerals to the water.

rifts occur when fragments of crust move apart

volcanic eruptions add gases and water vapor to atmosphere

liquid outer core

solid inner core

This radar image shows volcanoes formed from andesite lava, whose composition is intermediate between oceanic and continental rocks.

INTRODUCTION

ANDEAN VOLCANOES

44

OCEAN GEOLOGY

The Evolution of the Oceans spreading ridge

EVER SINCE THE ATLANTIC COASTS OF SOUTH AMERICA

and Africa were accurately charted, it has been apparent that they match like the pieces of a jigsaw puzzle. We now know that the continents move, that they were once joined together, and that today’s oceans arose when the landmasses split apart. The evolving oceans have modified the global climate, and sea level has fluctuated in response to climate change and geological factors.

continent carried on plates

1. CAMBRIAN (500 MYA)

Plate Tectonics

The remains of the first supercontinent, Rodinia,

were scattered, with the largest piece, Gondwana, The numerous convection cells (see p.41) that gave rise to the lying in the south. The Iapetus Ocean separated first fragments of continental crust gradually gave way to fewer, Laurentia (North America) from Baltica (northern convection larger-scale convection cells as the mantle cooled. The continental Europe). The Panthalassic Ocean occupied cell drives fragments became consolidated into larger areas, and rifts most of the Northern plate motion Hemisphere. formed at the thinnest parts of the ocean crust, splitting it into large plates. When the density of the oceanic and continental plates became PANTHALASSIC OCEAN sufficiently different, the oceanic crust PLATE MOVEMENT sank where it met the more buoyant Crustal plates move continental crust, creating subduction around under the zones. Since then, the evolution of influence of convection LAURENTIA cells, which probably the oceans and continents has been reach deep down dominated by plate tectonics (see SIBERIA to the boundary pp.48–49). As the plates move, they between the outer IAPETUS carry the continents with them, with core and the mantle. OCEAN oceans opening and closing in between. BALTICA GONDWANA subduction zone

“ancestral” North Atlantic lies between North America and Europe

SIBERIA

PANTHALASSIC OCEAN

scattered remnants of Rodinia

2. DEVONIAN (400 MYA) AUSTRALIA

EURAMERICA

RHEIC OCEAN

GONDWANA

The Rheic Ocean opened when a string of islands, which were to become western and southern Europe, broke away from Gondwana and moved toward Euramerica, closing the Iapetus Ocean in the process.

shallow continental -shelf seas Ural Mountains

southern Europe joins Euramerica (Laurentia and Baltica) as Iapetus Ocean closes

first plants on land form vegetated areas

SIBERIA

PANTHALASSIC OCEAN

PALEOTETHYS SEA

INTRODUCTION

Through the Ages As Earth’s plates have moved around, largely driven by the spreading ridges and subduction zones of the rapidly recycling oceanic crust (see p.48), continents have come together and moved apart—periodically grouping together to form “supercontinents.” The German scientist Alfred Wegener proposed that 250 million years ago (mya) there was a supercontinent called Pangaea, centered on the equator and surrounded by one great ocean. It seems there was another grouping about 1 billion years ago called Rodinia, and perhaps an earlier grouping before that. Each time the continental landmasses have come together, they have eventually been broken apart as deep rifts opened up in their interiors, as is happening today in the Red Sea and the East African Rift. Computer models of the crustal fragments and the locations of spreading and subduction have allowed fairly reliable reconstructions of the geography of earlier times back to 500 million years ago.

PANGEA SOUTH AMERICA

extensive deserts

AUSTRALIA

AFRICA

GONDWANA southern ice cap covers most of South America, Africa, and Australia

3. CARBONIFEROUS (300 MYA) As the supercontinent Pangaea came together, continental masses stretched from pole to pole, almost encircling the Paleo-Tethys Sea to the east. Today’s coal seams were laid down in swampy forests along the shores of equatorial shelf seas. An extensive ice cap built up as Gondwana moved over the South Pole.

KEY

subduction zone spreading ridge outline of modern landmass

THE EVOLUTION OF THE OCEANS

45

Epicontinental Seas

PEOPLE

ALFRED WEGENER

At most times in the past, sea levels have been higher than they are today. This has given rise to shallow, tideless bodies of water called epicontinental seas covering extensive parts of the continental interiors. These were quite unlike the deep ocean basins and continental-shelf seas familiar to us today. The area of dry land was sometimes reduced to half its current extent by these seas, which were often very salty, low in oxygen, and devoid of life. They could isolate parts of continents, causing populations of living things to evolve separately. Epicontinental seas also affected the climate: their high salinity produced downwelling (see p.60) of dense water into adjacent equatorial oceans, in contrast to the polar downwelling that dominates the deep-ocean circulation today.

Alfred Wegener (1880–1930) was a German scientist with interests in astronomy, meteorology, and geology. In 1915 he presented the theory of continental drift to explain the presence of identical rocks on opposite sides of the Atlantic Ocean and tropical plant fossils in the Arctic Circle. His ideas were not accepted until seafloor spreading was discovered, providing a mechanism to explain his theory.

SHALLOW WATER

4. JURASSIC (150 MYA)

Conditions on the shore of North America’s Western Interior Seaway 100 million years ago may have been similar to the shallow lagoons of the Bahama Islands today (right).

central Atlantic starts to open

The Paleo-Tethys Sea closed as future parts of central Asia broke away from Gondwana and moved north, with the Tethys Ocean opening up behind them. The central Atlantic was opening, splitting Pangaea into northern and southern components.

LAURASIA NORTH AMERICA

PAC I F I C OCEAN

ASIA

EUROPE

TETHYS OCEAN

AFRICA SOUTH AMERICA

GONDWANA AUSTRALIA

opening of north Atlantic splits apart Europe and North America

ANTARCTICA

rifting signals creation of floor of modern Pacific Ocean

Western Interior Seaway

high sea levels

ARCTIC OCEAN

polar ice cap lost NORTH AMERICA

ASIA EUROPE

5. CRETACEOUS (100 MYA) The break-up of Gondwana started with India, Africa, and Antarctica rifting apart. This also started the closure of the Tethys Ocean. The opening of the south Atlantic soon followed, Europe separated from North America, and the Arctic Ocean opened over the North Pole.

PAC I F I C OCEAN SOUTH AMERICA

INDIA AUSTRALIA

Turgai Seaway

ANTARCTICA

Gondwana breaks up

Isthmus of Panama yet to close

remnants of Tethys Ocean EUROPE

ASIA

6. EOCENE (50 MYA) AFRICA INDIA

SOUTH AMERICA

INDIAN OCEAN AUSTRALIA

Antarctic ice cap begins to form

ANTARCTICA

India continued its rapid movement north, which would end with the uplift of the Himalayas when it hit Asia. Africa’s convergence with Europe closed the western Tethys Ocean. Australia and South America both separated from Antarctica, allowing the establishment of the Circumpolar Current that isolated Antarctica from equatorial heat flow. Australia moves north

INTRODUCTION

ATLANTIC OCEAN PAC I F I C OCEAN

TETHYS OCEAN

AFRICA

46

OCEAN GEOLOGY

Currents, Continents, and Climate Along with the atmosphere, the oceans are the means by which heat is redistributed around the Earth. Most energy arriving from the Sun is absorbed as heat near the Equator. It is then redistributed to colder regions. About 40 per cent of the heat reaching the poles from the Equator comes via ocean currents. The pattern of circulation in the oceans therefore has a large influence on the Earth’s climate (see pp.66–67). As continents, oceans, and currents have shifted through geological time, major climate changes have occurred. Conversely, warmer and colder periods affect sea level and the extent of seas.There is even speculation that the ocean froze to a depth of 2,000m (6,500ft) in places during a series of “snowball” events 775–635 million years ago, and possibly earlier, each event lasting up to 15 million years.

During snowball events, global glaciation would have left only the peaks of the highest mountains free of ice, as is the case today in Antarctica.

Greenhouse to Icehouse

MESOZOIC CURRENTS

100 million years ago, ocean currents flowed through a continuous seaway from the Tethys Ocean in the east, through what is now the Mediterranean, the Central Atlantic between North and South America, and into the Pacific in the west.

During the Mesozoic Era (252–65 million years ago) the climate was warmer than it is today, with a more even temperature distribution and no polar ice caps. Ocean currents freely flowed around the Equator, absorbing energy as they went, and carried heat to higher latitudes. The transition from this “greenhouse” climate to today’s cooler “icehouse” is due to shifts in ocean currents following the breakup of Gondwana. When the other continents moved north, the Antarctic was surrounded by the Circumpolar Current, blocking heat flow from the Equator. Equatorial flow between the oceans finally stopped when the Isthmus of Panama closed 5–3 million years ago. Antarctica now lies over the South Pole, allowing snow to accumulate into a thick ice cap, which reflects energy rather than absorbing it.

TODAY’S CIRCULATION

Today, equatorial ocean currents are blocked by landmasses, and the South Circumpolar Current is the strongest current, blocking heat flow to the South Pole. The polar regions are colder.

English Channel land bridge

Beringia land bridge

Greenland Ice Sheet Cordilleran Ice Sheet

Laurentide Ice Sheet

Patagonian Ice Sheet

Gulf of Persia dry Siberian Ice Sheet

Scandinavian Ice Sheet

sea ice

Antarctic Ice Sheet

INTRODUCTION

SNOWBALL EARTH

Sunda land bridge

Sahul land bridge

Yellow Sea dry

LAST GLACIAL (21,500 YEARS AGO)

Earth’s climate swings between ice ages and warmer periods over cycles lasting 100,000 years or more. Within ice ages, there are colder periods called glacials and warmer periods called interglacials. During glacials (the last of which peaked 21,500 years ago), the world’s ice-sheets expand, lowering global sea levels and revealing land bridges.

18/64 16/61

PRESENT LEVEL AT 0

20/68

tac eou s Pal eog e ne Ne og ene SEA LEVEL M/FT

22/72

14/57 300/980

12/54 TEMPERATURE ˚C/˚F

change of 100–200m (330–655ft) over a few tens of thousands of years. The rate of sea-floor spreading also affects global sea levels and has outweighed climatic factors at some times. Faster-spreading ridges reduce the volume of the ocean basins as the younger, hotter crust rises higher, causing sea levels to rise (see p.88). Local changes also occur as a result of crustal movement.

MEDITERRANEAN BASIN HISTORY

100/330 0/0

0

50

100

150

200

250

300

350

400

450

-100/-330 500

542

Sea level has constantly changed through history, being up to 400m (1,300ft) higher in the past. One of the factors controlling sea level is the global climate. Thermal expansion of ocean water increases global sea level by about 7.5cm (3in) for every 1˚C (1.8˚F) increase in temperature. The transfer of water between ice caps and the oceans during glacial cycles accounts for a global

200/660

10/50

47

Sea-level Change

Cre

Ca mb ria n O rd ovi c i an Sil uri an De von ian Ca rbo nif ero us Per mi an Tria ssi c Jur ass ic

THE EVOLUTION OF THE OCEANS

MILLIONS OF YEARS AGO

TEMPERATURE AND SEA LEVEL

Over the last 100 million years, climate has controlled sea levels, and these (in blue on graph) have dropped as the climate has cooled (temperature in yellow). At other times, low sea levels were due to reduced rates of sea-floor spreading.

The Mediterranean was isolated from the Atlantic by the closure of the Strait of Gibraltar five million years ago, and evaporated to a salty desert.

1

21,000 years ago, sea levels were 3 100,000 years ago, water from melting 120m (390ft) lower than they are today ice started to flood the continental due to water being locked up in ice caps shelves exposed during the glacial, at the height of the last glacial. leaving today’s familiar shoreline.

2

Sedimentary Basins BASINS AND OILFIELDS

Sedimentary basins are found on the continental shelves and adjacent ocean floor, but also well inland where areas were once covered with water.

AT L A

PA C I F I C

N

OCEAN

T

PA C I F I C

IC

O

KEY

OCEAN

AN

onshore sedimentary deposits

CE

Most of the world’s sedimentary rocks were laid down in water over continental shelves or in inland seas. The movements of the continents and changes in sea level have determined where this deposition occurred at particular times, and many former marine sedimentary basins are now far inland. Oil and gas deposits are found in marine sedimentary rocks, the result of animal and plant remains decomposing and then being buried and compressed. About 30 per cent of the world’s oil and gas production comes from offshore fields, but many offshore basins remain to be explored.

INDIAN OCEAN

offshore sedimentary deposits Oil and gas deposits

SOUTH

ERN OCEAN

During glacials, sea ice forms at lower altitudes than it does today. This scene may have been typical of the shores of western Europe 21,000 years ago.

INTRODUCTION

GLACIAL COAST

48

OCEAN GEOLOGY

Tectonics and the Ocean Floor THE THEORY OF PLATE TECTONICS HAS REVOLUTIONIZED

geology over the last half century, explaining many of the Earth’s physical features. Tectonic plates are huge fragments of the Earth’s lithosphere, which consists of the crust fused with the top layer of the upper mantle. They move over a more deformable layer of the mantle called the BASALT asthenosphere. Plate motion builds mountain ranges, but plateThe ocean floor is largely made of basalt, a fine-grained igneous rock tectonic processes are perhaps most clearly seen on the derived from the upper mantle. ocean floor, where most plate boundaries are found. It is a dense rock due to a high proportion of iron and magnesium. hotspot produces volcanic activity mid-ocean ridge lithospheric plate pushed away from ridge

rising mantle plume forms hotspot at surface

Recycling Ocean Crust The oldest rocks on the ocean floor are 180 million years old. This is young compared with the oldest continental rocks, which date from about 3.8 billion years ago. While the continental crust has been steadily accumulating throughout the Earth’s history, it seems the oceanic crust is created and destroyed rather quickly. It is created at the mid-ocean ridges from hot material rising in the mantle, and then spreads away from the ridges, before eventually being recycled into the mantle at subduction zones. Continental crust is always less dense and more buoyant than oceanic crust, so where they meet, it is the oceanic crust that gives way, sinking (subducting) back into the mantle.

AGE OF THE OCEAN FLOOR

The age of the ocean floor increases away from the spreading ridges where new crust is forming. The map below shows the East Pacific Rise to be the fastestspreading ridge, since it is flanked by the broadest spread of young rock (shaded red and orange).

incipient mantle plume

convection cell

oceanic lithosphere descends at subduction zone

MANTLE CONVECTION

Convection cells in the Earth’s mantle are the driving force behind plate tectonics. The cycle of hot material rising, cooling, spreading out, and sinking pushes and pulls the lithospheric plates around.

INTRODUCTION

Plate Boundaries

KEY ocean ridges at divergent plate boundaries direction of plate movement

The boundaries of a tectonic plate may be divergent, convergent, or transform. At divergent boundaries, the crust is extended, thinned, and fractured by the upwelling of hot mantle material. The crust buoys up, producing a mid-ocean ridge, and lava is extruded through a central rift valley to create new oceanic crust. Seamount volcanoes may also arise (see p.174). magma Plates collide at convergent boundaries. rises from mantle Where oceanic lithosphere meets continental lithosphere, the crust on the continental side may be compressed and thickened, resulting in mountain-building. The oceanic lithosphere sinks beneath the lighter continental lithosphere, forming an ocean trench (see p.183), and volcanic activity occurs above the descending plate. Where slabs of oceanic lithosphere converge, the oldest, most dense is subducted and an arc of volcanic islands is formed parallel to the trench. Transform boundaries arise where plates are moving past each other. No plate is created or destroyed. They can occur where segments of a divergent boundary are offset, and extensive fracture zones can result.

transform plate boundary

144

age (millions of years) 154

89

127

54.8

65

24

33.5

1.8

5

0

undated

DIVERGENT AND TRANSFORM BOUNDARIES

At divergent boundaries, parallel ridges emerge as new ocean floor spreads out either side of an ocean ridge. A transform boundary arises when sections of the ridge are offset from each other.

continent compressed, forming volcanic mountains

movement of oceanic lithosphere

oceanic trench

movement of oceanic lithosphere

movement of continental lithosphere

CONVERGENT BOUNDARIES

Ocean lithosphere is destroyed by subduction at convergent boundaries. The subducting plate carries water with it, which allows the surrounding mantle to melt, forming explosive volcanoes above.

magma forms as plate descends

oceanic lithosphere subducted beneath continental lithosphere

oceanic crust

TECTONICS AND THE OCEAN FLOOR

Earthquakes and Tsunamis

49

DISCOVERY

Earthquakes are associated with all plate boundaries, but they are particularly frequent at convergent boundaries, such as subduction zones. Stress builds up at faults in the crust until it overcomes the strength of the rock and the fault slips. When this happens, a huge amount of energy can be released in a short time. The earthquake that produced the 2011 Tohoku Tsunami in Japan released 600 million times more energy than the Hiroshima atomic bomb. A tsunami may be triggered if an earthquake results in the uplift or subsidence of part of the seafloor. The water above suddenly rises or sinks, then flows to regain equilibrium. Surface waves radiate out at 310–497 mph (500–800 kph) and can quickly cross an entire ocean basin. surface waves spread out at high speed

waves spread in opposite directions

TSUNAMI ALERTS Tsunamis can be very destructive, so systems have been established to look out for their distinctive signs and give warning of their approach. These systems use networks of seismic stations to detect earthquakes, and automated deep-sea buoys with seafloor pressure sensors to confirm whether a tsunami has been generated. The prototype buoy pictured at right is destined for seismic monitoring off the Caribbean coast of Grenada.

waves of moderate size in deep ocean

water suddenly elevated above fault

SEISMIC SEA WAVES

Tsunami waves increase in size as they encounter shallow water near the shore. They can grow from 10 ft (3 m) in the open ocean up to 100 ft (30 m) in extreme cases at the coast. waves become tall and destructive in shallow water

shockwaves spread out from the earthquake in all directions

few buildings can survive the onslaught of a large tsunami

movement along fault causes uplift of seafloor

Hotspots and Island Chains The seafloor between plate boundaries is far from featureless.Volcanic island chains are found far from any plate boundary due to the presence of hotspots (deep-seated and long-lived zones of volcanic activity) in the mantle. Some hotspots, such as the one beneath Iceland, are associated with divergent plate boundaries, while others lie in the middle of oceanic or continental plates. Chains of volcanoes often trail away from mid-ocean hotspots, with the oldest volcanoes, long extinct, now lying far away from the hotspot. These hotspot tracks are aligned along the direction of motion of the overlying plate. They change direction when the plate motion changes and may be interrupted when a new spreading ridge opens up, as it has between India and the Réunion hotspot.

seawater moves in circular motions beneath each wave as it passes

Iceland Yellowstone Azores Bermuda Canary Is. Cape Verde Is.

Hawaii Is.

Galapagos Samoa Marquesas

Hoggar

Caroline Is.

Molokini Island is the tip of an extinct volcanic crater, part of the Hawaiian–Emperor chain of islands and seamounts that stretches across the north Pacific.

Cameroon Ascension Is.

VOLCANIC ISLAND

St Helena Réunion

Easter Is. Crozet Is.

Bouvet Is.

Kerguelen Is.

HOT SPOTS

Some hot spot tracks link to areas where huge amounts of basalt flooded from the hotspot onto the surface long ago. The Tristan da Cunha hotspot is linked to flood basalts on both sides of the south Atlantic Ocean.

KEY

Plate boundaries flood basalts

convergent

hotspot tracks

transform

hotspot

divergent uncertain

INTRODUCTION

Tristan da Cunha

ERUPTION OF A SUBMARINE VOLCANO

Much of the world’s volcanic activity occurs below the ocean surface. Occasionally, an undersea volcano that has been growing for millennia reaches the sea surface and produces a dramatic eruption—as can be seen here, in an event that occurred near Hunga Ha’apai, Tonga, in the southwest Pacific, in March 2009.

OCEAN WATER IS constantly in motion, and

not simply in the form of waves. Throughout the oceans, there is a continuous circulation of seawater, both across the surface and more slowly deeper down. Several related processes play a part in causing and maintaining these ocean currents. They include solar heating of the atmosphere, prevailing winds, the effect of Earth’s rotation, and processes that affect the temperature and salinity of surface waters. The various surface currents that are generated, some warm, some cold, have profound effects on climate in many parts of the world. Oceanic processes also play a part in the periodic climatic disturbances called El Niño and La Niña, and they help generate the extreme weather phenomena known as hurricanes and typhoons.

C I R C U L ATI ON A N D C L IM AT E SPIRALING STORMS

Two cyclones—spiraling areas of low atmospheric pressure accompanied by cloud—are visible in this satellite image of part of the North Atlantic, taken in late 2006. The cyclones are moving eastward to the south of Iceland, which can be seen at top center.

54

CIRCULATION AND CLIMATE polar easterly

Ocean Winds

polar-front jet stream—narrow ribbon of strong wind at high altitude at top of front

THE PATTERN OF AIR MOVEMENT

over the oceans results from solar heating of the atmosphere and Earth’s rotation. This pattern of winds is modified by linked areas of low and high pressure (cyclones and anticyclones), which continually move over the oceans’ surface. Near coasts, additional onshore and offshore breezes are common. These are caused by differences in the capacity of sea and land to absorb heat.

The Coriolis Effect

initial direction of air movement

The atmospheric cells cause north–south air movements. These are altered by the Coriolis effect. As the Earth spins, parcels of air at different latitudes in the atmosphere have different west-to-east velocities (air at the Equator moves fastest). When they change latitude by moving to the north or south, they retain these west-to-east velocities, which differ from those of air in the AIR DEFLECTIONS In the Northern Hemisphere, latitudes they move into. Hence, the air veers to the Coriolis effect causes all air movements to be the east (in the direction deflected to the right of of Earth’s spin) when their initial direction. In moving away from the the Southern Hemisphere, Equator and to the west they veer to the left. when moving toward it.

westerlies

polar northeasterlies

westerlies

northeasterly monsoon (Nov–Mar)

northeasterly trade winds

Tropic of Cancer

Intertropical Convergence Zone

INTRODUCTION

air descends in subtropical latitudes Hadley cell air rises at equator

northeasterly trade wind southeasterly trade wind

trade winds meet at Intertropical Convergence Zone

air descends at pole

DISCOVERY

air deflected to right

air deflected to left

Ferrel cell

southwesterly wind

CIRCULATION CELLS Solar heating causes the air in Earth’s atmosphere to The atmospheric cells cycle around the globe in three sets of giant loops, produce north–south called atmospheric cells. Hadley cells are produced by airflows. These are by Earth’s warm air rising near the equator, cooling in the upper modified spin, producing winds atmosphere, and descending to the surface around that blow diagonally. subtropical latitudes (30˚N and S). Then the air moves subtropical back toward the equator. Ferrel cells are produced by jet stream air rising around subpolar latitudes (60˚N and S), cooling and falling in polar-front jet stream the subtropics, and then moving toward the poles. Polar cells are caused by air descending at the poles and moving toward the equator.

Earth’s rotation

air rises in subpolar latitudes

direction of Earth’s spin

Atmospheric Cells

initial direction of air movement

polar cell

equator

Tropic of Capricorn

SATELLITE IMAGING Ocean winds are monitored by instruments called scatterometers, such as an instrument called ASCAT on the METOP-A satellite (right). A scatterometer is a radar device that can measure both wind speed and direction.

ASCAT antenna (one of three)

Prevailing Winds The winds produced by pressure differences and modified by the Coriolis effect are called the prevailing winds. In the tropics and subtropics, the air movements toward the equator in Hadley cells are deflected to the west. These are known as trade winds. They comprise the northeasterly trades in the Northern Hemisphere, and southeasterly trades in the south. At higher latitudes, the surface winds in Ferrel cells deflect to the east, producing the westerlies. In the Southern Hemisphere, these winds blow from west to east without meeting land. Those around latitudes of 40˚S are known as the Roaring Forties. In polar regions, winds deflect to the west as they move away from the poles. These are known as polar northeasterlies and southeasterlies. KEY

prevailing warm southeasterly trade winds

westerlies

southeasterly trade winds

southeasterlies

southeasterly trade winds

westerlies

southwesterly monsoon (Apr–Oct)

prevailing cool local warm local cool

PATTERN OF WINDS

Year-round, the winds over most oceans are trades or westerlies. An exception is the northern Indian Ocean—this has a monsoon climate, in which a seasonal switch in wind direction occurs.

55 LONG-HAUL SAILING

Winds can blow with a consistent strength and direction over large areas of ocean. Consequently, on long-haul sailing trips, the same basic sail settings can often be used for days on end.

air ascends from cyclone

Pressure-system Winds

warm air rising air descends into anticyclone low pressure at center

central area of high pressure cold air sinks

air spirals around central area of low pressure

cold air flows toward area of low pressure

air moving from high to low pressure deflected by Coriolis effect to form spiral

In any area of ocean where air sinks—often at subtropical latitudes—a zone of high atmospheric pressure, or anticyclone, develops. Where warm air rises, areas of low pressure, called cyclones or depressions, occur. These often develop near the equator and subpolar latitudes. Cyclones and anticyclones create linked, circulating wind patterns, which continually move and change. In the Northern Hemisphere, there is a clockwise movement of air around an anticyclone, and a counterclockwise motion CYCLONES AND ANTICYCLONES around a cyclone. This pattern is reversed in the Air moves from an area of Southern Hemisphere. Local pressure systems can affect high pressure toward one the general pattern of prevailing winds. In particular, of low pressure, but the cyclones move swiftly over the ocean and can produce Coriolis effect modifies this, producing circular winds. rapid changes in wind strength and direction. warm air cools at high altitude

Coastal Breezes

On warm coasts, there is often a noticeable drop in temperature from midday as a cool sea breeze blows in off the water. The breeze typically reverses in the evening and at night.

DAY AND NIGHT

Land heats up faster

Local winds, called onshore and offshore than water during the day. air heats up Warm air rises over the land and rises over cool air breezes, are generated near coasts, especially in land drawn in and draws in cold air from sunny climes. Onshore breezes—sometimes the sea. At night, the land called sea breezes—develop during the day. cools more quickly, These are caused by the land heating up more reversing the airflow. quickly than the sea, as both absorb solar radiation. This occurs because the sea absorbs ONSHORE BREEZE large quantities of heat energy with only a small rise in temperature, whereas the same amount of heat energy is cold air sinks air heats up likely to cause the land temperature to rise sharply (see p.31). cool air drawn and rises As the land warms up, it heats the air above it, causing the air to rise. over ocean seaward Cooler air then blows in from the sea to take its place. In the evening, and at night, the opposite effect occurs. At nightfall, the land quickly cools down, but the sea remains warm and continues to heat the air above it. As this warm air rises, it sucks the cooler air off the land, and so generates an offshore breeze. This is sometimes called a “land breeze.” OFFSHORE BREEZE

INTRODUCTION

BREEZY COAST

cold air sinks

TRIMMING THE SAILS

A crew sets their sails as they set off on the Sydney-to-Hobart yacht race. The course crosses the often stormy Bass Strait between Australia and Tasmania.

57

Ocean Yacht Racing

Racing Around the Globe Three of the most famous ocean yacht races are global circumnavigations. They go “round the right way” in the Southern Ocean (west to east, the same direction as the prevailing winds and currents). The Volvo Ocean Race, held every three years, is a team event and includes stops. The Velux 5 Oceans Race and Vendée Globe are Vendée Globe single-handed races, each held every Velux 5 Oceans four years. The Velux 5 is in stages, 2010–11 Volvo 2014–15 whereas the Vendée Globe is nonstop.

ATLANTIC OCEAN

Abu Dhabi

MULTIHULL RACING

TRIMARAN Most ocean yacht races are for monohull yachts, but a few are open to multihulls (catamarans and trimarans), while some are for multihulls only. Multihulls are faster than monohulls, and although easier to capsize, they stay afloat even when severely damaged. Here, the trimaran Foncia is sailing on just one of its three hulls during the 2005 Grand Prix de Fécamp, off Normandy, France.

YACHT CREWS

ALL HANDS ON DECK The crews for some races are large— in the Clipper Round the World Yacht Race there are typically as many as 18 on board at any one time. For this race, the crew, who are recently trained amateurs, participate in all duties on the yacht, including trimming sails, navigating, helming, cooking, and so on.

TURNED TURTLE In 1997, the lone British yachtsman Tony Bullimore capsized in the Southern Ocean and was trapped for five days in his upturned yacht before rescuers arrived.

HANGING ON The crew of the yacht Astra (shown here) risk being swept overboard, the greatest disaster that can befall a sailor. To assist recovery in this eventuality, crew members usually wear radio beacons. It is also usual to be attached to the boat via a safety harness in anything other than calm daylight conditions.

PACIFIC OCEAN Sanya

Itajai

INDIAN OCEAN

Cape Town SOUTHERN OCEAN

Auckland Wellington

RISKY BUSINESS

PACIFIC OCEAN Recife Salvador

CONTROL CENTER Technology is all-important in modern racing, including the use of electronic charts and global positioning systems. Here, Frenchman Marc Thiercelin prepares for the Vendée Globe 2005–06 in the control center on his yacht Pro-Form.

INTRODUCTION

Göthenburg Les Sables-d’Olonne Lorient Newport La Rochelle Charleston Lisbon Alicante

EQUIPPED TO WIN

HIGH-TECH AIDS

Ocean yacht racing is the sport of competitive sailing, held over long distances and in open water. These races range from short but robust challenges lasting a few days, such as the famous Fastnet Race off southwest England and the annual Sydney-to-Hobart race, to long, multi-stage, around-the-world races, which can involve up to 6 months at sea. Some races are multi-handers, with crews that can be as large as 20 or more per yacht; others are single-handers. The participants are typically highly experienced sailors.In multi-handed races, there will be a skipper/tactician, a navigator, and general crew whose responsibilities include sail changing and trimming. Solo racers have to do everything themselves. One race, the Clipper Round the World Yacht Race, is unusual in that its crew consists of amateurs, some with little previous sailing experience, who have paid to take part under the leadership of a professional skipper. To make races as equitable as possible, usually competing boats are identical or a handicapping system is used to adjust the times of different classes of boats. The use of computer technology is paramount in modern racing. Navigation is electronically assisted, and computers are employed to monitor and help optimize boat performance.Vast amounts of weather data are downloaded via the Internet during a race. An important skill is to be able to interpret this data, so as to know, for example, where the most wind is likely to be in the area ahead. Otherwise, doing well in a race is mainly down to tactics and seamanship— for example, knowing how to get the best out of a boat in both strong and light winds, or judging when best to tack (change course when sailing upwind).

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CIRCULATION AND CLIMATE

Surface Currents FLOWING FOR ENORMOUS DISTANCES

within the upper regions of the oceans are various wind-driven currents. Many join to produce large circular fluxes of water, called gyres, around the surfaces of the main ocean basins. Surface currents affect only about 10 percent of ocean water, but they are important to the world’s climate (see p.66), because their overall effect is to transfer huge amounts of heat energy from the tropics to cooler parts of the globe. They also impact shipping and the world’s fishing industries. direction of

Coriolis deflection wind

frictional wind drag

Wind on Water

resultant direction of water motion

When wind blows over the sea, it causes the upper ocean to move, creating a current. However, the water does not move in the same direction as the wind. Instead, it moves off at an angle—to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This phenomenon was first explained in 1902 by a Swedish scientist, Walfrid Ekman, using a model of the effect of wind on water now called the Ekman spiral. The model assumes that the movement of water in each layer of the upper ocean is produced by a combination of frictional drag from the layer above (or, in the top layer, from wind drag) and the Coriolis effect (see p.54). The model predicts that, overall, a mass of water will be pushed at right angles to the wind direction, an effect known as Ekman transport. N. Atlantic Drift

Labrador N. Equatorial

E. Greenland

Gulf Stream

drag imparted from layer above direction of water motion

water motion in this layer

EKMAN SPIRAL Canary

Somali

Agulhas Oyashio

Alaska

Kuroshio N. Pacific California N. Equatorial

MAIN CURRENTS

Equatorial Counter

This map shows all of the world’s main surface currents, both warm and cold.

S. Equatorial E. Australia W. Australia

Antarctic Circumpolar Peru

S. Equatorial

Benguela

S. Equatorial

Ocean Gyres

INTRODUCTION

north Pacific gyre

The combination of prevailing winds (see p.54) and Ekman transport produces large-scale, circular systems of currents known as gyres. All together there are five ocean gyres—two in each of the Atlantic and Pacific oceans and one in the Indian Ocean. Each gyre westerly winds consists of several named currents. Thus, the gyre in the north Pacific is made up of the Kuroshio northeast current in the west, the California current trade winds in the east, and two other linked currents. Water tends to accumulate at the center of these gyres—producing shallow equator “mounds” in the ocean. southeast trade winds south Pacific gyre

westerly winds

direction of gyre direction of wind

warm current cold current

Brazil

GYRE CREATION

In the north Pacific, the combination of westerly and trade winds, always pushing water to the right (by Ekman transport) produces a clockwise gyre. In the south Pacific, where winds push water to the left, a counterclockwise gyre is created.

drag

The direction of motion in each water layer results from a combination of the drag from the layer above and a deflection caused by the Coriolis effect. This diagram shows the Ekman spiral in the Northern Hemisphere. In the Southern Hemisphere, deflection is to the left of wind direction.

SURFACE CURRENTS

59

PEOPLE

BENJAMIN FRANKLIN The American statesman and inventor Benjamin Franklin (1706–90) made one of the earliest studies of an ocean current, publishing a map of the Gulf Stream’s course. He became interested in it after the British postal authorities asked him why American postal ships crossed the Atlantic faster than English ships. The answer was that American ships were utilizing an eastward extension of the Gulf Stream.

Boundary Currents The currents at the edges of gyres are called boundary currents. Those on the western side of gyres are strong, narrow, and warm—they move heat energy away from the equator. Examples of these currents are the Gulf Stream and the Brazil Current in the southwestern Atlantic. Eastern boundary currents are weaker, broader cold currents that move water back toward the tropics. Examples are the Benguela Current off southwest Africa and the California Current. At the gyre boundaries close to the equator are warm, west-flowing equatorial currents. Other currents feed into or out of the main gyres. These include, for example, the warm North Atlantic Drift, an offshoot of the Gulf Stream, and cold currents that bring water down from the Arctic, such as the Oyashio and East Greenland currents. WARM CURRENT

Satellite devices can detect phytoplankton levels in the water, which can be related to temperature. Here, yellow and red indicate high levels of plankton and the warm Brazil Current.

COLD CURRENT

In this satellite view, sea ice is visible flowing past the Kamchatka Peninsula in the cold Oyashio Current. Eddies within the current have produced spiral patterns in the sea ice.

Meeting of Currents In a few areas, warm and cold currents meet and interact. Examples include the meeting of the warm Gulf Stream with the cold Labrador Current off the eastern seaboard of the US and Canada, and the meeting of the cold Oyashio Current with the warm Kuroshio Current to the north of Japan. At these confluences, the denser water in the cold current dives beneath the water in the warm current, usually producing some turbulence. This can trigger an upward flow of nutrient-rich waters from the sea floor, encouraging the growth of plankton, and producing good feeding grounds for fish, sea birds, and mammals. SEA SMOKE

OPPOSING CURRENTS

INTRODUCTION

The warm Brazil Current on the left, and the colder Falklands Current on the right, each carry differently colored populations of plankton.

Dolphins cavort amid steep waves. The “sea smoke” is created when water vapor is added to cold air drifting across the boundary between cold and warm currents.

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CIRCULATION AND CLIMATE

Underwater Circulation

The most important causes of downwelling are thermohaline NORTH ATLANTIC DOWNWELLING ZONES processes (“thermo” means heat, and “haline” means salt), which At the important downwelling alter either the temperature or salinity of seawater. For example, sites shown here, warm where warm, salty water is carried by a surface current into the surface water meets colder Arctic Ocean, it rapidly cools when it meets colder, less salty, Arctic water, loses heat, polar water. As it cools, its density increases, and it sinks down. become denser, and sinks. Downwelling also occurs on some coasts. For example, winds blowing toward the equator on the western side of oceans push east-facing coast (Northern seawater toward land by Ekman transport (see p.58). Hemisphere) As it reaches the coast, it is forced down. Finally, downwelling also occurs beneath the NORTH mounds of water that accumulate in the middle of anticyclones (see p.55) and ocean gyres (see p.58). COASTAL DOWNWELLING

A wind blowing toward the Equator on the western side of an ocean, as here (left), pushes seawater toward the shore, where it sinks. wind blowing toward the equator

water sinks near coast

water pushed toward shore due to Ekman transport

water level is raised at center of anticyclone

KEY

Upwelling can occur in various situations, some of which are simply the reverse of the conditions that cause downwelling. For instance, winds blowing toward the equator on the eastern sides of oceans push seawater away from land by Ekman transport, so deeper water must upwell near the coast to replace it. Water rises toward the surface in the center of cyclones (the opposite of anticyclones, see p.55), and will also rise where surface waters tend to be pushed apart at boundaries between ocean gyres—for example, in some equatorial parts of the Pacific and Atlantic. Some seawater upwells to replace sinking, denser, water. An example occurs around Antarctica, where upwelling replaces superdense, cold, salty water forming and sinking under developing sea ice.

A

ic rct

cle cir

ICELAND

NORTH ATLANTIC OCEAN downwelling warm surface current loss of heat energy cold surface current downwelling zone

winds flow clockwise in Northern Hemisphere (counterclockwise in Southern Hemisphere)

water sinks due to effects of gravity

Upwelling

NLAND

Downwelling

Baffin Bay

A N A D C A

circulate deep below the surface. Subsurface currents are complex. Some are vertical, moving water upward and downward to and from the surface, processes called upwelling and downwelling. Surface and subsurface currents are all linked in a global pattern of deep-water circulation.

GREE

THE WATERS THAT MAKE UP EARTH’S OCEANS

accumulation of water at center Ekman transport pushes water toward center of anticyclone

DOWNWELLING IN AN ANTICYCLONE

In an anticyclone, the circular system of winds can push water into a central mound, where it sinks. west-facing coast (Northern Hemisphere)

water moves away from shore as a result of Ekman transport

wind blowing toward the equator NORTH

COASTAL UPWELLING

INTRODUCTION

water moves upward to replace the water moving offshore at the surface

A wind blowing toward the equator on the eastern side of an ocean, as here, pushes seawater away from the shore, causing upwelling near the coast.

PLANKTON-HARVESTER Where upwelling occurs, it brings large amounts of nutrients up from the sea floor. These encourage the growth of plankton, attracting planktongrazers such as this manta ray as well as smaller fish, whales, and other marine life.

UNDERWATER CIRCULATION

61

Deep-water Circulation downwelling of cold, salty water in north Atlantic

cold, dense water moves at depth through Atlantic

warm surface flow in South Equatorial Current

diffuse upwelling in Indian Ocean

Seawater circulates slowly through the deeper parts of the oceans, driven by water sinking in major downwelling zones, such as in the north Atlantic. Any specific mass of deep water has, at some time, sunk in one of these zones. Once it sinks, its properties, such as its salinity, remain stable for long periods—thus, every mass of deep water contains a “memory” of where it originally sank. By analyzing seawater samples from various parts of the deep oceans, it is possible to piece together the general pattern of deep-water flow. The indications are that there is a large-scale circulation involving all the oceans, called the global conveyor. A specific mass of seawater takes about 1,000 years to complete a lap of this circuit. diffuse upwelling in north Pacific Ocean

warm surface flow of North Equatorial Current in central Pacific

Atlantic water is joined here by more cold water formed near Antarctica

warm flow of Equatorial surface current through Indonesian archipelago

DISCOVERY

SEAL AID This deep-diving elephant seal is helping to gather information about underwater circulation in the south Atlantic. A measuring device—attached to its head with glue that sloughs off when the animal molts—collects data about temperature and salinity at varying depths. The information gained may also help to conserve elephant seal populations.

THE GLOBAL CONVEYOR

The conveyor starts with cold, salty water sinking in the north Atlantic. Moving south at depth, it flows around Antarctica, branching into the Indian and Pacific oceans, and returns to the surface by mixing with warmer waters above. Finally, warm surface currents return it to the Atlantic.

combined mass of cold water moves slowly around Antarctica, at depth

cold, dense water flows north at depth into the Pacific Ocean

Circulation Cells

INTRODUCTION

One type of circulation that affects only the upper 70 ft (20 m) of the ocean, but is more complex than either a simple horizontal or vertical flow of water, is known as Langmuir circulation. This is wind-driven and consists of rows of long, cylinder-shaped cells of water, aligned in the direction in which the wind is blowing and each rotating in the opposite direction from its neighbor—alternate cells rotate clockwise and counterclockwise. Each cell is about 30–160 ft (10–50 m) wide and can be hundreds of yards long. On the sea surface, the areas between adjacent cells where seawater converges are visible as long white streaks of foam, or congregations of seaweed, called windrows. The whole pattern of circulation LANGMUIR WINDROWS long streaks of foam on the was first explained in 1938 by an American These sea surface are the windrows of chemist named Irving Langmuir, after he Langmuir circulation cells. The crossed the Atlantic in an ocean liner. distance between windrow lines increases with the wind speed. It was subsequently named in his honor.

DRIVING THE ATLANTIC CONVEYOR

Sea-ice formation on the margins of the Atlantic and Arctic helps to drive the Atlantic Conveyor. Only the freshwater component is incorporated in the ice, leaving dense, salty water that sinks to the ocean floor.

Shutting Down the Atlantic Conveyor CAUSES AND EFFECTS OF SHUTDOWN

At present, warm surface water moving north from the equator replaces cold water that sinks in the north Atlantic. Winds flowing over the warm ocean absorb heat and transfer it to western Europe. An increase of fresh water in the far northern Atlantic could mean that cold water no longer sinks there, shutting down the system and chilling Europe.

CHANGES IN ARCTIC ICE COVER There is ample evidence from satellite surveys that the extent of summer sea ice in the Arctic Ocean is diminishing rapidly at a rate of about 14 percent per decade. Should the Atlantic Conveyor shut down, however, this trend would reverse—Arctic seas close to the Atlantic, such as the Greenland Sea and Barents Sea, would become iced over all year.

ARCTIC MARINE LIFE Any shutdown in the North Atlantic Drift—the extension of the Gulf Stream that brings warm water to northwestern Europe—could have a major effect on life in Arctic areas adjacent to the north Atlantic. Changes in the currents would interfere with plankton production, affecting the whole food chain. The likely drop in temperature would also drive out some species of fish and invertebrates, which include crabs, starfish, and sea urchins.

LIFE SUPPORT FOR THE OCEAN FLOOR INFLOWS

Changes in the Atlantic Conveyor

ARCTIC SEA ICE

Global warming, it has been suggested, might have

the paradoxical long-term effect of lowering temperatures in Europe. The basis on which this could happen would be a shutdown of the Atlantic Conveyor – a system of currents that, at present, keeps western Europe warm. Part of a worldwide pattern of connected currents, the Atlantic Conveyor has two main components. The first is a flow of warm surface water into the northeastern Atlantic in the North Atlantic Drift – an extension of the Gulf Stream. The second component is the sinking of cold, salty water in the far north and the subsequent deep-ocean flow of this water back toward the equator. The conveyor might shut down if the Arctic seas are flooded with fresh water as a result of melting sea-ice and increased river run-off caused by global warming. Since fresh water is less dense than salt water, surface waters in these regions would become less likely to sink – risking disrupting the conveyor. If this were to occur, Europe’s average temperature could fall. How likely is this to happen? Computer models suggest that the current increase in the flow of fresh water in the Arctic is not high enough to shut down the conveyor. The models also suggest that the flows will not reach high enough levels for at least a century. Although a weakening of the conveyor could occur over the medium term, the models suggest that the overall outlook in this time frame could still be warming, rather than cooling, over Europe.

63

THE MACKENZIE RIVER DELTA Increased flow in Arctic rivers such as the Mackenzie—caused by the melting of glaciers and permafrost—might contribute to a shutdown of the Atlantic Conveyor by flooding fresh water into the Arctic Ocean.

THE SCILLY ISLES Situated 30 miles (50 km) off the southwest tip of Great Britain, the Scilly Isles sit directly in the path of the North Atlantic Drift. As a result, they enjoy a subtropical climate and are a haven for plants from all over the world. If the Atlantic Conveyor ground to a halt, gardens such as these would become desolate as average temperatures plunged to about 9°F (5°C).

PRESENT CIRCULATION cold water moves south over ocean floor

END OF THE ATLANTIC CONVEYOR lid of less salty water over denser, saltier water winds absorb less heat from ocean, and transfer less warmth to Europe

warm Gulf Stream no longer flows into north Atlantic

INTRODUCTION

warm water flows north from equator, transferring heat northward

THE NORTH ATLANTIC DRIFT

winds absorb heat from ocean and transfer it to Europe

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CIRCULATION AND CLIMATE

The Global Water Cycle

GLOBAL WATER FLOW

Water enters the atmosphere mainly as a result of evaporation from the oceans and transpiration by plants. It condenses to form clouds and falls as rain and snow. On land, water moves downhill in rivers and glaciers. It soaks into the soil and rocks, and is stored in lakes and wetlands.

THE WORLD’S OCEANS DO NOT FORM

a self-contained system but continually exchange water with the atmosphere and landmasses through evaporation, cloud formation, precipitation, wind transport, and river flow. This complex of interconnected processes, which is ultimately driven by heat from the Sun, is called the global water cycle or hydrologic cycle. The cycle is made up of many smaller cycles, such as the formation and melting of sea-ice.

snow falls when moisture in cold air freezes at high altitude snow and ice accumulate on high mountains

clouds form as rising air cools and the water vapor it holds condenses water returns to land as rain when moisturecarrying clouds cool

winds blow moisture-laden clouds inland

evaporation of water from ocean, driven by solar heating

in summer, snow and ice melt, releasing fresh water

release of water by plants through transpiration

evaporation of moisture from the ground as a result of solar heating

rivers steadily transport water towards the ocean

eventually, downhill flow means rivers flow into the oceans

ocean water is salty because it contains dissolved nutrients

below a line known as the water table, the rock is saturated with water

water collects in hollows in the ground, forming freshwater lakes

water can flow downhill underground as well as above ground

cracks and holes in the rocks allow them to be filled with water

atmosphere and other 0.09%

INTRODUCTION

Earth’s Water Reservoirs

PLAYERS IN THE CYCLE

The sea, ice, mountains, and clouds all play a part in the global water cycle. This coastal scene is near Port Lockeroy in Antarctica.

Just under one-third of a billion cubic miles (1.4 billion cubic kilometers) of water exists on Earth. About 97 percent of this water is stored in the oceans as a component of salt water. The rest is fresh water. Of this, more than two-thirds is in the form of ice, locked up in the vast ice-sheets that cover Antarctica and most of Greenland, and in icebergs and sea-ice. Much of the rest is groundwater—contained in underground rocks—while a tiny amount (less than 1 part in 2,000) is water vapor in the atmosphere. Fresh liquid water on the Earth’s land surface, in lakes, wetlands, and rivers, makes up just 0.3 percent of all the world’s fresh water, or 0.02 percent of the total water. The Earth’s different water reservoirs have not always had the same relative sizes that they have today. For instance, during the ice ages, a higher proportion was locked up in ice, with less in the oceans.

ocean water 97%

fresh water 3.5%

surface fresh water 0.3% groundwater 30.1% rivers 2%

EARTH’S WATER

wetlands 11%

ice 69.5% lakes 87%

FRESH WATER SURFACE FRESH WATER

RELATIVE SIZES

Earth’s ocean water (the bulk of the rear cylinder, above) hugely exceeds its reservoirs of fresh water, and the relative proportion of fresh water found on the land surface is tiny.

65

Ocean Evaporation and Precipitation A total of 104,000 cubic miles (434,000 cubic kilometers) of water evaporates from the oceans per year. Of this, 95,500 cubic miles (398,000 cubic kilometers) falls back into the sea as precipitation (rain, snow, sleet, and hail). The remainder is carried onto land as clouds and moisture. Evaporation and precipitation are not evenly spread over the surface of the oceans. Evaporation rates are greatest in the tropics and lowest near the poles. High rates of precipitation occur near the equator and in bands between the latitudes of 45º and 70º in both hemispheres. Drier regions are found on the eastern sides of the oceans between the latitudes of approximately 15º and 40º. PEOPLE

SENECA THE YOUNGER In his book Natural Questions, the Roman statesman, dramatist, and philosopher Seneca the Younger (4 bc–ad 65) pondered why ocean levels remain stable despite the continuous input of water from rivers and rain. He argued there must be mechanisms by which water is returned from the sea to the air and land and proposed an early version of the hydrologic cycle to explain this.

Freshwater Inflow The 8,500 cubic miles (36,000 cubic kilometers) of water lost from the oceans each year by evaporation and transport onto land is balanced by an equal amount returned from land in runoff. Just 20 rivers, including the Amazon and some large Siberian rivers, account for over 40 percent of all input into the oceans. Inflows from the different river systems change over time as they are affected by human activity and climate change. For instance, global warming appears to have increased the flow from Siberian rivers into the Arctic Ocean, as water frozen in the tundra melts. These inflows lower the salinity of Arctic waters and may influence global patterns of ocean circulation (see p.63).

SIBERIAN RIVER AMUR FLOODING

Climate change is thought to have contributed to severe flooding of the Amur River in Northeast Asia in recent years (below). A color-enhanced satellite image (left) shows the engorged river in black; green areas are plant-covered land.

EQUATORIAL RAINSTORM

In some areas near the equator, as here in the tropical Pacific, annual rainfall is over 120 in (300 cm), compared to under 4 in (10 cm) in the driest ocean areas.

The Sea-ice Cycle

SEA-ICE FORMING

As sea-ice forms, it releases heat to the atmosphere and increases the saltiness of the surrounding water (by rejecting salt). These processes affect climate and the circulation of seawater.

INTRODUCTION

In addition to the overall global water cycle, there is a local seasonal cycle in the amount of water locked up as sea-ice. In the polar oceans, the extent of sea-ice increases in winter and decreases in summer. This has important climatic consequences, because sea-ice formation releases, and its melting absorbs, latent heat to and from the atmosphere; and because the presence or absence of sea-ice modifies heat exchange between the oceans and atmosphere. In winter, sea-ice insulates the relatively warm polar oceans from the much colder air above, thus reducing heat loss. However, especially when covered with snow, sea-ice also has a high reflectivity (albedo) and reduces the absorption of solar radiation at the surface. Overall, the sea-ice cycle is thought to help stabilize air and sea temperatures in polar oceans. Also, because it affects surface salinity, sea-ice formation helps drive large-scale circulation of water through the world’s oceans (see p.61).

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CIRCULATION AND CLIMATE

Oceans and Climate THE OCEANS HAVE A PROFOUND INFLUENCE

on the world’s climate, most strikingly in the way they absorb solar energy and redistribute it around the world in warm surface currents. Cold currents also produce local climatic effects, while alterations in currents are associated with climatic fluctuations such as SOLAR HEATING surface layers of the oceans El Niño (see p.68). The future behavior of the oceans is crucial The absorb about half the solar to the future course of climate change, as they are an important energy that reaches Earth. Currents move this from the store for carbon dioxide, the principal greenhouse gas. equator toward the poles at a rate of several billion megawatts.

Warm Currents Five or six major surface currents (see p.58) carry heat away from the tropics and subtropics toward the poles, giving some temperate regions a warmer climate than they would otherwise enjoy. A prime example is the effect of the warm Gulf Stream and its extension, the North Atlantic Drift, on Europe. The North Atlantic Drift carries heat originally absorbed in the Caribbean Sea and Gulf of Mexico across the Atlantic, where it is released into the atmosphere close to the shores of France, the British Isles, Norway, Iceland, and other parts of northwestern Europe. As the prevailing westerly winds blow this warmed air over land, these countries benefit from a milder climate than equivalent regions at similar, or even lower latitudes, on the western side of the Atlantic. For example, winter temperatures are typically BALMY BEACHFRONT higher in Reykjavik, the capital of Iceland, than in New York. Similarly, in the northwest Penzance, in southwest England, has a mild climate that supports Pacific, the Kuroshio Current warms the subtropical vegetation—the southern part of Japan, while in the extreme effect of the North Atlantic Drift southwest Pacific, the East Australian Current is to raise temperatures here by about 9˚F (5˚C). gives Tasmania a relatively mild climate.

INTRODUCTION

Cold Currents

STRAYING NORTH

In some instances, the climatic effect of cold currents is simply to produce a cooler climate than would otherwise be the case. For instance, the west coast of the US is cooled in summer by the cold California Current. Cold currents also affect patterns of rainfall and fog formation. In general, the various cold currents flowing toward the equator on the eastern sides of oceans—combined with upwellings of cold water from the depths in these regions— cool the air, reduce evaporative losses of water from the ocean, and cause downdrafts of drier air from higher in the atmosphere. Although clouds and fog often develop over the ocean in these areas (as what little moisture there is condenses over the cold water), these quickly disperse once the air moves over land.Thus, cold currents contribute to the development of deserts on land bordering the eastern sides of oceans, such as the Namib desert in southwestern Africa.

COAST OF NORTHERN CHILE

The cold Peru Current flows along the coast of northern Chile. It encourages the development of clouds and fog over the sea (visible above left in the satellite image) but also contributes to the extreme aridity of the coastal strip (left).

Most penguins live in Antarctica but, somewhat surprisingly, the world’s most northerly-living penguins inhabit the Galápagos Islands, on the equator. The islands have a cool climate— sea-surface temperatures in most years average 9˚F (5˚C) less than typical temperatures in the tropics, due to the cold Peru Current that flows up the west coast of South America.

OCEANS AND CLIMATE FORAMINIFERAN SHELL

Carbon in the Oceans

The oceans contain Earth’s largest store of carbon dioxide (CO2)—the main greenhouse gas implicated in global warming. Huge amounts of carbon are held in the oceans, some in the form of CO2 and related substances that readily convert to CO2, and some in living organisms. The oceanic CO2 is in balance with the atmospheric content of the same gas. For many years, the oceans have been alkaline, and acted as an important store for the excess CO2 released by human activity. Biological and chemical processes turn some of this CO2 into the calcium carbonate shells and skeletons of organisms, other organic matter, and carbonate sediments. However, the increasing CO2 concentration is beginning to acidify the oceans, threatening shell and skeleton formation in marine organisms, as acid tends to dissolve carbonates. Further, some scientists fear that the rate at which the oceans can continue to absorb CO2 will soon slow down, further aggravating global warming. CO2 released by plant respiration

CO2 absorbed by photosynthesis

CARBON CONVERSION

CO2 released from burning fossil fuels (right), after absorption into the oceans, can eventually end up in the shells of marine organisms in the form of carbonate. CO2 released by volcanic eruption

CO2 released by fossil-fuel burning

CO2 in rain weathers limestone

CO2 released by fossil-fuel burning

CO2 absorbed by photosynthesis by phytoplankton

CO2 released by land animal respiration

METHANE HYDRATE DEPOSIT

This substance is found as a solid on some areas of sea floor. There are concerns that ocean warming could release this into the atmosphere as methane gas, which traps more heat than CO2.

67

CO2 released by marine animal respiration

CO2 removed from storage by coal mining carbon from plant and animal remains stored in form of coal deposits

CO2 released by phytoplankton respiration

CARBON SOURCES AND STORES

At present, more CO2 is added to than subtracted from the atmosphere. Some of the excess is absorbed by the oceans, where some is held in solution and some incorporated into living organisms and sediments.

carbon released by decomposition of marine organisms

carbon released by decomposing phytoplankton

oil and gas

carbon in sediment turns into oil and gas

carbonate in sediment turns into limestone

The climate of San Francisco is influenced by exceptionally cold water, produced by upwelling, off the California coast. Fog is produced as westerly winds blow moist air over this cold water.

INTRODUCTION

GOLDEN GATE FOG

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CIRCULATION AND CLIMATE

El Niño and La Niña EL NIÑO AND LA NIÑA ARE LARGE

climatic disturbances caused by abnormalities in the pattern of sea surface temperature, ocean currents, and pressure systems. They are in the tropical Pacific Ocean. These disturbances have important repercussions for weather throughout the Pacific and beyond. Most scientists regard El Niño and La Niña as extreme phases of a complex global weather phenomenon called the El Niño–Southern Oscillation (ENSO).

descending air associated with high pressure and dry conditions

southeast trade winds

low-pressure system in western Pacific with rising warm, moist air and associated heavy rainfall

El Niño Events The Spanish term el niño means “the little boy” or “Christ child.” It originally denoted a warm current that was occasionally noticed around Christmas off Peru. Later it was restricted to unusually strong rises in temperature in the waters of the eastern Pacific, with a reduction in the upwelling of nutrient-rich waters that normally occur there. It is now used to mean a much wider shift in ocean and atmospheric conditions that affects the whole globe. El Niño events typically last from 12 to 18 months and occur cyclically, although somewhat unpredictably. On average, they occur about 30 times per century, with intervals that are sometimes as short as three years and sometimes as long as 10 years. Their underlying cause is not understood. TEMPERATURE PATTERNS

These satellite-generated images of the Pacific compare surface temperature patterns. Red and white indicate warm water; green and blue denote cooler water.

pool of warm water South Equatorial Current

upwelling of cold, nutrient-rich water

NORMAL PATTERN southeast trade winds reverse or weaken

descending air and high pressure brings warm, dry weather

A low-pressure system in the western Pacific draws southeast trade winds across from a high-pressure system over South America. These winds drive the South Equatorial Current, which maintains a pool of warm surface water in the western Pacific. low pressure and rising warm, moist air associated with heavy rainfall

warm water flows eastward, accumulating off South America

EL NIÑO PATTERN JANUARY 2011 (NORMAL)

upwelling blocked by warm water near surface

During an El Niño event, the pressure systems that normally develop in the Pacific, and the southeast trade winds, weaken or reverse. The pool of warm surface water extends from the western Pacific into the central and eastern Pacific.

DECEMBER 2009 (EL NIÑO)

INTRODUCTION

Effects of El Niño

GIANT WAVES

An El Niño event causes wetter-than-normal conditions, and floods, in countries on the western side of South America, particularly Ecuador, Peru, and Bolivia. These conditions may also extend to the southeastern United States. In other parts of the world, it causes drier conditions. Drought and forest fires become more common in the western Pacific, particularly in Indonesia and parts of Australia, but also in East Africa and northern Brazil. The warmer waters in the eastern Pacific cause a reduction in the Peru Current and reduced upwelling near the coast of South America. This reduces the level of nutrients in the seawater, which has a negative impact on fish stocks. Other effects include a quieter Atlantic hurricane season and an increase in the extent of sea ice around Antarctica. Japan, western Canada, and the western US typically experience more storms and warmer weather than normal. width of rings directly related to amount of growth 1746–47 El Niño ring

EVIDENCE OF AN HISTORICAL EL NIÑO

Increased tree growth can be linked to high rainfall that occurred during historic El Niño events. One of the rings in this sample has been linked to an El Niño in 1746–47.

During an El Niño event, storms become more frequent and violent in the central Pacific. These storms can produce gigantic waves, up to 33 ft (10 m) high, in Hawaii, as here on the island of Oahu.

CORAL BLEACHING

This small circular coral reef has suffered severe bleaching (whitening). El Niño events are often associated with bleaching caused by unusually high sea surface temperatures.

EL NIÑO AND LA NIÑA DISCOVERY

MONITORING The tropical Pacific is regularly monitored for temperature changes. The main monitoring methods are the use of satellites, which measure sea temperatures indirectly from slight variations in the shape of the ocean surface, and an array of instrumented weather buoys. INSTRUMENTED BUOY

Buoys such as this one, strung in an array across the equatorial Pacific, are used to make regular measurements of water temperature at varying depths.

La Niña Events La niña is Spanish for “the little girl.” A La Niña event is the reverse of an El Niño event. It is characterized by unusually cold ocean temperatures in the eastern and central equatorial Pacific, and by stronger winds and warmer seas to the north of Australia. La Niña conditions frequently, but not always, follow closely on an El Niño. Like El Niño, La Niña causes increased rainfall in some world regions and drought in others. India, Southeast Asia, and eastern Australia are lashed by rains, but southwestern US generally experiences higher temperatures and low rainfall. Meanwhile, northwestern states of the US pool of warm water positioned experience colder, snowier winters. farther west than La Niña is also associated with an normal increase in Atlantic hurricane activity. Overall, the effects of a La Niña event often tend to be strongest during Northern Hemisphere winters.

low-pressure system, positioned farther west than normal

South Equatorial Current

southeast trade winds

69

descending air associated with dry conditions and high pressure

upwelling of cold, nutrientrich water sea surface cooler than normal in eastern Pacific

LA NIÑA PATTERN

DROUGHT CONDITIONS

This water reservoir in Texas completely dried up during a severe La Niña-related drought that affected the southwestern US in 2011.

During a La Niña event, the area of low pressure in the western Pacific is farther west than normal, and the pool of warm surface water is also pushed west. Unusually cold surface temperatures develop in the eastern Pacific as the cold Peru Current strengthens off South America.

Teams of youths work to shepherd pedestrians across a highway in Peru flooded by heavy El Niño rains in 1998. This El Niño ravaged Peru, causing 250,000 people to abandon their homes.

INTRODUCTION

PERUVIAN FLOOD

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CIRCULATION AND CLIMATE

Hurricanes and Typhoons HURRICANES AND TYPHOONS ARE TERMS USED IN

different parts of the world for very similar weather phenomena. They are characterized by violent winds moving in a circular pattern over the ocean, dense bands of clouds, and rainfall. In the Atlantic they are known as hurricanes; those in the west Pacific are called typhoons. Similar phenomena elsewhere are called severe storms or cyclones. They start as a low-pressure system (depression) over warm oceans in the tropics, between latitudes 5° and 20°, and occur mainly in late summer. A R C T I C

DISTRIBUTION

Severe tropical cyclones start as depressions over warm oceans in the tropics. They move across the ocean surface for several days, causing huge damage on reaching land. Their paths are shown in the map above.

O C E A N

A

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PAC I F I C

A

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O C E A N

Development All tropical cyclones develop from the effects of the Sun warming the surface of a broad area of ocean and the air above it. This heating causes masses of warm, moist air to rise, creating a region of low pressure at the surface, and dense clouds above it. The low pressure sucks in more air, which spirals to the center, creating a circular wind system. As it grows stronger, becoming THREE DEVELOPMENT STAGES: HURRICANE SANDY, OCTOBER 2012 a tropical storm, it is pushed westward by the prevailing trade winds. In the Atlantic, a storm attains hurricane status once its winds exceed 74 mph (119 kph). Eventually, most of these violent storms move away from the equator— that is, to the north in the Northern Hemisphere. When one reaches land, it begins to 1 On October 23 a swirling mass of 2 By October 26, the cyclone has lose energy, as it is no longer warm, moist air rises over a tropical a spiral form, with a dense central fed by heat from the ocean. area of ocean, condensing into clouds. nucleus of clouds.

INTRODUCTION

cap of cirrus clouds over cumulonimbus that forms bulk of clouds

eyewall is a ring of destructive thunderstorms and rainbands around the eye

eye of the hurricane is a calm, cloud-free area of sinking air and light winds

high-level winds spiral outward

ascending warm, moist air created by solar heating of the ocean surface

INDIAN OCEAN

O C E A N

H E R N S O U T

KEY hurricanes severe cyclones typhoons

3

At full hurricane status on October 28, the cyclone has compacted and developed a clear central “eye.”

Structure A fully developed typhoon or hurricane is usually 185–370 miles (300–600 km) in diameter and 6–9 miles (10–15 km) high. At its center is a calm region of low atmospheric pressure, called the eye. Within the rest of the cyclone, winds spiral in an counterclockwise direction in the Northern Hemisphere and clockwise in the Southern Hemisphere (the difference is due to the Coriolis effect, see p. 54). Within an area surrounding the eye, called the eyewall, the air spins upward, forming dense clouds. The eye stays calm because the winds that spiral in toward it never reach the center. Radiating out from the eye and eyewall are well-defined bands of clouds, called rainbands.

HURRICANE STRUCTURE

sea surface rises at center of hurricane low pressure at water’s surface creates warm winds; these increase in speed toward the eye

OCEAN

N CEA C O TI

P A C I F I C

spiral rainbands can extend for hundreds of miles from the hurricane center cool, dry air sinking toward the ocean surface

A hurricane consists of the central eye, which can be 5–120 miles (8–200 km) across, the eyewall (a column of thick clouds, rain, and upward-spiraling winds), and the rainbands.

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STORM SURGE

Hurricane Frances hits Juno Beach, Florida, in September 2004. Classed as a Category 2 hurricane when it hit land, Frances caused a storm surge 6 ft (2 m) high, which ripped across highways and flooded homes and business premises.

HURRICANE CATEGORIES A classification system called the Saffir–Simpson Scale divides hurricanes into five categories. It is used to estimate the damage and flooding to be expected along a coast impacted by the hurricane. Wind speed is the determining factor in the scale. CATEGORY

WIND SPEED

Tropical Storm

39–73 mph (63–118 kph)

less than 3 ft (1 m)

Category 1 hurricane

74–95 mph (119–153 kph)

3–5 ft (1–1.5 m)

Category 2 hurricane

96–110 mph (154–177 kph)

6–8 ft (2–2.4 m)

Category 3 hurricane Category 4 hurricane Category 5 hurricane

111–129 mph (178–208 kph) 130–156 mph (209–251 kph) over 156 mph (251 kph)

9–12 ft (2.7–3.7 m) 13–18 ft (4–5.5 m) over 19 ft (5.8 m)

DISCOVERY

STORM CHASERS

LOCKHEED WP-3D ORION

This turboprop aircraft, equipped with a sophisticated array of instruments, is one of those used in hurricane study.

As it moves across the ocean, the low-pressure eye of a tropical cyclone sucks seawater up into a mound, which can be up to 12 ft (3.5 m) above sea level for a Category 2 hurricane or 25 ft (7.5 m) for a Category 5. When the cyclone hits land, the water in this mound surges over the coast in what is known as a storm surge. The surge may flood homes, wash boats inland, destroy roads and bridges, and seriously erode a section of coastline up to 95 miles (150 km) wide. These effects compound the devastation caused by high winds, which can topple unstable buildings, uproot trees, damage coastal mangroves, and bring down power lines. Human deaths are not uncommon, so coastal areas threatened by a severe cyclone are normally evacuated in advance. Offshore, the water movements associated with a storm surge can devastate coral reefs. In the Caribbean, branching corals that live near the surface, such as elkhorn WATERSPOUT corals, are particularly Waterspouts are vulnerable. Healthy tornados (narrow, whirling masses of reefs can recover from air) over the sea. such damage, although They are quite it can take 10–50 years commonly spawned depending on the around the edges of tropical cyclones. extent of injury.

CORAL DAMAGE

This colony of elkhorn coral was smashed by Hurricane Gilbert on Mexico’s Caribbean coast in 1988.

INTRODUCTION

The United States’ National Oceanic and Atmospheric Administration (NOAA) monitors Atlantic hurricanes using specially equipped aircraft. They fly into hurricanes to drop instrument packages, which radio back data.

HEIGHT OF SURGE

Coastal Effects

REDUCED TO TATTERS

Survivors stand among ruined houses in Tacloban, on Leyte island in the Philippines, after its destruction by Typhoon Haiyan and the accompanying storm surge.

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Typhoon Haiyan GENESIS

PATH OF DESTRUCTION

TRAIL OF DEVASTATION

The map below shows Haiyan’s path between November 5, when it reached the equivalent of a category 4 hurricane, and November 11, when it was downgraded to a tropical depression as it moved into China. Its most dangerous phase was reached on November 8, when it crossed the Philippines as a super-typhoon, equivalent to a Category 5 hurricane. These satellite images show Haiyan’s appearance as it centered over the Philippines (top) on Friday November 8, and as it moved into southern China (bottom) on Monday, November 11.

INFRASTRUCTURE DAMAGE The high level of destruction in urban areas, which included downed power lines and radio masts, blocked roads and interfered with relief efforts.

FLATTENED PALMS The typhoon’s effect on rural areas was equally terrible. This aerial view shows a destroyed coconut plantation and village on Leyte island.

FOOD DROPS The disaster left an estimated 1.9 million Filipinos in need of food, water, and shelter. Here, a Philippine Air Force crew drops sacks containing food supplies.

PACIFIC OCEAN

Nov 6–8 Category 5

Nov 9–10 Category 2

VIETNAM Nov 8–9 Category 4

PA L AU Nov 5 Category 4

RELIEF OPERATION

P H IL P P INE S

LAOS

MEDICAL AID Thousands needed medical assistance and urgent measures to combat spread of infectious diseases. Here, a child receives a measles vaccine.

INTRODUCTION

Nov 11 Tropical depression Nov 10–11 Tropical storm Nov 10 Nov 9 Category 1 Category 3

EVACUATION Warnings had been issued across a wide region to evacuate or seek safe refuge. Here, a Filipino child is being taken to board a military plane as part of an evacuation program.

DESTROYED COMMUNITY The destruction caused to parts of the central Philippines that Haiyan passed across was almost total. This aerial view shows the town of Guiuan in eastern Samar province.

Track of the Typhoon

CHINA

EYE OF THE STORM Haiyan originated around November 2 from an area of low pressure in the western Pacific. Over the next 3–4 days, it grew into a super-typhoon and developed a distinct “eye” at its center.

STORM SURGE By November 7, Haiyan was producing sustained winds of up to 168 mph (270 kph). The next day, it made landfall in the Philippines, where a storm surge pounded coastal areas.

LANDFALL IN PHILIPPINES

Typhoon Haiyan, known in the Philippines as Typhoon Yolanda, was an exceedingly powerful tropical cyclone that devastated the Philippines and some other parts of Southeast Asia between November 4 and November 11, 2013. It is the deadliest typhoon ever recorded in the Philippines, killing more than 6,000 people in that country alone. Haiyan is also the most powerful storm ever to hit land, and the fourth most intense tropical cyclone ever recorded in terms of highest sustained wind speeds. Most of the catastrophic destruction occurred in a central group of islands within the Philippines called the Visayas. Although wind speeds were extreme, the major cause of damage and loss of life was a storm surge, particularly hitting the eastern coasts of the islands of Samar and Leyte. The city of Tacloban, with a population of over 220,000, was almost completely destroyed. On November 10 and 11, Haiyan passed over Vietnam and southern China, by which time it had weakened to a tropical storm and then to a depression. Nevertheless, there was extensive flooding in some areas, thousands of homes were destroyed, and around 50 people were killed. Some climate scientists believe that global warming will increase the frequency of high-intensity tropical cyclones like Typhoon Haiyan. If this is the case, governments in affected countries will need to make provisions for dealing with similar-scale catastrophes more often in the future.

WAVES AND TIDES are two important

physical phenomena that affect every area of the oceans but tend to be most noticeable, and have their main effects, on or near coasts. Ocean waves are mostly wind-generated and vary from tiny coastal ripples, to the regular, rolling swell of the open ocean, to monster breakers on worldfamous surfing beaches. All waves transmit energy—when the waves reach land, this energy may be dissipated destructively, eroding coastlines, or constructively, building up features such as beaches. Tides are caused mainly by interactions between the Moon and Earth. As well as regular rises and falls in sea level, they can cause strong currents around coasts and, in some places, even more dramatic phenomena such as whirlpools and eddies.

WAVES A N D T ID E S LAPPING WAVES

Waves lapping on the seashore meet a rocky stream at low tide near Kipahulu on the southeast coast of the Hawaiian island of Maui, in the Pacific.

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WAVES AND TIDES

Ocean Waves

Wave Generation

WAVES ARE DISTURBANCES

in the ocean that transmit energy from one place to another. The most familiar types of waves—the ones that cause boats to bob up and down on the open sea and dissipate as breakers on beaches—are generated by wind on the ocean surface. Other wave types include tsunamis, which are often caused by underwater earthquakes (see p.49), and internal waves, which travel underwater between water masses. Tides (see p.78) are also a type of wave.

Wave Properties

CAPILLARY WAVES (RIPPLES)

A group of waves consists of several crests separated by troughs. The height of the waves is called the amplitude, the distance between successive wave crests is known as the wavelength, and the time between successive wave crests is the period. Waves are classified into types based on their periods. They range from ripples, which have periods of less than 0.5 seconds, up to tsunamis and tides, whose periods are measured in minutes and hours (their wavelengths range from hundreds to thousands of miles). In between these extremes are chop and swell—the most familiar types of surface wave. Ocean waves behave like light rays: they are reflected or refracted by obstacles they encounter, such as islands. When different wave groups meet, they interfere—adding to, or canceling, each other. wavelength still-water level

direction of wave motion

wave height (amplitude)

disordered sea surface in fetch area

wind direction

ripples turn to chop

outside the fetch, waves become sorted by speed and wavelength

CHOPPY SEA

In a choppy sea, the waves are 4–20 in (10–50 cm) high and have a wavelength of 10–40 ft (3–12 m).

Within the wave-generation area, the sea surface is usually quite confused—the result of groups of waves of different size and wavelength interfering with each other. Outside this area, the waves become sorted by speed to produce a more regular pattern, called a swell.

direction of wave advance fetch (area over which wind blows)

FULLY DEVELOPED ROUGH SEA

Wind speeds over 40 mph (60 kph) can generate very rough seas with waves more than 10 ft (3 m) high.

path of individual water particle

PARTICLE MOVEMENT

INTRODUCTION

As waves pass over the surface, the particles of water do not move forward with the waves. Instead, they gyrate in little circles or loops. Underwater, the particles move in ever-smaller loops. At a depth below about half the distance between crests, they are quite still.

These tiny waves are just a few millimetres high and have a wavelength of under 1½ in (4 cm).

BUILDING WAVES

crest

trough

Wind energy is imparted to the sea surface through friction and pressure, causing waves. As the wind gains strength, the surface develops gradually from flat and smooth through growing levels of roughness. First, ripples form, then larger waves, called chop. The waves continue to build, their maximum size depending on three factors: wind speed, wind duration, and the area over which the wind is blowing, called the fetch. When waves are as large as they can get under the current conditions of wind speed and size of fetch, the sea surface is said to be “fully developed.” The overall state of a sea surface can be summarized by the significant wave height—defined as the average height of the highest one-third of the waves. For example, in a fully developed sea produced by winds of about 25 mph (40 kph), the significant wave height is typically about 8 ft (2.5 m).

Wave Propagation ROGUE WAVES

Interference between two or more large waves occasionally causes a giant or “rogue” wave. This one, recorded in the Atlantic Ocean in 1986, had an estimated height of 56 ft (17 m). It broke over the ship pictured, bending its foremast back by 20˚.

In the fetch, many different groups of waves of varying wavelength are generated and interfere. As they disperse away from the fetch, the waves become more regularly sized and spaced. This is because the speed of a wave in open water is closely related to its wavelength. The different groups of waves move at different speeds and so are naturally sorted by wavelength: the largest, fastest-moving waves at the fore, the smaller, slower-moving ones behind. This produces a regular wave pattern, or swell. Occasionally, groups of waves from separate storms interfere to produce unusually large “rogue” waves. As they propagate across the open ocean, wind-generated waves maintain a constant speed, which is unaffected by depth until they reach shallow water. Only with waves of extremely long wavelength—tsunamis—is the speed of propagation affected by water depth. SWELL

A swell is a series of large, evenly spaced waves, often observed hundreds of miles away from the storm that spawned them. Wavelengths range from tens to hundreds of feet.

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PLUNGING BREAKER

“Barrel” or “tube-forming” breakers like this occur when the waves reaching shore have large amounts of energy. The seabed must be firm and quite steep.

direction of wave motion

water motion occurs offshore to depth of half the wavelength

wave shortens in length and decreases in speed but increases in height

wave reaches critical ratio of height to length and begins to break

water motion caused by the wave begins to interact with the sea bed and slow down

SHOALING AND BREAKING

Shoaling occurs as waves enter shallow water. The wave length and speed both decrease, but the wave gains height. When the crest gets too steep, it curls and breaks.

HUMAN IMPACT

RIDING THE WAVES

water carried up shore in swash zone

Arrival on Shore As waves approach a shore, the motion they generate at depth begins to interact with the sea floor. This slows the waves down and causes the crests in a series of waves to bunch up—an effect called shoaling. The period of the waves does not change, but they gain height as the energy each contains is compressed into a shorter horizontal distance, and eventually break. There are two main types of breaker. Spilling breakers occur on flatter shores: their crests break and cascade down the front as they draw near the shore, dissipating energy gradually. In a plunging breaker, which occurs on steeper shores, the crest curls and falls over the front of the advancing wave, and the whole wave then collapses at once. Waves can also refract as they reach a coastline. This concentrates wave energy onto headlands (see p.93) and shapes some types of beach (see p.106). WAVE REFRACTION

When waves enter a bay enclosed by headlands, they are refracted (bent) as different parts of the wave-front encounter shallow water and slow down.

INTRODUCTION

When a swell reaches a suitably shaped beach, it can produce excellent surfing conditions. Small spilling breakers are ideal for novice surfers, while experts seek out large plunging breakers that form a “tube” they can ride along. For tube-riding, the break of the wave must progress smoothly either to the right or left. Here, a surfer rides a rightbreaking wave in Hawaii— it is breaking from left to right behind the surfer.

wave finally breaks

WAVES AND TIDES

Tides

Tidal Patterns

TIDES ARE REGULAR RISES AND FALLS

in sea level, accompanied by horizontal flows of water, that are caused by gravitational interactions between the Moon, Sun, and Earth. They occur all over the world’s oceans but are most noticeable near coasts. The basic daily pattern of high and low tides is caused by the Moon’s influence on the Earth.Variations in the range between high and low tides over a monthly cycle are caused by the combined influence of the Sun and Moon.

High and Low Tides

If no continents existed and the Moon orbited in the Earth’s equatorial plane, the sweeping of the tidal bulges over the oceans would produce two equal daily rises and falls in sea level (a semidiurnal tide) everywhere on Earth. In practice, landmasses interfere with the movement of the tidal bulges, and the Moon’s orbit tilts to the equatorial plane. Consequently, many parts of the world experience tides that differ from the semidiurnal pattern. A few have just one high and one low tide a day (called diurnal tides), and many experience high and low tides of unequal size (known as mixed semidiurnal tides). In addition, the tidal range, or difference in sea level between high and low water, varies considerably across the globe.

0

6

12

18

24

18

24

3m/10ft 2m/6ft 1m/3ft 0m/0ft DIURNAL TIDE 0

6

12

3m/10ft

mixed semidiurnal small tidal range

This map shows the general pattern of tides (diurnal, semidiurnal, or mixed) and size of tidal range (average difference between high and low water) around the world.

1m/3ft 0m/0ft MIXED SEMIDIURNAL TIDE

medium tidal range large tidal range

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OCEAN

SOUTHERN OCEAN

OCEAN

INTRODUCTION

SEMIDIURNAL TIDE

IC

Compared to permanently submerged plants and animals, organisms living in the intertidal zone have to cope with many extra stresses. They need to adapt, for instance, to the problem of becoming dried out (desiccated) when the tide is out. They may also have to endure extreme cold on frosty winter nights and even predation by land animals. Mussels, for example, often have to wait for hours between high tides to feed. At low tide, their shells close tightly to prevent desiccation and to protect against predators.

0m/0ft

T

INTERTIDAL LIFE

1m/3ft

T

bulges due to combined forces

The two ocean bulges caused by the gravitational interaction between the Earth and Moon are shown (much exaggerated) here.

2m/6ft

2m/6ft

diurnal

24

3m/10ft

GLOBAL PATTERNS

KEY

INDIAN

DAILY TIDES

Time (hrs) 12 18

6

A

Although the Moon is usually thought of as orbiting the Earth, in fact both bodies orbit around a common centre of mass – a point located inside the Earth. As the Earth and Moon move around this point, two forces are created at the Earth’s surface: a gravitational pull towards the Moon, and an inertial or centrifugal force directed away from the Moon. These forces combine to produce Earth gravitational pull of Moon creates tidal two bulges in the Earth’s oceans: bulge one towards the Moon, and the other away from it. As the Earth spins on its axis, these bulges sweep Moon over the planet’s surface, producing inertial force creates second high and low tides. The cycle tidal bulge repeats every 24 hours 50 minutes (one lunar day) rather than every 24 hours (one solar day), because centre of mass of during each cycle, the Moon Earth–Moon moves round a little in its orbit. system

Earth’s spin causes bulges to sweep over surface

0

Tide heights

78

TIDES

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Sun SPRING TIDES

new Moon

high tide low tide

low tide

high tide

full Moon

Sun NEAP TIDES

first quarter Moon low tide

high tide

Tidal Currents

In addition to the daily cycle of high and low tides, there is a second, monthly, cycle. In this case, the Sun and Moon combine to drive the cycle. As with the Moon, the interaction between the Earth and Sun causes bulges in the Earth’s oceans, though these are smaller than those caused by the Moon. Twice a month, at the times of new and full Moon, the Sun, Moon, and Earth are aligned, and the two sets of tidal bulges reinforce each other. The result is spring tides – high tides that are exceptionally high, and low tides that are exceptionally low. By contrast, at the times of first and last quarter Moon, the effects of the Sun and Moon partly cancel out, bringing tides with a smaller range, called neaps.

The vertical variation in sea level that occurs locally with tides can happen only through horizontal flows of water, called tidal currents. Over each daily tidal cycle, the currents typically (but not invariably) run fastest about half-way between high and low tide at that location – at intermediate times they slow (“slack water”) and then reverse direction. The shape of a coast can have a crucial influence on current strength. Bottlenecks to water flow, such as narrow channels and promontories, are often associated with very powerful currents, called tidal races, that develop twice or four times a day. Where the flowing water meets underwater obstructions, phenomena such as whirlpools or vortices (spiralling, funnel-shaped disturbances), eddies (larger, flatter, circular currents), and standing waves may develop. Other tide-related phenomena include tide rips – turbulence caused by converging currents – and overfalls, defined as a tidal Wellington current flowing opposite to the wind direction.

high tide

low tide

FIRST QUARTER

ALTERNATING SPRINGS AND NEAPS

last quarter Moon

Twice a month (top), the alignment of the Sun, Moon, and Earth creates spring tides. At other times (left), when the Sun and Moon lie at right angles, it creates neap tides. The alternation between springs and neaps can be seen in the 28-day tidal graph shown below. FULL MOON

LAST QUARTER

TIME OF LOW WATER, WELLINGTON

COOK STRAIT CURRENTS

NEW MOON

TIDE HEIGHT

NEW MOON

Monthly Cycle

SPRING

NEAP

SPRING

NEAP

These maps show the pattern of strong tidal currents in the Cook Strait, between the North and South islands of New Zealand, which occur twice a day, just over six hours apart. Water must funnel through a narrow channel in the Strait.

Wellington

TIME OF HIGH WATER, WELLINGTON

SPRING

Due to tides, large swathes of coast around the world are alternately covered and uncovered by the sea. This intertidal sandflat in Northumberland, England, has a tidal range averaging about 4m (13ft).

INTRODUCTION

LOW TIDE AT BAMBURGH BEACH

80 HUMAN IMPACT

SURVIVING THE OLD SOW

MINI-VORTEX

This mini-whirlpool, about 20 ft (6 m) wide and 16 in (50 cm) deep, would be called a “piglet” by experienced Old Sow watchers. Sometimes, several of these small vortices occur, rather than a single large whirlpool. ATLANTIC OCEAN NORTHWEST

The Old Sow Whirlpool FEATURES

Tidal race, small whirlpools, occasional large whirlpool TIMING

Four times daily LOCATION Off the southern tip of Deer Island, New Brunswick, Canada

Situated at the southern end of Passamaquoddy Bay on the US– Canada border, the Old Sow is one of the largest whirlpools in the world,

ATLANTIC OCEAN NORTHEAST

Lofoten Maelstrom FEATURES

Tidal race and large, weak eddy TIMING

Four times daily LOCATION Between Lofoten Point and Mosken in the Lofoten Islands, off northwest Norway

INTRODUCTION

Also known as the Moskenstraumen, the Lofoten Maelstrom is a complex pattern of sea-surface disturbances caused by tidal flows of water over

TIDAL DISTURBANCE

For centuries, the Lofoten Maelstrom had a reputation as one of the world’s most powerful tidal phenomena.

and by far the largest in the Americas. Passamaquoddy Bay is at the lower end of the Bay of Fundy, which is famous for its strong tides. The Old Sow, when it appears, is located at a spot where various tidal streams flowing through the channels

between different islands converge during the ebb tide or diverge during the flood tide. As they flow, these currents encounter underwater obstructions, such as ledges and small

COASTAL SETTING

The Old Sow develops between Deer Island (top) and Moose Island in Maine, USA (foreground).

a broad, submerged ledge of rock between two of the Lofoten Islands. These flows result from large sea-level differences that develop four times a day between the Norwegian Sea and the Vestfjord on the eastern side of the Lofoten Islands. The word “maelstrom” originates with the tidal phenomena in this area, and is derived from the Nordic word male, meaning “to grind.” In Norse mythology, the Maelstrom was the result of a large salt-grinding millstone on the floor of the Norwegian Sea, which sucked water into its central hole as it turned. First described by the Greek explorer Pytheas in the 3rd century bc,

the Lofoten Maelstrom is marked on many historical charts as an enormous and fearsome whirlpool. In 1997, a detailed study of tidal currents in the vicinity of the island of Mosken found that the reality is somewhat different. Although some strong tidal currents were measured, no obvious large whirlpool, with a vortex, was detected. Instead, the researchers found a weak eddy, about 4 miles (6 km ) in diameter, to the north of Mosken. This eddy develops twice a day during the flood tide, when it moves in a clockwise direction, and twice on the ebb tide, when it moves slightly farther north and goes counterclockwise.

The Old Sow has caused about a dozen fatalities from drowning over the past 200 years. Most of these involved mariners who strayed too close to the whirlpool in small rowboats or sailboats. In recent times, a few people in powerboats have had anxious experiences when their engines have stalled. Experienced mariners advise that if caught in a whirlpool, the priority is to keep the boat on an even keel and avoid getting swamped. Most objects floating in a stable position will eventually spin clear. seamounts, so as they reach their maximum speed of up to 17 mph (28 km/h), the whole sea surface in this area becomes rough and disordered. Typical disturbances include standing waves, troughs (long depressions in the surface), and “boils” (smooth circular areas where water spouts up from deep below). Occasionally and unpredictably, the Old Sow itself appears, forming a vortex that can be 100 ft (30 m) wide and 10 ft (3 m) deep. More often, one or several smaller vortices, known locally as piglets, appear. As with all tidal disturbances, these phenomena are more powerful during a spring tide, which occurs a day or two after a full or new moon.

PEOPLE

JULES VERNE The French novelist Jules Verne (1828-1905) made reference to the Lofoten Maelstrom in his tale of undersea exploration, Twenty Thousand Leagues Under the Sea. At the end of the novel, Captain Nemo and his submarine, Nautilus, are sucked down into the whirlpool, “whose power of attraction extended to a distance of twelve miles,” suffering an unknown fate.

81 ATLANTIC OCEAN NORTHEAST

Saltstraumen FEATURES

Tidal race and small whirlpools TIMING

Four times daily Between Saltenfjord and Skjerstadfjord, northwest coast of Norway

LOCATION

The Saltstraumen tidal race occurs on the northwest coast of Norway and is generally acknowledged to be the strongest and most extreme tidal current in the world. It forms at a bottleneck between the Saltenfjord, an inlet from the Norwegian Sea, and the neighboring Skjerstadfjord: its driving force is a difference in sea level of up to 10 ft (3 m) that develops four times a day between the two bodies of water. The channel at the center of the bottleneck—Saltstraumen itself—is a 2-mile- (3-km-) long strait between two headlands, with a width of just 500 ft (150 m) and a depth that varies from 65 to 330 ft (20 to 100 m). Twice

a day, some 105 billion gallons (400 billion liters) of water roar through this strait on the flood tide, reaching maximum speeds of up to 25 mph (40 km/h), as tidal forces act to fill the 30-mile(50-km-) long Skjerstadfjord. Twice a day, the waters flow out again through the same channel. The flows of water, and associated whirlpools, are equally strong during the ebb as the flood tide. Despite Saltstraumen’s ferocity, the channel is regularly used by shipping. For short periods every day, the tidal flows slow almost to a halt, allowing large vessels to pass safely into and out of Skjerstadfjord. Smaller vessels do remain at risk from residual underwater currents during these periods of “slack water,” but many experienced pilots still venture out. Saltstraumen offers both interesting opportunities for divers and excellent angling (see panel, below). Incoming tides carry large amounts of plankton through the channel, and fish of various sizes follow.

DANGEROUS WATERS

When the tidal race flows, the spinoff vortices, which can be 33 ft (10 m) across, are capable of pulling objects down to the rocky bottom of the channel.

DISCOVERY

LIFE BENEATH THE WHIRLPOOLS It is possible to dive into and explore the Saltstraumen, although this can safely be attempted only when the tidal streams are at a minimum. Divers have discovered rich and colorful marine life at the bottom of the channel, dominated by long strands of kelp and a variety of invertebrates, as well as fish such as lumpsuckers, coley, and wolf-fish. TEEMING WITH LIFE

Invertebrate life at the bottom of the channel includes colorful sponges and anemones.

ATLANTIC OCEAN NORTHEAST

Corryvreckan Whirlpool FEATURES

Tidal race, standing waves, and whirlpools TIMING

Twice daily Between the islands of Jura and Scarba, west coast of Scotland, UK

LOCATION

SPIN-OFF VORTEX

In the whirlpool area, massive upthrusts of water occur in pulses, producing vortices that spin away with the tidal flow.

DISTURBED SEA

An area of disturbance begins to develop in the channel north of Jura, seen here with the island of Scarba lying behind it.

ATLANTIC OCEAN NORTHEAST

Slough-na-more Tidal Race FEATURES

Tidal race with eddies and standing waves TIMING

Four times daily Between Rathlin Island and Ballycastle Bay, County Antrim, Northern Ireland, UK

LOCATION

The Slough-na-more Tidal Race results from strong tidal flows of billions of gallons of seawater between the Atlantic Ocean and the Irish Sea, via a narrow channel. During spring tides, the tidal stream can attain a speed of 8 mph (13 km/h). Where it passes Rathlin Island, a complex of fastmoving currents, eddies, and standing waves is created. In contrast, the same sea area is usually calm during other phases of the tidal cycle. In 1915, the strength of the Slough-na-more Tidal Race forced the Irish steam coaster SS Glentow aground on the Irish coast, and the ship later broke up.

INTRODUCTION

The most famous tidal phenomenon in the British Isles can be found in the Gulf of Corryvreckan. Twice a day on the flood tide, strong Atlantic currents and unusual underwater topography conspire to produce an intense tidal race. As the tide enters the narrow bottleneck at Corryvreckan, currents of up to 14 mph (22 km/h) develop. Underwater, these currents encounter a variety of irregular features on the

seabed, including a conical obstruction known as the Pinnacle, which rises to within 95 ft (30 m) of the surface. The steep east face of this obstruction forces a plume of water to the surface, producing whirlpools and standing waves up to 13 ft (4 m) high, and the roar of the rushing water can be heard up to 3 miles (5 km) away. Over the years, the Corryvreckan has caused numerous emergencies – the author George Orwell nearly drowned there in 1947.

82

TIDES AND WAVES ATLANTIC OCEAN NORTHEAST

Needles Overfalls

ATLANTIC OCEAN EAST

Garofalo Whirlpool

FEATURES

FEATURES

Tidal race and overfalls TIMING

Tidal race, small whirlpools, and overfalls

Four times daily

TIMING

PACIFIC OCEAN NORTHEAST

Yellow Bluff Tide Rip FEATURES

Tide rip, standing waves, and eddies

Four times daily

TIMING

Twice daily LOCATION Needles Channel, northwestern coast of the Isle of Wight, England, UK

Strait of Messina, between the northeast coast of Sicily and Calabria in mainland Italy

LOCATION

LOCATION

The Needles Channel is a 5-mile(7-km-) long stretch of water between a line of chalk sea stacks on one side (the Needles) and an underwater reef on the other. This stretch of water is affected by short, breaking waves (overfalls) at the time of the maximum ebb or flood tide. If the wind is blowing in the opposite direction of the tidal stream, these overfalls are greatly exacerbated, producing an extremely rough sea.

PACIFIC OCEAN NORTHEAST

Skookumchuck Narrows Tidal Race Tidal race, small whirlpools, and standing wave on flood tide

FEATURES

TIMING Four times daily; flood tide twice daily LOCATION

Skookumchuck Narrows, British Columbia,

Canada

San Francisco Bay, California, US

The Strait of Messina separates the “toe” of Italy from the Mediterranean island of Sicily. It varies in width from 2 to 10 miles (3 to 16 km) and is the site of numerous complex currents and small whirlpools that vary over the tidal cycle and hamper navigation through the Strait. In Italy, the small whirlpools that form are called garofali, but in the English-speaking world, the whole system of tidal disturbances is known as the Garofalo Whirlpool.

A tide rip is a stretch of rough, turbulent water caused by a tidal current converging with, or flowing across, another current. Thus it differs from a tidal race, which occurs where a tidal stream of water accelerates through a narrow opening in a coast. An example of a tide rip occurs at a place called Yellow Bluff in San Francisco Bay, not far from the bay’s entrance, the famous Golden Gate.

One of the world’s most famous tidal races occurs at the Skookumchuck Narrows on British Columbia’s Sunshine Coast, not far from Vancouver (Skookum is a native American word for “strong” and chuck means “water”). Four times a day, there is a strong tidal rush of water through this 1,000-ft- (300-m-) wide channel, which connects two inlets into the coast—the Sechelt and Jervis inlets. A 10-ft (3-m) difference in sea level between low and high tide causes some 167 billion gallons (760 billion

liters) of seawater to rush through the gap, creating turbulence and some small whirlpools. On the flood tide, when water is flowing into the Sechelt Inlet (but not the ebb tide, when it flows out), the tidal stream across an outcrop of bedrock in the channel creates a large standing wave—a mound of breaking water that remains stationary at a particular spot on the surface. At its peak, the flow rate is about 4.75 million gallons (18 million liters) per second, and current velocities can reach 20 mph (32 km/h).

Four times a day, strong movements of water occur through the Golden Gate—twice flowing into the bay on the flood tide and twice flowing out on the ebb tide. These currents can reach a speed of up to 5 mph (8 km/h) during spring tides. Inside the bay, the pattern of currents becomes more complex, as they either split (during the flood tide) or converge (during the ebb tide) from different parts of the bay. The currents are also modified by the varying depth of the water around the shoreline, by the shoreline’s shape, and by subsurface obstructions. At Yellow Bluff, disturbances to the sea surface are most noticeable during the ebb tide, when the tidal streams are converging, and are characterized by such phenomena as extremely rough, fast-moving water, standing waves, and eddies. The spot is popular with extreme kayakers, who challenge themselves against the strong currents and surf on the standing waves.

HUMAN IMPACT

SURF-KAYAKING

INTRODUCTION

Skookumchuck Narrows is a popular destination for enthusiasts of extreme surf-kayaking. The standing wave that arises there is up to 8 ft (2.5 m) high and 23 ft (7 m) wide and is regarded as one of the world’s great whitewater kayaking locations. When surf-kayaking, the object is to stay in the wave as long as possible, which requires strength and skill.

POWERFUL RAPIDS

Here, water is flowing right to left, from the Sechelt Inlet into Jervis Inlet. Six hours later, it flows back in the opposite direction.

TIDES AND WAVES

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PACIFIC OCEAN NORTHWEST

Naruto Whirlpool FEATURES

Tidal race and whirlpools TIMING

Four times daily Naruto Strait, between the islands of Shikoku and Awaji, Japan

LOCATION

The Naruto is a spectacular system of whirlpools that develops four times a day in a narrow channel separating the island of Shikoku (one of Japan’s main islands) from Awaji Island, a much smaller island lying off Shikoku’s northeastern coast. The channel, called the Naruto Strait, is one of several that join the Pacific Ocean to the Inland Sea, which is a large body of water lying between Shikoku and Japan’s largest island, Honshu. Four times a day, billions of gallons of water move into and out of the Inland Sea through this channel, generated by tidal variations in sea level between the Inland Sea and the Pacific Ocean of up to 5 ft (1.5 m). The tidal flows can reach speeds of up to 9 mph (15 km/h) during spring tides (that is, twice a month, around the time of a full or new moon). They create vortices up to 65 ft (20 m) in diameter where they encounter a submarine ridge. These vortices are not stationary but tend to move with the current, persisting for 30 seconds or more before disappearing. The whirlpools can be viewed from Awaji Island, from sightseeing boats that regularly negotiate the rapids, or from a 4/5-mile- (1.3-km-) long bridge that spans the Naruto Strait. HUMAN IMPACT

ARTISTIC INSPIRATION The Naruto Whirlpool has existed since ancient times. It is mentioned many times in Japanese poetry and is possibly the only tidal phenomenon to feature in a well-known piece of art, namely Whirlpool and Waves at Naruto, Awa Province, by the 19th-century Japanese artist Utagawa Hiroshige (a fragment is shown below).

A walkway hanging beneath the Onaruto Bridge, which spans the Naruto Straits, provides an excellent view of the whirlpools below.

INTRODUCTION

TROUBLED WATERS

OCEAN ENVIRONMENTS

COASTS INCLUDE SOME of the most

beautiful, but also some of the most rapidly changing, places on Earth. There are a great many forms that they can take—from cliffs composed of anything from limestone to lava, to beaches, spits, and barrier islands, river deltas, estuaries, and tidal flats. Each coast has its own unique history of formation, brought about by processes such as land rise and fall, sea-level change, glacial and volcanic action, and marine erosion and deposition. On and around these coasts, a variety of habitat types— ranging from sandy coastal dunes to salt marshes, coastal lagoons, and, in the tropics, mangrove swamps—are shaped by the interaction of tidal flows, breaking waves, discharge of river sediment, and a variety of biological and human-induced processes.

C OA S TS A N D TH E S E A S H O R E SANDSTONE COAST

This dramatic Australian coastline consists of eroded sandstone strata beautifully shaped and sculpted by an azure sea.

88

COASTS AND THE SEASHORE

Coasts and Sea-level Change A COAST IS A ZONE WHERE THE LAND MEETS THE SEA—it

extends from the shoreline inland to the first significant terrain change. Coastlines constantly alter in response to sea-level change, land-based processes, wave action, and tides. Coasts can be classified into many types, some of which are contrasting—for example, two opposite forms linked to sea-level change are drowned and emergent coasts. The sea-level change itself may either have been global in nature (caused by a change in the volume of ocean water, for example) or only local (stemming from regional uplift or sinking of land).

Global Sea-level Change The most important cause of a global change in sea level is an increase or decrease in the extent of the world’s ice sheets and glaciers. This is related to Earth’s climate. If it cools, more water becomes locked up as ice, so there is less in the oceans. If it heats up (global warming), the ice melts and increases the volume of ocean water. Another cause of global sea-level change, which is also affected by climate, is a rise or fall in ocean temperature. Warming lowers ice reduced ocean sheet the density of water, so if the upper layers of the water continental crust oceanic oceans heat up, they expand and increase the depressed by crust ice total volume of the oceans. Any changes in the rises size of the ocean basins, the ocean’s containers, also impact globally on sea levels. For example, a change in activity at mid-ocean ridges can have such an effect and may be important in driving long-term sea-level change. increased ocean water

continental crust rises due to unloading of ice

GLACIAL CYCLES

OCEAN-BASIN CHANGE

During an ice age (top) the volume of ocean water is low as water is locked up in ice sheets. When the ice melts (bottom), the oceans expand, raising sea levels globally.

A slow, global rise in sea level can occur when new crust is produced at a fastspreading mid-ocean ridge. The relatively hot, buoyant new crust swells, pushing the ocean water upward.

old, dense crust

raised sea level

UPLIFTED TERRACE

This coastal region of New Zealand has experienced a localized sea-level fall in the recent geological past, as the land was significantly raised by an earthquake. What was beach is now flat clifftop.

upper mantle slow-spreading ridge

fast-spreading ridge

continental crust

younger, less dense crust has greater volume

OCEAN ENVIRONMENTS

oceanic crust depressed

SINKING ISLANDS

These two volcanic Pacific islands, Rai’atea (top) and Bora-Bora, are subsiding. Locally, the current global rise in sea level is therefore slightly exacerbated.

Local Sea-level Change

Drowned Coasts

Local sea-level change occurs when a particular area of land rises or falls relative to the general sea level. One of the main causes is tectonic uplifting of land, which occurs in regions where oceanic crust is being forced beneath continental crust (a process often associated with earthquakes). Another cause is glacial rebound, which is a gradual rise of a specific area of land after an ice sheet that once weighed it down has melted. During the last ice age, heavy ice sheets covered much of North America and Scandinavia. Since the ice melted, these regions have risen, and they continue to do so today at rates of up to a few inches a year. In contrast, other coastal areas are slowly sinking. Often, this occurs where a heavy load of coastal sediments is pushing the underlying bedrock down. A slow subsidence is occurring, for example, on the eastern coast of the US. Many volcanic islands also start to subside soon after they form. This is due to the fact that the material from which they are created cools, compacts, and then contracts, while the sea floor under them warps downward.

A drowned (or submergent) coast can be the result of either global or local sea-level rise. There are two types—rias and fjords. In a ria coast, the sea-level rise has drowned a region of coastal river valleys, forming a series of wide estuaries, often separated by long peninsulas. In a fjord coast, the sea-level rise has drowned one or more deep, glacier-carved valleys. Both types are RIA COAST characteristically irregular and indented. Due to The coastline around a significant global rise in sea level over the past Hobart, in Tasmania, Australia, was formed 18,000 years, drowned coasts are common by a rise in sea-level worldwide. Ria coasts are particularly prevalent flooding a series of river in northwestern Europe, the eastern US, and valleys. Here, the Hobart Australasia. Large numbers of fjords are present Bridge spans one such in coastal Norway, Chile, Canada, and New Zealand. drowned valley.

89

Emergent Coasts

Past Change

Emergent coasts occur where land has uplifted faster than the sea has risen since the last ice age. The causes are either activity at the edge of a tectonic plate or glacial rebound. On emergent coasts, areas that were formerly sea floor may become exposed above the shoreline, while former beaches often end up well behind the shoreline, or even on clifftops. Sometimes, staircaselike structures called marine terraces are created by a combination of uplift and waves gradually cutting flat platforms at the bases of cliffs (wave-cut platforms). Emergent coasts are typically rocky, but sometimes they have a smooth shoreline. Examples of these coasts occur on the US Pacific Coast and in Scotland, Scandinavia, New Zealand, and Papua New Guinea.

Scientists study past sea-level changes by examining rocks and fossils near shorelines. They also analyze ocean sediments to calculate past ocean temperatures and climatic properties. Over the past 500 million years, global sea levels have fluctuated by more than 1,000 ft (300 m). About 120,000 years ago, sea level was a few meters higher than it is today, but some 20,000 years ago, it was 400 ft (120 m) below today’s level. Most of the rise since then occurred prior to 6,000 years ago. From some 3,000 years ago to the late 19th century, sea level rose at about 1/254–1/127 in (0.1–0.2 mm) per year. In the late 20th century, this increased to an average of about 1⁄15 in (1.7 mm) per year.

RAISED BEACH

FOSSIL MAMMOTH TOOTH

New York Washington D.C.

NORTH AMERICA

Miami UPLIFTED CLIFFS

These marine cliffs in Crete, Greece (right), have been uplifted by tectonic activity, eroded, and finally tilted from the horizontal, also by tectonic activity.

THEN AND NOW

ATLANTIC OCEAN

The red dotted line on this map shows where the east coast of North America was 15,000 years ago. At that time, mammoths roamed on what is now continental shelf—it is not uncommon for a mammoth tooth (above) to turn up in fishing trawls from these areas.

OCEAN ENVIRONMENTS

In this bay in the Hebridean Islands, Scotland (left), the green areas behind the beach are former beaches that have been raised by glacial rebound since the end of the last ice age.

SURROUNDED BY WATER

The Italian city of Venice currently floods up to 200 times a year and is severely threatened by future sea-level rise, although a project to build a tidal barrier is expected to be completed in 2016.

91

Global Warming and Sea-level Rise EFFECTS OF GLOBAL WARMING

PERUVIAN ANDES Global warming is having a marked impact on the world’s glaciers. The majority have shrunk since 1975, as their ice has melted faster than new ice has formed. These photographs from the same viewpoint show the extent of a glacier in the Cordillera Blanca, Peru, in 1980 (left) and 2002 (right). FUNAFUTI ATOLL This atoll is part of Tuvalu, a group of small, low-lying Pacific islands whose future existence is threatened by sea-level rise.

SUBMERGING ISLANDS

complex and, until satellite-based techniques were introduced in 1992, was somewhat imprecise. During the 1980s, a consensus emerged that sea level had been rising at 1/32 –1/8 in (1–3 mm) per year since 1900, whereas the new satellite techniques indicate a current average rise of 1/8 in (3 mm) per year. Since 1900, there has also been a rise in the temperature of Earth’s atmosphere and oceans (global warming) of about 1.44˚F (0.8˚C). There are two plausible mechanisms by which the temperature rise might be linked to the sea-level rise: first, through melting of glaciers and ice sheets, which increases the amount of water in the oceans; and second, through the expansion of seawater as it warms. Since there are no other convincing explanations of what might be causing the sea-level rise, the view of most scientists is that global warming is the cause. Based on different models of the future course of global warming (which most scientists now believe is linked to human activity), it is possible to make various predictions of how sea level will change in the future. For example, the Intergovernmental Panel on Climate Change predicts that, by the end of the 21st century, there will be a further sea-level rise of 11–381/2 in (0.28–0.98 mm). This rise will displace tens of millions of people living in low-lying coastal areas and have a devastating effect on some small island nations. Continued global warming will eventually melt the Greenland Ice Sheet, raising sea levels by about 23 ft (7 m), flooding most of the world’s coastal cities.

GLACIER RETREAT

The measurement of global sea-level change is

HIGH TIDE Homes on Funafuti Atoll are already flooded by lagoon waters from time to time during exceptionally high tides.

OC EA N

TIC

ATLA N

Gulf of Mexico

Miami

flooded area

61/2 -ft (2-m) rise

Miami

Galveston New Orleans Gulf of Mexico

20-ft (6-m) rise

OC EA N

ATLA NT IC

Jacksonville Georgetown

Miami

ANIMALS IN DANGER

Gulf of Mexico

ATLA NT IC

Jacksonville Georgetown

OC EA N

31/4 -ft (1-m) rise

Galveston New Orleans

CITY UNDER WATER Dhaka, the capital of Bangladesh, and about three-quarters of the country’s land area, is less than 27 ft (8 m) above sea level. Much of the country would be flooded by melting of the Greenland Ice Sheet. A rise of 2 ft (65 cm) would cause loss of 40 percent of productive land in southern Bangladesh. About 20 million people in coastal areas are affected by salinity in drinking water now. STARVED TO DEATH Polar bears are one of the animal species most severely threatened by global warming. The bears use Arctic sea ice as their summer hunting ground, and as the extent of sea ice diminishes, so do their opportunities for hunting and feeding.

OCEAN ENVIRONMENTS

The maps below indicate the areas of the southeastern US that would be threatened by sea-level rises of 31/4 ft (1 m), 61/2 ft (2 m), and 20 ft (6 m). A 31/4-ft (1-m) rise is a little above the upper end of estimates for what can be expected this century. With this rise, parts of Florida and southern Louisiana would be inundated up to 18 miles (30 km) from the present coastline. A rise of 20 ft (6 m) — which would be exceeded if the Greenland Ice Sheet were to melt completely — would submerge a large part of Florida, while Louisiana would be flooded as much as 50 miles (80 km) in from the present Jacksonville coastline. This would appear Georgetown to be highly unlikely in this century but could happen within a few hundred years Galveston New Orleans if global warming continues.

POPULATIONS AT RISK

Sea-level Rise in Southeastern US

92

COASTS AND THE SEASHORE

Coastal Landscapes A GREAT VARIETY OF LANDSCAPES ARE FOUND

along the coastlines of the world’s oceans. Coasts are shaped by processes such as sea-level change and wave erosion, as well as by land-based processes such as weathering, erosion and deposition by rivers, glacier advance and retreat, the flow of lava from volcanoes, and tectonic faulting. Some coastal features are made by living organisms, including the reefs built by corals and the harbors, coastal defenses, and artificial islands built by humans.

FRINGING REEF

This reef-fringed coast, around the south Pacific island of Bora Bora, is a secondary coast, as it has been modified by the activities of living organisms, notably corals.

Classification of Coasts Coasts can be classified as either primary or secondary. Primary coasts have formed as a result of land-based processes, such as the deposition of sediment from rivers (forming deltas), land erosion, volcanic action, or rifting and faulting in Earth’s crust. Coasts formed as a result of recent sea-level change, which include drowned coasts and emergent coasts (see pp.88–89), are also usually considered primary, as are coastlines consisting mainly of wind-deposited sand, glacial till, or the seaward ends of glaciers. Coasts are considered secondary if they have been heavily shaped by marine erosional or depositional processes, or by the activities of organisms, such as corals, mangroves, or, indeed, people. A few coasts—for example, emergent coasts that have undergone significant marine erosion—display both primary and secondary features and so fit into an intermediate category.

VOLCANIC COAST ARTIFICIAL COAST

OCEAN ENVIRONMENTS

Singapore Harbor, in Southeast Asia, is an example of a coast that has been heavily shaped by human activity. Before human intervention, it was a mangrove-lined estuary.

SEA ARCH

This spectacular arch in southern England is known as Durdle Door. A remnant of a once much larger headland, it is a classic feature of a marine-eroded coast.

This land-eroded volcanic cone is in the Galápagos Islands. The entire coastline around these islands was formed by volcanic activity and so is a primary coast.

COASTAL LANDSCAPES

Wave-erosion Coasts

energy concentrated on headland as wave front refracts

beach

Of all the different types of coastal landscape, perhaps the most familiar are wave-eroded cliffed coasts, a type of secondary coast. Wave erosion on these coasts occurs through two main mechanisms. First, waves hurl beach material against the cliffs, which abrades the rock. Second, each wave compresses air within cracks in the rocks, and on reexpansion the air shatters the rock. Where waves encounter headlands, refraction (bending) of the wave fronts tends to focus their erosive energy onto the headlands. At these headlands, distinctive features tend to develop in a classic sequence. First, deep notches and then sea caves form at the bases of cliffs on each side of the headland. Wave action gradually deepens and widens these caves until they cut through the headland to form an arch. part of wave Next, the roof of the arch collapses to leave front opposite an isolated rock pillar called a stack, and headland slows as it encounters finally the stack is eroded down to a stump. shallower water

93

part of wave front opposite beach continues forward

erosion eventually divides headland into stacks

lobe of sediment

CONCENTRATION OF WAVE ENERGY

When a wave front reaches a shore consisting of bays and headlands, it refracts in such a way that wave energy tends to be concentrated onto the headlands.

wave front (extended crest of wave)

UNDERCUT CLIFF

SEA CAVE

SEA STACKS

Wave action has eroded a notch, and an adjoining platform, at the base of this cliff in the Caribbean.

This deep indentation and sea cave have been eroded into cliffs in the Algarve, Portugal.

The Old Harry Rocks are chalk sea stacks at a headland near Swanage in southern England. river current

salt marsh spit

headland

movement of sand along beach backwash

swash

Marine-deposition Coasts Marine depositional coasts are formed from sediment brought to a coast by rivers, eroded from headlands, or moved from offshore by waves. An important mechanism in their formation is longshore drift. When waves strike a shore obliquely, the movement of surf (swash) propels water and sediment up the shore at an angle, but backwash drags them back down at a right angle to the shore. Over time, water and sediment are moved along the shore. Where the water arrives at a lower-energy environment, the sediment settles and builds up to form various depositional features, including spits, baymouth bars, and barrier islands (long, thin islands parallel to the coast).

second most common wind and wave direction

direction of longshore drift

prevailing wind and wave direction

SPIT FORMATION

BAYMOUTH BAR

Where a spit extends most or all of the way across the mouth of a bay or estuary, the result is called a baymouth bar. Here, a bar across the mouth of an estuary in Scotland, and an older spit, have created a sheltered coastal area of sandflats and salt marshes.

CLATSOP SPIT

This aerial view shows the impressive Clatsop Spit, at the mouth of the Columbia River in Oregon. The spit extends for 2½ miles (4 km) across the river mouth and is still growing.

OCEAN ENVIRONMENTS

On this coastline, sand and water is carried past the headland by longshore drift, but the sand settles at the mouth of an estuary where the waves are opposed by the sluggish outflow from a river. There it forms a slowly growing spit—a sandy peninsula with one end attached to the land.

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COASTS AND THE SEASHORE ATLANTIC OCEAN NORTHWEST

Greenland Ice Coast TYPE

Primary coast

Extension of ice-sheet to sea level in outlet glaciers FORMATION

EXTENT About 600 miles (1,000 km) LOCATION

Parts of western and eastern coasts of

Greenland

An ice coast forms where a glacier extends to the sea, so that a wall of ice is in direct contact with the water. This is a common feature around the highly indented margins of Greenland, mainly at the landward end of long fjords. Together, these ice walls form an interrupted ice coast, and they are the source of enormous numbers of icebergs, many of which escape the fjords and eventually reach the Atlantic. The ice coast extends along only a fraction of the total Greenland coastline, which is an astonishing 27,500 miles (44,000 km) long.

ATLANTIC OCEAN NORTHWEST

Acadia Coastline TYPE

Primary coast

Glaciation, then drowning by sea-level rise FORMATION

EXTENT

41 miles (66 km)

Southeast of Bangor, Maine, northeastern US

LOCATION

OCEAN ENVIRONMENTS

ICE COAST NEAR CAPE YORK

STAIRWAY TO THE SEA

The tops of the columns form stepping stones that first lead up from the foot of the cliff to a mound and then progress downward until they dip below the sea.

The coastline of Acadia in Maine is one of the most spectacular in the northeastern US. It now forms the Acadia National Park, most of which

is found within a single large island, Mount Desert Island, and some smaller associated islands. Sea-level rise since the last ice age has separated these islands from each other and from the mainland. The mountains that make up the basis of this coastline began to form 500 million years ago from seafloor sediments. Magma (molten rock) rising up from Earth’s interior intruded into and consumed these sedimentary rocks, producing a mass of granite that was gradually eroded to form a ridge. About 2–3 million years ago, a huge ice sheet started to blanket the area, depressing the land and sculpting out a series of mountains

MOUNT DESERT ISLAND

The south-facing coast of Mount Desert Island consists of a series of fractured granitic steps that were produced by the action of glaciers some 100,000 years ago.

separated by U-shaped valleys. Since the ice sheet receded, the land has gradually rebounded upward, but global sea-level rise has caused the Atlantic to overtake the rebound at a rate of 2 in (5 cm) per century. Today, waves and tidal currents are major agents of change at Acadia, gradually eroding the cliffs and depositing rock particles mixed with shell fragments at coves around the coastline.

COASTAL LANDSCAPES ATLANTIC OCEAN NORTHWEST

HUMAN IMPACT

Hatteras Island TYPE

CAPE HATTERAS LIGHTHOUSE

Secondary coast

FORMATION Deposition of sediment by waves and currents EXTENT

Erosion and deposition often cause shorelines to migrate. In 1999, the Cape Hatteras Lighthouse was moved because the sea had begun to lap at its base, threatening its destruction.

70 miles

(112 km) LOCATION Off the coast of North Carolina, northeastern US

Hatteras Island is a classic barrier island of sandy composition. It runs parallel to the mainland and is long and narrow, with an average width of 1,500 ft (450 m), and has been shaped by complex processes of deposition effected by ocean currents and waves. It is part of a series of barrier islands called the Outer Banks and has two distinct sections, which join at a promontory called Cape Hatteras. The dangerously turbulent waters in this area have resulted in hundreds of shipwrecks over the centuries.

ATLANTIC OCEAN WEST

Les Pitons TYPE

Primary coast

Volcanic lava-dome formation followed by volcano collapse and erosion

FORMATION

EXTENT

41/2 miles (7 km)

Southwestern coast of St. Lucia, Lesser Antilles, eastern Caribbean

LOCATION

The southwestern coastline on the Caribbean island of St. Lucia is rocky, highly indented, and steeply shelving. A landmark here is Les Pitons (“The Peaks”), two steep-sided mountain spires, each more than 2,430 ft (740 m)

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HATTERAS SHORELINE

Hatteras Island is a typical barrier island, being low-lying with wave-straightened shorelines.

NEW POSITION

The lighthouse is now located about 1,500 ft (450 m) back from the shoreline.

high. These are the eroded remnants of two lava domes (large masses of lava) that formed some 250,000 years ago on the flank of a huge volcano. The volcano later collapsed, leaving behind the peaks and other volcanic features in the area. The volcanic rocks on this coast are densely vegetated, except on the very steepest parts of Les Pitons themselves. Beneath the sea are some scattered coral reefs within a series of protected marine reserves. This region was declared a World Heritage Site in 2004. TWIN PEAKS

In this view, Petit Piton is the nearer peak, while Gros Piton, which is slightly higher and much broader, is visible in the background.

ATLANTIC OCEAN NORTHEAST

Giant’s Causeway TYPE

Primary coast

Cooling of basaltic lava flow from an ancient volcanic eruption FORMATION

EXTENT 3/5

mile (1 km)

Northernmost point of County Antrim, Northern Ireland, UK

LOCATION

OCEAN ENVIRONMENTS

The Giant’s Causeway is a tightly packed cluster of some 40,000 columns of basalt (a black volcanic rock). It is located at the foot of a sea cliff that rises 300 ft (90 m) on the northern coast of Northern Ireland. Although legend says the formation was created by a giant named Finn McCool, it in fact resulted from a volcanic eruption some 60 million years ago, one of a series that brought about the opening up of the North Atlantic. The eruption spewed up vast amounts of liquid basalt lava, which cooled to form the columns. They are up to 42 ft (13 m) tall and are mainly hexagonal, although some have four, five, seven, or eight sides.

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COASTS AND THE SEASHORE ATLANTIC OCEAN NORTHEAST

Gruinard Bay TYPE

Primary coast

Ice-sheet retreat and postglacial rebound FORMATION

EXTENT

8 miles (13 km)

LOCATION West of Ullapool, northwestern Scotland, UK

Around Gruinard Bay in Scotland there is evidence of a phenomenon known as postglacial rebound, in which a landmass, once pushed down

ATLANTIC OCEAN NORTHEAST

White Cliffs of Dover TYPE

Secondary coast

FORMATION Marine erosion of a large mass of ancient chalk EXTENT

11 miles (17 km)

LOCATION Southeastern coast of England, to east and west of Dover, UK

One of England’s most famous natural landmarks, the White Cliffs of Dover run along the northwestern side of the Strait of Dover, the narrowest part of the English Channel. They are complemented on the French side of the Strait by similar cliffs at Cap Blanc

by the huge weight of ice sheets during the last glacial period, rises again. In some areas, such as Scotland and Scandinavia, this upward rebound has outstripped the sea-level rise caused by the ice sheets melting. At Gruinard Bay, rebound is indicated by its raised beaches—flat, grassy areas behind the present-day beaches. Over the last 11,000 years, this part of Scotland has been moving upward relative to sea level, up to 4 in (10 cm) per century. RAISED BEACH

The green area beyond the present-day beach, well above the line of high tide, is the remnant of an ancient beach.

Nez. The chalk from which the cliffs are composed was formed between 100 million and 70 million years ago, when a large part of what is now northwestern Europe was underwater. The shells of tiny planktonic organisms that inhabited those seas gradually accumulated on the sea floor and became compressed into a layer of chalk that was several hundred yards thick. Subsequently, as the sea level fell during successive ice ages, this mass of chalk lay above the sea, and it later formed a land bridge between present-day England and France. However, about 8,500 years ago, the buildup of a large lake in an area now occupied by the southern North Sea caused a breach

ATLANTIC OCEAN NORTHEAST

Devon Ria Coast TYPE

Primary coast

Former river valleys drowned by sea-level rise FORMATION

EXTENT

About 60 miles

(100 km) Between Plymouth and Torbay, southwestern coast of England, UK

LOCATION

Much of the south coast of the English county of Devon consists of the drowned valleys of the Dart, Avon,Yealm, and Erme rivers, and the Salcombe–Kingsbridge Estuary. The inlets, also known as rias, are separated by rugged cliffs and headlands. This beautiful coastal area was formed by the partial flooding of valleys, through which small rivers once flowed, as a result of global sea-level rise since the last ice age. The rise in sea level has been accentuated by the fact that the southern parts of the British Isles have been tipping downwards since the last glacial maximum at a rate of up to 3 in (7 cm) per century. in the land-bridge. It eroded rapidly, causing flooding of the area that now forms the English Channel. Today, the cliffs at Dover continue to be eroded at an average rate of an inch or two per year. Occasionally a large chunk detaches from the cliff edge and falls to the ground. Many marine fossils have been discovered in the cliffs, ranging from sharks’ teeth to sponges and corals.

SALCOMBE–KINGSBRIDGE ESTUARY

The highly scenic Salcombe Estuary is the largest of the five rias on the south Devon coast. Its protected waters provide ideal conditions for sailing.

ATLANTIC OCEAN NORTHEAST

Cape Creus TYPE

Primary coast

Land-eroded rocky coastline of schists and other metamorphic and igneous rocks

FORMATION

EXTENT

6 miles (10 km)

Northeast of Girona, northeastern Catalonia, Spain

LOCATION

HIGH CHALK CLIFFS

Up to 330 ft (100 m) high, these cliffs owe their remarkable appearance to the almost pure chalk of which they are composed.

OCEAN ENVIRONMENTS

AN EASTERLY POINT OF THE CAPE

Cape Creus marks the point where the mountains of the Pyrenees meet the Mediterranean Sea. It has one of the most rugged coastlines in the entire Mediterranean region, with cliffs made of extremely roughtextured rocks, interspersed by small coves. Designated as a natural park in 1998, Cape Creus also boasts a varied underwater marine life, and is rich in invertebrate animals such as sponges, anemones, fan worms, and red corals. As such, it is a popular diving location. The landscape is said to have inspired the Spanish surrealist artist Salvador Dali (1904–1989), and it features in many of his paintings, including The Persistence of Memory.

COASTAL LANDSCAPES

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ATLANTIC OCEAN NORTHEAST

Western Algarve TYPE

Secondary coast

Erosional action of waves on ancient rock strata FORMATION

84 miles

EXTENT

(135 km) Southern and southwestern coast of Portugal

LOCATION

BALANCED STACK

At Marinha Beach near Carvoeiro, wind and waves have produced distinctive rock formations, such as this eroded sea stack balanced on the shoreline.

ATLANTIC OCEAN EAST

ATLANTIC OCEAN EAST

Nile Delta

Amalfi Coast TYPE

The western Algarve coast extends from the city of Faro in southern Portugal to Cape St.Vincent, at the southwestern tip of the Iberian Peninsula, and then for a further 30 miles (50 km) to the north. This coastline, which is bathed by the warm Gulf Stream, is notable for its picturesque, honey-colored limestone cliffs, small bays and coves, sheltered beaches of fine sand, and emeraldgreen water. Many stretches of this coast show typical features of marine erosion at work, including caves at the feet of cliffs, grottoes, blowholes, arches forming through headlands, and sea stacks (isolated pillars of rock set off from headlands). Although limestone is a primary component of the landscape, other rocks, including sandstones and shales, form parts of the cliffs along scattered stretches of the coast. The strikingly beautiful scenery has made this coast a popular vacation destination.

Secondary coast

TYPE

EXTENT

FORMATION

EXTENT

Southern side of the Sorrento Peninsula, south of Naples, southern Italy

LOCATION

North of Cairo, northern Egypt

The Nile Delta is one of the world’s largest river deltas. As with all deltas, its shoreline is classed as a primary coast because it formed as a result of sediment deposition from a river, a land-based process. The flow of water that formed it and nourishes it has been reduced significantly by the Aswan Dam in Upper Egypt and by local water usage. The sand belt at the delta’s seaward side, which prevents flooding, is currently eroding, and anticipated future rises in sea level pose a severe threat to its agriculture, freshwater lagoons, wildlife, and reserves of fresh water.

PROTECTIVE BELT

CLIFFS AT SANT ELIA POSITANO

In this satellite view, the sand belt at the front of the Nile Delta is clearly visible. The protrusions through the sand belt mark the mouths of two Nile tributaries.

OCEAN ENVIRONMENTS

Stretching along the southern edge of the Sorrento Peninsula, south of Naples, the Amalfi Coast is famous for its steep cliffs punctuated by caves and grottoes, and for its picturesque coastal towns, some of which are built into the cliffs. The inclined layers of limestone rock that form the cliffs lie at the foot of the Lattari Mountains and were formed between 100 and 70 million years ago.

150 miles

(240 km)

43 miles (69 km)

LOCATION

Primary coast

Deposition of sediment at mouth of Nile River

Marine erosion of folded and inclined limestone rock strata

FORMATION

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COASTS AND THE SEASHORE ATLANTIC OCEAN SOUTHEAST

Skeleton Coast TYPE

Secondary coast

FORMATION

Wind-formed desert dunes EXTENT 500km (310 miles) LOCATION Extending northwest from the city of Swakopmund on the coast of Namibia

The Skeleton Coast is an arid coastal wilderness in southwestern Africa, where the northern part of the Namib Desert meets the South Atlantic. Some stretches of this coast are dominated by sand dunes that extend to the sea; others consist of low gravel plains. An important influence on this largely straight coastline is the Benguela Current, a surface current that flows in a northerly direction offshore, bringing cool waters from the

direction of Antarctica. Prevailing southwesterly winds blow onto the coast from the Atlantic, but as they cross the cold offshore water, any moisture in the air condenses. This leads to an almost permanent fog bank and allows strange desert plants such as Welwitschia mirabilis, a species that survives for hundreds of years, to thrive. The coast is home to a large seal colony at Cape Fria in the north and includes many salt pans.

HUMAN IMPACT

SHIPWRECKS The Skeleton Coast is aptly named. Its frequent fogs, onshore winds, and pounding surf have made it a graveyard for both ships and sailors. Behind the coast is a steep mountain escarpment, so before the days of rescue parties, the escape route for shipwrecked mariners was a long march along the coast through an arid desert. WOODEN SKELETON

This wreck of a wooden vessel is one of many ships that have foundered on this treacherous coast.

HIGH DUNES AND POUNDING SURF

The coast’s high dunes present everchanging contours as they are blown by strong southwesterly winds. Below the dunes, waves pound the beaches.

INDIAN OCEAN NORTHWEST

OCEAN ENVIRONMENTS

Red Sea Coast TYPE

Primary coast

Faulting and sinking of land FORMATION

EXTENT 1,900km (1,200 miles) LOCATION Coasts of Egypt, Sudan, Eritrea, and Saudi Arabia, from gulfs of Suez and Aqaba to Djibouti

The Red Sea was created as a result of a rifting process that has been gradually separating Africa from the Arabian Peninsula for the past 25 million years. Rifting is the splitting of a region of Earth’s crust into two parts, which then move apart, creating a new tectonic plate boundary. This process begins when an upward flow

of heat from the Earth’s interior stretches the continental crust, causing it to thin, and eventually it may fracture, or fault. Sections of crust may sink, and if either end of the rift connects to the sea, flooding will occur, creating new coasts. On both sides of the Red Sea, there is evidence of the downward movement of blocks of crust, in the form of steep escarpments (lines of mountains). The Red Sea shoreline itself shelves steeply in many parts. On the land side, the coast is sparsely vegetated because of the region’s hot, dry climate, but underwater there are many rich and spectacular coral reefs. SEA MEETS DESERT

The steep Sarawat mountain escarpment that runs the length of the coast can be seen in the distance in this view of the Red Sea coast of the Sinai Peninsula.

COASTAL LANDSCAPES INDIAN OCEAN NORTHWEST

Tigris Euphrates Delta TYPE

INDIAN OCEAN NORTHEAST

SATELLITE VIEW

The delta’s seaward edge has advanced by about 250km (150 miles) in the past 3,000 years.

Krabi Coast TYPE

Primary coast

Chemical erosion of limestone followed by drowning FORMATION

Primary coast

Sediment deposition from Tigris, Euphrates, and Karun

FORMATION

EXTENT 160km (100 miles)

150 km (95 miles)

EXTENT

LOCATION

Andaman Sea coast of southwestern

Thailand

Parts of southeastern Iraq, northeastern Kuwait, and southwestern Iran

LOCATION

The area around Krabi on the western coast of southern Thailand is notable for its fantastic-looking formations of partially dissolved limestone, known as karst. This limestone was originally formed about 260 million years ago. At that time, a shallow sea covered what is now south Asia and slowly built up deposits of shells and coral that sediments washed in from the land subsequently buried. These formed layers of limestone, which

The Tigris Euphrates delta is a broad area of marshes and alluvial plain at the northern head of the Arabian Gulf, formed from sediment deposited by three major rivers. An important wildlife haven, the delta suffered great ecological damage between the 1970s and 2003 from various drainage and damming schemes carried out for military and political purposes. Fisheries and several animal species became threatened. Some recovery from the damage has occurred since 2003.

INDIAN OCEAN SOUTHEAST

The Twelve Apostles TYPE

Secondary coast

Wave erosion of cliffs producing large sea stacks FORMATION

EXTENT

3km (2 miles)

Near Port Campbell, southwest of Melbourne, Victoria, southeastern Australia

LOCATION

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were later thrust upwards and tipped over at an angle when India began to collide with mainland Asia some 50 million years ago. Around Krabi and Phang Nga Bay to its north, chemical erosion of these limestone strata by rainwater, followed by sea-level rise, has created thousands of craggy karst hills and islands. These include a number of isolated cone- and cylinder-shaped karst towers that rise out of the sea to heights of up to 210m (700ft) and groups of towers that sit on broad masses of limestone. Many of these karst formations are elongated in a northeast-southwest direction, reflecting the axis (or strike line) around which the original layers of limestone were tipped. KOH TAPU ISLAND

Some of the karst formations along this coast have been weathered into unusual shapes, as in these examples at Koh Tapu Island in Phang Nga Bay to the north of Krabi.

One of Australia’s best-known geological landmarks is a group of large sea stacks formed through the erosion of 20-million-year-old limestone cliffs. Known as the Twelve Apostles, even though there were originally only nine of them, the stacks are up to 70m (230ft) tall. In 2005, one of the stacks collapsed, leaving just eight. Collapses such as this are quite common and are an integral part of the erosion process.

ONGOING EROSION

The effects of wave erosion can clearly be seen at the bases of the remaining Apostles.

VICTORIA HARBOUR

This view shows Victoria Harbour with Hong Kong Island on the left and Kowloon on the right. Visited by more than 200,000 ships per year, the harbour is one of the world’s busiest.

PACIFIC OCEAN WEST

Hong Kong Harbour TYPE

Secondary coast

Artificial coast built around various natural harbours and nearby islands FORMATION

40km (25 miles)

from a satellite island, Ap Lei Chau. The margins of all these harbour areas have been artificially modified by the construction of concrete piers, seawalls, jetties, and other structures. This coastline can be classified as a secondary coast because it has been modified by living organisms, in this case, humans. In the whole of the Hong Kong region, more than 100km (60 miles) of coastline have been artificially constructed or modified.

OCEAN ENVIRONMENTS

EXTENT

Southeast of Guangzhou, on the South China Sea coast of southeastern China

LOCATION

A number of natural harbours surround Hong Kong Island, which is the best-known part of the Hong Kong region of China. The largest, naturally deepest, and most sheltered of these harbours is Victoria Harbour, which has an area of over 42 square km (16 square miles) and is situated between Hong Kong Island and Kowloon Peninsula. Other smaller harbours include Aberdeen Harbour, which separates Hong Kong Island

THE SKELETON COAST

On Africa’s desolate Skeleton Coast, the huge, steep-faced dunes of the Namib Desert meet the cold waters of the southern Atlantic. On this part of the coast, the remains of an ancient shipwreck can be seen close to the shoreline. Above it, fog hangs in the air from condensation of moisture blown in by southwesterly winds.

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COASTS AND THE SEASHORE PACIFIC OCEAN WEST

Ha Long Bay TYPE

Primary coast

Chemical dissolution and drowning of limestone formations FORMATION

EXTENT

75 miles

(120 km) LOCATION On the Gulf of Tonkin, east of Hanoi, Northeastern Vietnam

PACIFIC OCEAN WEST

PACIFIC OCEAN NORTHEAST

Huon Peninsula TYPE

Ha Long Bay is a distinctive region on the coast of Vietnam, within the Gulf of Tonkin. It consists of a body of water filled with nearly 2,000 islands composed of karst (limestone partially dissolved by rainwater). This landscape, which covers an area of just over 585 square miles (1,500 square km), was created by sea-level rise and flooding of a region with a high concentration of karst towers. Several of the islands are hollow and contain

Puget Sound

Primary coast

TYPE

Uplift of fossil coral reefs as a result of tectonic plate movement FORMATION

OCEAN ENVIRONMENTS

EXTENT

Primary coast

FORMATION

Glacier-carved coastal channels and bays EXTENT

90 miles

(150 km)

50 miles (80 km)

LOCATION Eastern Papua New Guinea, north of Port Moresby

LOCATION

For hundreds of thousands of years, the Huon Peninsula has been forced upward at a rate of about 10 in (25 cm) per century by movements of Earth’s crust at a tectonic plate boundary. This activity has pushed coastal coral reefs above the shoreline to form a series of terraced reefs on land. The oldest of these are hundreds of yards back from the coast. By studying them, scientists have learned much about changes in sea level and climate over the past 250,000 years.

Puget Sound, with its numerous channels and branches, was created primarily by glaciers. About 20,000 years ago, a glacier from present-day

AERIAL VIEW OF THE PENINSULA

North and south of Seattle, Washington State, northwestern US

huge caves, and a few have been given distinctive names, such as Ga Choi (“Fighting Cocks”) Island, Man’s Head Island, and the Incense Burner, as a result of their unusual shapes. Most are uninhabited. The Bay’s shallow waters are biologically highly productive and sustain hundreds of species of fish, mollusks, crustaceans, and other invertebrates, including corals. Designated a World Heritage Site in 1998, Ha Long Bay is currently

Canada advanced over the area, covering it in thick ice. Over the next 7,000 years, glaciers advanced and retreated several times. When they finally withdrew, they left behind many deeply gouged channels and thick layers of mud, sand, and gravel deposited by meltwater. Waves and weather have since reworked the deposits, molding landforms and shoreline, and forming beaches, bluffs, spits, and other sedimentary features. SOUND SETTLEMENTS

Much of the shoreline around Puget Sound has now been settled. The town of Tacoma is seen here, with Mount Rainier in the distance.

under threat from destruction of mangroves and from pollution caused by urban development and mining activities nearby. A further problem is a high level of plastic debris jettisoned from tourist boats into the bay. TOWERING LIMESTONE

Several large karst islands, each topped with thick tropical vegetation, tower over a central area of Ha Long Bay. These islands rise up to 660 ft (200 m) above sea level.

PEOPLE

GEORGE VANCOUVER In 1792, the British sea captain George Vancouver (1757–98) became the first European to explore the area we now know as Puget Sound, as commander of the ship Discovery. He gave names to some 75 islands, mountains, and waterways in the area, and the city of Vancouver, Washington, was subsequently named after him. Vancouver named Puget Sound after a Lieutenant Puget, who took the first party ashore to explore its southern end.

COASTAL LANDSCAPES PACIFIC OCEAN NORTHEAST

Big Sur TYPE

Intermediate coast

Tectonic uplift combined with rapid wave erosion

FORMATION

EXTENT

90 miles

(145 km) Southeast of San Francisco, coast of California, US

LOCATION

The Big Sur coastline of central California, where the rugged Santa Lucia Mountains descend steeply into the Pacific Ocean, is one of the most spectacular in the US. Like much of the west coast of North America, Big Sur is an emergent shoreline, in that the coast has risen up faster than sea level

PACIFIC OCEAN SOUTHEAST

Chilean Fjordlands TYPE

Primary coast

Deep glacier-carved valleys flooded by sea-level rise FORMATION

950 miles (1,500 km)

EXTENT

LOCATION Pacific coast of southern Chile from Puerto Montt to Punta Arenas

since the end of the last ice age. This uplift has resulted from interactions at the nearby boundary between the Pacific and North American tectonic plates—this region is crisscrossed by a complex system of faults in Earth’s crust and is subjected to frequent earthquakes. At Big Sur a combination of tectonic uplift and relentless wave erosion has produced steep cliffs and partially formed marine terraces (platforms cut at the base of cliffs by waves and then lifted up). The coast is susceptible to landslides as a result of wave action, the weakening of the cliffs by faulting and fracturing, the destruction of vegetation by summer fires, and heavy winter rainfall.

PACIFIC OCEAN CENTRAL

Hawaiian Lava Coast TYPE

Primary coast

Lava flow into the sea from an active volcano FORMATION

EXTENT

14 miles (20 km)

Southeastern coast of the Big Island of Hawaii, US

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from satellite craters of the active volcano Kilauea. Lava from the Pu’u O’o crater flows some 9 miles (15 km) to the sea, where it cools and hardens to form land. This coastal landscape is a primitive scene of black beaches and dark cliffs made of rough, fractured lava. Plants begin to colonize newly formed areas of the coast within months of their formation.

LOCATION

One of the fastest ways for a coast to change shape is as a result of lava flow to the sea. On southeastern Big Island, new coast has been added intermittently since 1969 as a result of lava flows

STEAM PLUMES

As red-hot lava enters the sea, it solidifies amid huge plumes of steam. Newly forming shoreline sometimes collapses to reveal ripped-open lava tubes.

RAISED PLATFORM

In this view of part of Big Sur, a grassed-over marine terrace (the green area) is visible above the present-day cliff, with a raised ancient cliff behind it.

The Chilean fjordlands are a labyrinth of fjords, islands, inlets, straits, and twisting peninsulas, lying to the west of the snow-capped peaks of the southern Andes. The fjordlands extend for most of the length of southern Chile, as far south as Tierra del Fuego, and their total area is some 21,500 square miles (55,000 square km). Some 10,000 years ago, this region was covered in glaciers, but these have largely retreated into large ice-filled

areas within the mountains on the Chile–Argentina border called the Northern and Southern Patagonian Ice Fields. The glaciers left behind a network of long, deeply gouged valleys, which were filled by glacier meltwater and then flooded by the sea to form today’s fjords. Rainfall here is heavy, and clear skies are rare because the moisture-laden Pacific air cools and forms clouds as

it rises to cross the Andes. On the edges of the fjords, waterfalls cascade down steep granite walls, while hundreds of species of birds nest and feed around the often mist-shrouded coast and islands. Mammals that live along this coast include sea lions, elephant seals, and marine otters.

ICE-CHOKED FJORD

The calving ends of outlet glaciers, which choke the waters with icebergs, are found at the landward end of some fjords.

OCEAN ENVIRONMENTS

BATTERED BY THE SEA

The Eastern Scheldt storm-surge barrier in the Netherlands is one of the world’s largest sea defenses. Its 62 sliding steel gates are held between concrete piers.

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Coastal Defenses TYPES OF DEFENSES

Coastal defense refers to various types of engineering

In 2000, the US Federal Emergency Management Agency estimated that as many as 87,000 houses in the US are in danger of falling into the sea by the year 2060. Among them are the condemned houses, pictured below, on eroding cliffs at Governors Run in Chesapeake Bay, Maryland. In California, about 86 percent of the coast is actively eroding. Similarly, stretches of the eastern coast of England are eroding at a rate of up to 6 ft (1.8 m) a year—the highest rate in Europe. Coastal defenses can slow coastal erosion temporarily, but in the long run maintenance will become prohibitively expensive. In the end, the sea will triumph.

HARD ENGINEERING

ROCK GROYNE This consists of a pile of large rocks built out from the shore. The aim is to slow erosion by causing a local buildup of sand, but it can aggravate erosion nearby.

SOFT ENGINEERING

DUNE STABILIZATION Coastal dunes provide valuable protection against erosion if they can be stabilized and prevented from shifting. This is usually achieved by planting with grasses.

MODERN SOLUTION

Crumbling Coasts

SEA WALL A sea wall is designed to reflect wave energy. Modern walls have a curved top that prevents water from spraying over the wall in storms. A wall protects the land behind it for some years but usually increases erosion of the beach in front of it.

BEACH NOURISHMENT This involves adding large amounts of sand to a beach. Waves and tides spread the material along the coast, temporarily building up its natural defenses.

GEOTUBE A geotube is a long, cylindrical container, over 8 ft (2.3 m) in diameter, made of a durable textile or plastic and filled with a slurry of sand and water. Different types can be laid along the top of a beach, or inside a dune, or just offshore, where they reduce coastal erosion and protect beachfronts. This tube is part of the Barren Island Tidal Wetland project in Maryland.

OCEAN ENVIRONMENTS

DAMS AND STORM-SURGE BARRIERS The Netherlands has invested in an extensive series of engineering works to protect a large region of the country from future marine flooding. Known as the Deltaworks, it includes many dams and movable stormsurge barriers. The works were initiated in 1953 after a serious storm and floods killed a total of 1,835 people.

LARGE-SCALE PROTECTION

techniques aimed at protecting coasts from the sea. The threats posed by the sea fall into two main categories. First is the danger of flooding of low-lying coastal areas during severe storms. Second is the continuous gradual erosion of some coasts. There are a number of different approaches to coastal defense. To prevent flooding of low-lying regions, one solution is to build a large-scale system of dams and tidal barriers. Another is to encourage the development of natural barriers, such as salt marshes, around coasts, and to conserve existing areas of this type. A third possibility is managed retreat. Instead of trying to hold back the sea, some areas of coast are allowed to flood. The idea is that, in time, the flooded land will turn into a marsh, providing natural protection. To slow coastal erosion, various “hard” engineering techniques are commonly employed, such as the building of sea walls, breakwaters, or groynes. These methods can be effective for a while (they usually have to be rebuilt after a few decades), but are expensive and can increase erosion on neighboring areas of coast by interfering with longshore movement of sediment. “Soft” engineering techniques are more environmentally friendly. They include the temporary solution of beach nourishment (see panel, right), which has to be repeated every few years, and encouraging the development of coastal dunes.

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COASTS AND THE SEASHORE

Beaches and Dunes BEACHES ARE DEPOSITS OF SEDIMENTARY MATERIAL, ranging

in size from fine sand to rocks, that commonly occur on coasts above the low-tide line. Sources of beach material include sediment brought to a coast by rivers, or eroded from cliffs or the sea floor, or biological material such as shells. This material is continually moved on and off shore and around coasts, by waves and tides. Wind can also influence beach development and is instrumental in forming coastal dunes.

DISSIPATIVE BEACH AND DUNE

Dissipative beaches are usually made up of fine sand, and they slope at an angle of less than 5˚.

Beach Anatomy

Types of Beaches

A typical beach has several zones. The foreshore is the area between the average high- and low-tide lines. On the seaward side of the foreshore is the nearshore, while behind it is the backshore; the latter is submerged only during the very highest tides and usually includes a flat-topped accumulation of beach material called a berm. The sloping area seaward of the berm, making up most of the foreshore, is the beach face. At the top end of the beach face there are sometimes a series of crescentshaped troughs, called beach cusps. The swash zone is the part of the beach face that is alternately covered and uncovered with water as each wave arrives. Seaward of the swash zone, extending out to where the waves break, is the surf zone. The shape of a beach often alters as wave energy changes over the year.

The level of wave energy, the direction the waves arrive from, and the geological makeup of a coast all affect the type of beach that will form. Dissipative beaches are gently sloping and absorb wave energy over a broad area, while reflective beaches are steeper and shorter, and consist of coarser sediment. If a cliffed coast contains a mixture of both easily eroded and erosion-resistant rock, headlands tend to form, with crescent-shaped beaches within the bays (embayed beaches) or smaller “pocket” beaches. Both of these tend to be “swash-aligned”—the waves arrive parallel to shore and do not transport sediment along the beach. Many long, straight beaches are “driftaligned”—the waves nd arrive at an angle and inla direction of ma longshore drift sediment is moved sand along the beach by embayed beach spit longshore drift. long driftaligned beach

SWASH

The surge of water and sediment up a beach when a wave arrives is called swash. If waves reach a beach at an angle, the combined effect of swash and backwash moves material along the beach. NEARSHORE

swash-aligned beach

RANGE OF BEACHES

This imaginary coast (right) shows several beach types, ranging from a tombolo (a sand deposit between the mainland and an island) to a drift-aligned beach.

FORESHORE

pocket beach tombolo

predominant direction of wind and waves

BEACH PARTS AND ZONES

BACKSHORE

OCEAN ENVIRONMENTS

This photograph (left) shows the main zones on a beach and the locations of the berm, beach face, and beach cusps. It was taken when the sea was approaching low tide.

average low-tide line

average high-tide line surf zone

swash zone

beach face

beach cusp

berm

foredune

berm crest

107

pebbles or medium gravel 3/8 – 1/2 in (8 mm–1.5 cm) in diameter

very fine gravel 1/16 – 1/8 in (2–4 mm) in diameter

very coarse sand 1/32 – 1/16 in (1–2 mm) in diameter

Beach Composition

PEBBLES AND SHELLS

The composition of a beach at any particular location depends on the material available and on the energy of the arriving waves. Most beaches are composed of sand, gravel, or pebbles produced from rock erosion. Sand consists of grains of quartz and other minerals, such as feldspar and olivine, typically derived from igneous rocks such as granite and basalt. Other common beach-forming materials, seen particularly in the tropics, include the fragmented shells and skeletons of marine organisms. In general, higher wave energies are associated with coarser beach material, such as gravel or pebbles, rather than fine sand. Occasionally, large boulders are found on beaches—usually they have rolled down to the shore from local cliffs, but some boulders have ended up on beaches as a result of glacial transport or even backwash from tsunamis.

This high-energy beach (left) contains many large pebbles. Mollusk shells in the beach below reflect favorable offshore feeding conditions for the live mollusks.

Coastal Dunes

medium sand 1/100 – 1/50 in (0.25–0.5 mm) in diameter

fine sand 1/200 – 1/100 in (0.125–0.25 mm) in diameter coarse silt 1/850 – 1/400 in (0.03–0.06 mm) in diameter

GRAIN SIZES

The silts, sands, and gravels that make up most beaches tend to become sorted by the action of waves, with material of different sizes deposited on different parts of the beach.

MARRAM GRASS

This grass is a common colonizer of embryo dunes. It develops deep roots that allow it to tap into deep groundwater stores. The roots bind the sand together, while the grass traps more blown sand, assisting in foredune development.

Coastal dunes are formed by wind blowing sand off the dry parts of a beach. Dunes develop in the area behind the backshore, which together with the upper beach face supplies the sand. For dunes to develop, this sand has to be continually replaced on the beach by wave action. The actual movement of sand to form dunes occurs through a jumping and bouncing motion along the ground called saltation. Some coastal areas have more than one set of vegetated dunes that run parallel to the shoreline. The dunes closest to shore are called foredunes; behind them is a primary dune ridge, secondary dune ridge, and so on. These anchored, vegetated dunes are important for the protection they provide against coastal erosion. On some coasts, non-vegetated, mobile dunes occur; these move in response to the prevailing winds. They can often be anchored by planting with grasses.

This beach in the Seychelles is an example of a reflective beach because of its quite steeply shelving face. It has a distinct berm and berm crest.

OCEAN ENVIRONMENTS

REFLECTIVE BEACH

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COASTS AND THE SEASHORE ATLANTIC OCEAN WEST

ATLANTIC OCEAN SOUTHWEST

Pink Sands Beach

Copacabana Beach

Dissipative beach, protected by reefs

TYPE Embayed, dissipative beach

COMPOSITION Sand mixed with broken shells and skeletons

sand

TYPE

LENGTH

COMPOSITION

LENGTH

White

21/2 miles (4 km)

2.5 miles (4 km)

LOCATION Harbour Island, off Eleuthera, northeast of Nassau, Northern Bahamas

LOCATION

Rio de Janeiro, southeastern Brazil

One of the most famous beaches in the world, Copacabana Beach is a wide, gently curving stretch of sand between two headlands. Behind the beach lies the city of Rio de Janeiro, with green, luxuriant hills in the hinterland. The beach is crowded much of the year and is known for its beach sports and New Year’s Eve firework displays. The sea area off the beach is not always recommended for swimming, due to strong currents.

Pink Sands in the Bahamas is a gently sloping beach that faces east onto the Atlantic Ocean. It is protected from ocean currents by an outlying reef. The pale pink color of the sand comes from small, singlecelled organisms called foraminiferans, in particular, the species Homotrema rubrum, also known as the sea strawberry. The shells of these organisms are bright red or pink due to the presence of an iron salt. In parts of the Bahamas they are abundant, living on the underside of reefs. When they die, they fall to the seafloor, where they are broken by wave action and mixed with other debris, such as the white shells of snails and sea urchins, as well as mineral grains. This mixture is then finely pulverized and washed up on the shore as pink-colored sand by wave action. GENTLE SLOPE

Pink Sands is an example of a dissipative beach, on which waves break some distance from the shore, then slowly roll in, dissipating their energy across a broad surf zone.

ATLANTIC OCEAN NORTHEAST

St. Ninian’s Tombolo TYPE

Tombolo COMPOSITION

Yellow and white sand LENGTH 1/2

mile (700 m)

West coast of southern Mainland, the main island of the Shetland Isles, off Scotland, UK

OCEAN ENVIRONMENTS

LOCATION

NARROW CONNECTION

A slim, sandy tombolo extends from the Shetland island of Mainland in the foreground, to St. Ninian’s Isle.

COPACABANA LOOKING NORTH

St. Ninian’s Isle in the Shetland Isles provides a classic example of a tombolo, or ayre—a short spit of sedimentary material that connects an island to a nearby land mass or mainland. A tombolo is formed by waves curving around the back of an island so that they deposit sediment on a neighboring land mass, at the point directly opposite the island. Over time, these sediments gradually build up into a tombolo, which

typically projects at right angles to the coast and has a beach on each side. St. Ninian’s Tombolo has been in existence for at least 1,000 years, and its permanence may be due to a cobble base underlying the sand. This tombolo tends to become lower and narrower during storms as a result of destructive wave action, while during calmer weather the waves build it up again with sand carried from offshore or the nearshore. The sediment that

forms a tombolo may come from the mainland, the island, the sea floor, or a combination. Scientists have deduced that a tombolo will usually form when the island’s distance from the shore is less than two-thirds of its length parallel to the shore (the distance of St. Ninian’s Isle from the shore is only about one third of its length). In other cases, a feature called a salient may form—a sand spit that extends toward the island but does not quite reach it.

109 ATLANTIC OCEAN NORTHEAST

North Jutland Dunes TYPE

Coastal dunes

Yellow sand, marram grass

COMPOSITION

LENGTH

155 miles

(250 km) LOCATION

North and northwest coast of Jutland,

Denmark

Much of the northern coastline of Denmark’s Jutland Peninsula consists of sand dunes, which cover several thousand square miles of coast. These dunes are “active” in that they have a natural tendency to migrate along the

ATLANTIC OCEAN NORTHEAST

Porthcurno Beach TYPE

Pocket beach

COMPOSITION

Yellow-white sand, composed mainly of shell fragments LENGTH

500 ft (150 m)

Southwest of Penzance, Cornwall, southwestern England, UK

LOCATION

Porthcurno is a typical pocket beach located near Land’s End at England’s southwesternmost tip. Like all pocket beaches, it nestles between two headlands that protect the sandy cove from erosion by winter storms and strong currents. Pocket beaches are

coast, carried by wind (sand drift) and wave erosion. In some areas, attempts have been made to restrict this dune drift, to prevent sand from inundating summer houses. Some early attempts were fruitless. For example, sand fences were built into the dunes during World War II, but the dunes have since moved behind them, leaving the fences on the beach. More recently, many dune areas have been stabilized more successfully by planting with grasses and conifer trees. SHIFTING SANDS

Many sand dunes on the peninsula have marram grass growing in them, which helps constrain their movement.

common where cliffs made of different types of rock are subject to strong wave action. Rock that is especially hard and resistant to erosion forms headlands, while intervening areas of softer rock are worn down to form pocket beaches. Unlike other beaches, pocket beaches exchange little or no sand or other sediment with the adjacent shoreline, because the headlands prevent longshore drift. The sea at Porthcurno is a distinctive turquoise, possibly due to the reflective qualities of the sand, which is made mainly of shell fragments.

ATLANTIC OCEAN NORTHEAST

Chesil Beach TYPE Storm beach on tombolo COMPOSITION

CHESIL BANK

The bank is about 560 ft (170 m) wide and 50 ft (15 m) high along its entire length. The beach (left) is on its seaward side.

Gravel of

flint and chert LENGTH

LOCATION

18 miles (29 km)

West of Weymouth, Dorset, southern

England

Chesil Beach forms the seaward side of the Chesil Bank, a remarkably long, narrow bank of sedimentary material that connects the coast of Dorset in southern England to the Isle of Portland. Behind the bank is a tidal lagoon called the Fleet. Running parallel to the coast, Chesil Bank looks like a barrier island. However, because it connects the mainland to an island, it is classified as a tombolo. How Chesil Bank and its beach originally formed is debated—the most widely accepted theory is that it originally formed offshore and was then gradually moved to its current location by waves and tides. The beach is classified as a storm beach, as it is affected by strong waves because it faces southwest toward the Atlantic and the prevailing winds. Like most storm beaches, it is steep, with a gradient of up to 45 degrees, and is made of gravel.

GRANITE HEADLANDS

The headlands on either side of the beach are formed from 300- million-year-old granite. DISCOVERY

Chesil Beach’s pebbles change in size progressively from potatosized at one end to pea-sized at the other. This reveals the differences in wave energy along its length—at one end, strong waves wash smaller pebbles offshore; at the other, weaker waves wash them onshore.

OCEAN ENVIRONMENTS

GRADED PEBBLES

110 ATLANTIC OCEAN NORTHEAST

Cap Ferret

ATLANTIC OCEAN EAST

Banc d’Arguin a spit

TYPE Coastal dunes and tidal flats

Sand, grasses, forest

sand

TYPE

Coastal dunes on

COMPOSITION

LENGTH

COMPOSITION

71/2 miles (12 km)

LENGTH

Yellow

100 miles

(160 km) LOCATION

Coast of Aquitaine, southwest of Bordeaux, southwestern France

LOCATION

Between Nouakchott and Nouadhibou on the northwest coast of Mauritania, West Africa

Cap Ferret lies at the southern end of a long sand spit in western France. It separates the Arcachon Lagoon from the Atlantic Ocean and forms part of the spectacular Aquitaine coast, which at 143 miles (230 km) is the longest sandy coast in Europe. This region is characterized by a series of straight, sandy beaches backed by longitudinal sand dunes, which are the highest dune formations in Europe. They include the highest individual European sand dune, the Dune du Pilat, which rises to about 380 ft (115 m) above sea level. Behind the main dune area is a forest, originally planted in the 18th century to try to prevent the dunes from shifting. Unfortunately, this coast is undergoing serious erosion, of more than 33 ft (10 m) a year in some places, mainly because excessive urban development has degraded the vegetation cover.

The Banc d’Arguin National Park is a vast region of dunes, islands, and shallow tidal flats covering more than 4,600 square miles (12,000 square km) of the Mauritanian coast. The dunes, which consist mainly of windblown sand from the Sahara, are concentrated in the southern region of the Park. Banc d’Arguin contains a variety of plant life and is a major breeding or wintering site for many migratory birds, including flamingos, pelicans, and terns. It was declared a World Heritage Site in 1987.

SAND MOUNTAINS

INDIAN OCEAN SOUTHWEST

Jeffreys Bay TYPE Series of gently sloping, dissipative beaches COMPOSITION LENGTH

Sand

9 miles (15 km)

LOCATION West of Port Elizabeth, eastern Cape Province, South Africa

Jeffreys Bay is famous both as a highly popular surfing spot and for the large numbers of beautiful seashells that wash up on its shores. It consists of a series of wide beaches strung out along a southeast-facing stretch of the South African coastline. As a surfing destination, Jeffreys Bay is regularly ranked among the top five beaches in the world by those seeking the “perfect wave.” The most acclaimed surfing spot or wave “break”

Along the coast to the north and south of Cap Ferret, mini-mountains of pale, rippling sand are backed by an extensive vegetation cover.

SAND BANKS AT BANC D’ARGUIN

is known as Supertubes. Here, the combination of shoreline shape, bottom topography, and direction of wave propagation regularly generates waves that form huge, glassy-looking hollow tubes as they break. Other nearby wave breaks in Jeffreys Bay have been given such colorful names as Boneyards, Magna Tubes, and Kitchen Windows. Some of these waves can carry a skilled surfer several hundred yards along the beach on

a single ride. The same waves that attract surfers are also responsible for the vast numbers and wide variety of seashells that are washed up onto the beach with each tide. Conchologists have identified the shells of over 400 species of marine animals, including various gastropods, chitons, and bivalves, making the bay the most biologically diverse natural coastline in South Africa. Dolphins, whales, and seals are also seen. HUMAN IMPACT

OCEAN ENVIRONMENTS

HIDDEN DANGERS

HEADING FOR SUPERTUBES

The waves at Supertubes may be 10 ft (3 m) high and invariably break right-to-left as viewed from the shore.

Every surfing spot, including Jeffreys Bay, has dangers that would-be surfers should know about. The most important are rip currents. The enormous volume of seawater washed up on shore by the waves tends to pool at specific points on the beach and is then funneled back out to sea in swift currents. These move rapidly away from the beach, straight out through the surf zone, and can sweep unsuspecting swimmers out to sea. They can be escaped by swimming parallel to the shore. At Jeffreys Bay, there have also been rare reports of surfers being bitten by sharks, most often by the sand tiger or ragged-tooth shark.

BEACHES AND DUNES INDIAN OCEAN NORTH

INDIAN OCEAN NORTH

Anjuna Beach

Cox’s Bazar Beach

Series of embayed beaches

Dissipative coastal plain beach

TYPE

COMPOSITION

TYPE

Yellow

COMPOSITION

sand LENGTH

111

Yellow

sand 1 mile

LENGTH

(1.5 km)

75 miles

(120 km)

LOCATION

On the Arabian Sea coast, northwest of Panaji, southwestern India

LOCATION

South of Chittagong, southeastern Bangladesh

Anjuna Beach is one of the most scenic and popular of the renowned string of beaches that lie on the coast of the Indian State of Goa. The beach has an undulating shape and is broken up into several sections by rocky outcrops that jut into the sea. By reducing rip currents and crosscurrents, these outcrops help to make Anjuna one of the safest swimming beaches on the Goa coast. During the monsoon season, from June to September, much of the beach sand is stripped away and carried offshore by heavy wave action, but after the monsoons, calmer seas restore the sand deposits.

Cox’s Bazar Beach lies on a northeastern stretch of the Bay of Bengal and is the second-longest unbroken natural beach in the world —Ninety Mile Beach (see p.112) in Australia is the longest. It fronts a range of dunes and, at its southern end, a spit of land. The dunes, spit, and beach have been built up over hundreds of years through a combination of wave action and deposition of sediment from the Bay of Bengal. This is a gently sloping beach that offers safe swimming and surfing and is also popular among collectors of conch shells.

PICTURESQUE SETTING

With its calm seas and sand crescents backed by swaying palms and low, rocky hills, Anjuna has been a favored vacation destination since the 1960s.

SATELLITE VIEW OF BEACH (BOTTOM RIGHT)

INDIAN OCEAN SOUTHEAST

Shell Beach TYPE

Embayed beach

Shells of a species of cockle COMPOSITION

70 miles (110 km)

LENGTH

LOCATION

Northwest of Perth, Western Australia

SHELL BANK

Individual shells in the beach are about ½ in (1 cm) wide. Accumulations of these shells over about 4,000 years has led to the formation of a long bank along the seashore.

OCEAN ENVIRONMENTS

Shell Beach, in Western Australia’s Shark Bay, has a unique composition, consisting almost entirely of the white shells of Fragum erugatum, a species of cockle (a bivalve). The beach lies in a partially enclosed area of Shark Bay known as L’Haridon Bight. This cockle thrives here because its predators cannot cope with the high salinity of the seawater. On the foreshore of Shell Beach, the layer of shells reaches a depth of 26–30 ft (8–9 m). The shells also form the sea floor, stretching for hundreds of yards from the shoreline. On the backshore, away from the water line, many of the shells have become cemented together, in some areas leading to the formation of large, solid conglomerations. These were formerly mined to make decorative wall blocks.

112

COASTS AND THE SEASHORE PACIFIC OCEAN SOUTHWEST

Ninety Mile Beach TYPE Dissipative coastal plain beach COMPOSITION

Yellow

sand LENGTH

90 miles

(145 km) LOCATION Southeast of Melbourne, Victoria, southeastern Australia

Australia’s Ninety Mile Beach, on the coast of Victoria, has a solid claim to be the world’s longest uninterrupted natural beach. The beach runs in a southwest to northeasterly direction

and fronts a series of dunes. Waves generally break too close to the beach for good surfing, and strong rip currents make the conditions hazardous for swimmers. In its northeastern part, several large lakes and shallow lagoons, known as the Gippsland Lakes, lie behind the dunes. Beneath the sea, vast plains of sand stretch in every direction and are home to a large variety of small invertebrate life, including crustaceans, worms, and burrowing mollusks. AERIAL VIEW

Facing out onto the Bass Strait, Ninety Mile Beach is subject to strong waves during the winter months.

PACIFIC OCEAN SOUTHWEST

Moeraki Beach TYPE

PACIFIC OCEAN CENTRAL

Punalu’u Beach

Embayed beach

COMPOSITION

TYPE

Pocket beach

Dark

sand and large boulders LENGTH

COMPOSITION

Black sand

2 miles (3 km)

LENGTH 1/3

Northeast of Dunedin, southeastern New Zealand

LOCATION

The beach north of Moeraki on New Zealand’s South Island is strewn with groups of large, near-spherical boulders. Scientists believe they are mineral concretions that formed over a few million years within 60-million-year-old mudstones— thick layers of sedimentary rock making up the sea floor. These mudstones were later uplifted and now form a cliff at the back of the beach. There, gradual erosion exposes and releases the boulders, which eventually roll down onto the beach.

Punalu’u Beach on Hawaii’s Big Island is a steeply shelving pocket beach. It is best known for its dramatic-looking black sand, which is composed of grains of the volcanic rock basalt. The sand has been produced by wave action on local cliffs of black basaltic lava. Punalu’u, in common with about half the land area of Hawaii, lies on the flank of Mauna Loa, the world’s most massive volcano. Lava produced by the volcano dominates the local landscape—although no lava has reached Punalu’u from Mauna Loa or the nearby active volcano Kilauea for several hundred years. The beach is a popular location for swimming and snorkeling, but underwater springs that eject cold water into the sea close to the beach can cause discomfort. Punalu’u Beach is also visited by green turtles, which come to eat seaweed off rocks at the edge of the beach and bask on the warm, heat-absorbing sand.

SUPERSIZED BOULDERS

The boulders are up to 7 ft (2.2 m) in diameter, and some weigh several tons. Some are half-buried in the sand.

PACIFIC OCEAN NORTHEAST

Columbia Bay TYPE Series of embayed beaches

OCEAN ENVIRONMENTS

COMPOSITION

Gravel

and rocks LENGTH

location by ancient glaciers, remaining there when the glaciers melted. The till has usually been reworked by wave action, with the lighter material (clay, silt, and sand) washed away and the heavier gravel and rocks sorted by size and deposited in different areas along

mile (500 m)

LOCATION

the shoreline. Such is the case in Columbia Bay, a region within Alaska’s Prince William Sound. Many of the beaches in this area have old tidal lines visible above the present ones, the result of a huge earthquake in 1964 that raised the land by 8 ft (2.4 m).

Northeast of Naalehu, Big Island, southeastern Hawaii

31 miles (50 km)

LOCATION Southwest of Valdez, southern Alaska, US

Many beaches in southern Alaska, and other beaches at high latitudes in the Northern Hemisphere, consist of gravel, small rocks, and boulders. These materials come from coarse glacial till—mixtures of clay, silt, sand, gravel, and rocks that were carried to a BEACH AND BAY

BLACK AND BLUE

The backshore area visible here, which has been colonized by plants, was foreshore prior to the 1964 earthquake.

The sand on Punalu’u is almost perfectly black, contrasting with the deep blue Pacific waters. Removal of the sand is prohibited.

BEACHES AND DUNES PACIFIC OCEAN NORTHEAST

Oregon National Dunes TYPE

Coastal dunes

Yellow sand, grasses, conifers

COMPOSITION

LENGTH

40 miles

(64 km) Southwest of Portland, Oregon, northwestern US

LOCATION

Oregon National Dunes is the largest area of coastal sand dunes in North America, extending along the coast of Oregon between the Sislaw and Coos rivers. These dunes have been created through the combined effects of coastal erosion and wind transport of sand over millions of years and extend up to 21/2 miles (4 km) inland, rising to 500 ft (150 m) above sea level. A continuum of dry and wet conditions extends through the dune area. Close to the beach are low foredunes of sand and driftwood

stabilized by marram grass. Behind these are hummocks where sand collects around vegetation. Water accumulates around the hummocks seasonally, giving them the appearance of floating islands. Behind the hummocks are further distinct regions, ranging from densely vegetated areas that become marshlike in winter to completely barren, wind-sculpted high dunes. The dunes are a popular location for various recreational activities, including riding all-terrain vehicles (ATVs) and dune buggies.

113

HUMAN IMPACT

DUNE DESTABILIZATION The use of dune buggies and ATVs, especially when raced in large numbers, may destroy the grass on the dunes, making them susceptible to wind scour. This may in turn lead to self-propagating breaches in the dune ridges. To protect the dunes, ATV usage is restricted.

SEA OF DUNES

The wind molds the sand of the dunes into wave shapes, with crests at right angles to the wind direction.

PACIFIC OCEAN NORTHEAST

Dungeness Spit TYPE

Sand spit COMPOSITION

Sand LENGTH

51/2 miles (9 km) Northwest of Seattle, Washington State, northwestern US

LOCATION

Dungeness Spit, one of the world’s longest natural sand spit, juts out from the Olympic Peninsula in Washington State. It is part of the Dungeness

National Wildlife Refuge and is as little as 100 ft (30 m) wide in places. In addition to its great length, the spit has a complex shape, the result of seasonal changes in wind and wave direction. During part of the year, these bring sandy sediments from the northwest, and at other times from the northeast. The resulting pattern of sedimentation has created a large sheltered coastal area, providing refuge for many shorebirds and waterfowl, which nest along the beach, and for Pacific harbor seals. The tidal flats nourish a variety of shellfish, and the inner bay is an important nursery habitat for several salmon species.

Tamarindo Beach TYPE

Embayed beach COMPOSITION

Yellow sand LENGTH

2 miles

(3 km) LOCATION

Northwest of San José, northwestern

Costa Rica

GROWING SPIT

The spit grows at about 15 ft (4.5 m) a year. It provides shelter for a large inner bay and an area of tidal flats.

Tamarindo Beach is a curved, gently shelving crescent of sand situated close to a mangrove-lined estuary and backed by modern dwellings within

In this view, the main part of Tamarindo Beach is in the background, with the entrance to an estuary that curves around behind the beach on the right.

a scattered forest. It faces directly onto the Pacific, with its enormous fetch (wave-generation area), and so benefits from a strong year-round incoming swell, making the beach a popular surfing location. To the north and south of the main beach are two further beaches that together form the Las Baulas National Marine Park. These are important nesting sites for the leatherback turtle from October to March.

OCEAN ENVIRONMENTS

COASTAL SETTING

PACIFIC OCEAN EAST

114

COASTS AND THE SEASHORE

Estuaries and Lagoons ESTUARIES AND COASTAL LAGOONS ARE BOTH

semi-enclosed, coastal bodies of water. An estuary typically connects to the open sea, is quite narrow, and receives a significant input of fresh water from one or more rivers. This fresh water mixes with the salt water to a varying degree, depending on river input and tides. Many estuaries are simply the seaward, tidally affected ends of large rivers. Coastal lagoons are usually linked to the sea only by one or more narrow channels, through which water flows in and out; sometimes these channels open only at high tide.

Estuary Formation Estuaries form in four main ways. First, sea level may rise and flood an existing river valley on a coastal plain, such as in Chesapeake Bay in the US. Second, sea level can rise to flood a glacier-carved valley, forming a fjord. Estuaries formed in this way are deeper than other types, but have shallow sills at their mouths that partially block inflowing seawater. Third, coastal wave action can also create an estuary, by building river a sand spit or bar across the open end of a bay fed by a stream or river (see p.93). Fourth, estuaries result from movement at tectonic faults (lines of weakness) in Earth’s crust, where downward slippage can result in a surface depression. This becomes an estuary if DROWNED RIVER SYSTEM seawater later floods in. retreating glacier-carved glacier

estuary

delta

sill

valley

FORMATION PROCESSES

CONGO RIVER ESTUARY

Formed by flooding of a river valley, this estuary is the world’s second largest (after the Amazon) in terms of discharge rate.

An estuary can form when sea-level rise causes the seaward end of a river valley to flood (top) or inundates a glacier-carved valley to create a fjord (middle), or when a spit extends across a bay (bottom).

debris left by glacier (moraine)

estuary (fjord)

FLOODED GLACIAL VALLEY sand spit bay estuary river longshore current SPIT ACROSS A BAY

OCEAN ENVIRONMENTS

Types of Estuaries The way in which fresh and salt water mixes in an estuary determines its classification. A strong river inflow usually means minimal mixing—the less-dense fresh water flows over the denser salt water, which forms a wedge-shaped intrusion into the bottom of the estuary. This is a salt-wedge (river-dominated) estuary. In partially mixed and fully mixed (tide-dominated) estuaries, there is considerable mixing, producing turbulence and increased salinity in the fresh water. In each case, this is balanced by a strong, tidally influenced influx of salt water from the sea: this influx brings sediments from offshore, which are deposited as mud in the estuary. medium flow of fresh water

minimal mixing of salt and fresh water

strong flow of fresh water

SALT-WEDGE ESTUARY

In a salt-wedge estuary (left), there is a strong flow of fresh river water over a wedge of salt water, with little mixing between the two layers.

fresh water

wedge of sea water

horizontal variation in salinity weak flow of fresh water

outflow to sea

slightly salty water flows out

small tidal countercurrent outflow to sea large tidal countercurrent

fresh water

considerable mixing

PARTIALLY MIXED ESTUARY

large tidal countercurrent

In this type of estuary, there is considerable mixing between fresh and salt water. The saltiness of the water increases with depth in all parts of the lower estuary.

thorough vertical mixing

salt water

FULLY MIXED ESTUARY

In a fully mixed (or tide-dominated) estuary, the fresh and salt water are well-mixed vertically, but there is some horizontal variation in saltiness.

ESTUARIES AND LAGOONS CARVED BY GLACIERS

A fjord is an estuary formed when the sea floods a deep valley originally carved out by a glacier. Norway’s Geiranger Fjord is 12 miles (20 km) long, and reaches a depth of 660 ft (200 m).

115

Estuarine Environments Estuaries are unique coastal environments. They are typically long and funnel-shaped, so tides don’t just rise here—they rush in, creating strong currents and, sometimes, wall-like waves called tidal bores. The high COMMON EUROPEAN OYSTER rate of sedimentation means that mud accumulates, so tidal mudflats and salt marshes (see pp.124–25) or in the tropics, mangrove swamps (see pp.130–31), develop. Despite the effects of tides and currents, the high turbidity that reduces plant photosynthesis, and fluctuations in salinity and temperature, most estuaries are biologically highly productive. This is partly due to the high concentration of nutrients in river water, and because estuaries are well oxygenated. Although only a limited range of organisms, such as mussels, cope with living in estuaries, populations are often huge.

RICH FOOD SOURCE

ESTUARY DWELLER

Estuaries attract waders and other shorebirds because of the high concentrations of small animals (such as worms and shrimp) that live in the mud deposits. These lapwings and an egret are congregating to feed in the Thames estuary, UK.

Various species of starfish tolerate the estuarine environment, where they feed on mussels, crustaceans, and worms. This common starfish is in an estuary in Brittany, France.

Coastal Lagoons Coastal lagoons occur worldwide, and are different from the lagoons found at the centers of coral atolls (see p.152). Calmer and usually shallower than estuaries, most lagoons are connected to the sea by tidal channels. Although fresh water does not usually flow into coastal lagoons, some do receive a significant river inflow. So, as well as saltwater lagoons, there are also some partly, or predominantly, freshwater lagoons. In hot climates, some lagoons are hypersaline (saltier than ocean water), due to high evaporative losses. Although some coastal lagoons are severely polluted, the cleaner ones are often well stocked with fish, crustaceans, and other marine life, and frequently attract large numbers of shorebirds. Some provide feeding or breeding areas for sea turtles and whales.

Matagorda Bay is a lagoon on the coast of Texas, separated from the Gulf of Mexico by a long, narrow peninsula. Two channels, located near the southwest corner of the lagoon, connect it to the gulf.

OCEAN ENVIRONMENTS

LAGOON AND CHANNELS

116

COASTS AND THE SEASHORE ATLANTIC OCEAN NORTHWEST

St. Lawrence Estuary TYPE Salt-wedge (river-dominated) estuary

Approximately 10,000 square miles (25,000 square km)

AREA

LOCATION

Quebec, eastern Canada

The St. Lawrence Estuary is one of the world’s largest estuaries. Some 500 miles (800 km) long, it discharges about 3 million gallons (12 million liters) of water into the Gulf of St. Lawrence each second. The estuary is rich in marine life. In its wide middle and lower reaches, the icy Labrador Current flows 1,000 ft (300 m) below the surface in the opposite direction of the main estuarine flow. In one section, near the mouth of a fjord that branches off the estuary, the current’s nutrientrich waters rise abruptly and mix with warmer waters above. This upwelling of nutrients encourages plankton growth, providing the base of a food chain that involves many species of fish and birds, and a small population of beluga whales. WINTER SCENE

In winter, much of the estuary becomes iced over. A stretch of the estuary is seen here at low tide, shortly after sunrise.

ATLANTIC OCEAN NORTHWEST

Chesapeake Bay TYPE

Partially mixed estuary AREA

3,200 square miles (8,200 square km)

OCEAN ENVIRONMENTS

LOCATION Surrounded by Maryland and parts of eastern Virginia, US

Chesapeake Bay is the largest estuary in the US. Its main course, fed by the Susquehanna River, is over 185 miles (300 km) in length. It has numerous sub-estuaries, and more than 150 rivers and streams drain into it. This body of water was created by sea-level rise drowning the valley of the Susquehanna and its tributaries over the last 15,000 years. Once famous for its seafood, such as oysters, clams, and crabs, the bay is now far less

productive, though it still yields more fish and shellfish than any other estuary in the US. Industrial and farm waste running into the bay causes frequent algal blooms, which block sunlight from parts of its bed. The resulting loss of vegetation has lowered oxygen levels in some areas, severely affecting animal life. The depletion of oysters, which naturally filter water, has had a particularly harmful effect on the bay’s water quality.

BAY BRIDGE

DISCOVERY

A major bridge in the upper bay connects Maryland’s rural eastern shore to its urban western shore.

IMPACT CRATER In the 1990s, drilling of the seabed at Chesapeake Bay led to the discovery of a meteorite impact crater 53 miles (85 km) wide under its southern region. The 35-million-year-old crater helped shape today’s estuary.

SHOCKED QUARTZ

Evidence for the crater included the discovery of grains of shocked quartz, which forms when intense pressure alters its crystalline structure.

MAIN CHANNEL FLOWING THROUGH DELTA ATLANTIC OCEAN WEST

Mississippi Estuary TYPE

Salt-wedge (river-dominated) estuary AREA

25 square miles (60 square km) Southeastern Mississippi Delta, southeastern Louisiana, US

LOCATION

The Mississippi Estuary is about 30 miles (50 km) long and lies at the seaward end of the Mississippi River, where the river flows through its own delta. The estuary consists of a main channel and several subchannels. Together, these discharge an average of some 4.75 million gallons (18 million liters) of water per second into the Gulf of Mexico. The main channel is a classic example of a salt-wedge estuary—its surface waters contain little salt, but they flow over a wedge of salt water, which extends deep down for several miles up the estuary.

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ATLANTIC OCEAN WEST

Laguna Madre TYPE

Hypersaline coastal lagoon AREA

14,400 square miles (3,660 square km) Southern Texas, US, and northeastern Mexico, along the coast of the Gulf of Mexico

LOCATION

The Laguna Madre is a shallow lagoon in two distinct parts extending about 285 miles (456 km) along the coast of the Gulf of Mexico. Its northern part, in Texas, is separated from the Gulf by a long, thin barrier island, Padre Island. The southern part, in Mexico, is

similarly cut off by a string of barrier islands. The entire lagoon connects with the Gulf only via a few narrow channels, and it is less than 3 ft (1 m) deep in most parts. It is saltier than seawater because it receives no input of river water and lies in a hot, dry region, leading to high rates of evaporation. Seagrass meadows and several species of crustaceans and fish thrive in the lagoon, which also supports many wintering shorebirds and waterfowl. Threats to the lagoon’s health include dredging, overfishing, and algal blooms. FLY-FISHING FOR REDFISH

The sale of licenses for fly-fishing—for trout and redfish—in the Laguna provides funds for protecting its water quality and wildlife.

ATLANTIC OCEAN SOUTHWEST

Lagoa dos Patos TYPE

Tidal coastal lagoon AREA

3,900 square miles (10,000 square km)

LOCATION

South of the city of Porto Alegre, southern

Brazil

TWO LAGOONS

In this aerial view, Lagoa dos Patos is the pale central area. Below it, the darker Mirim Lagoon extends to the Brazil–Uruguay border.

OCEAN ENVIRONMENTS

Lagoa dos Patos (“Lagoon of Ducks”) is the world’s largest coastal lagoon. Its name is said to have been given to it by Jesuit settlers in the 16th century, who bred waterfowl on its shores. It is a shallow, tidal body of water, 155 miles (250 km) long and up to 35 miles (56 km) wide. A sand bar separates it from the Atlantic, with which it connects at its southern end via a short, narrow channel that disgorges a large plume of sediment into the ocean. Marine animals use this channel to access the lagoon; sea turtles are found in the lagoon in spring and summer. At its northern end, the lagoon receives an inflow of fresh water from the Guaíba Estuary, formed from the confluence of the Rio Jacui and three smaller rivers. Along its inner side are a number of distinctive wavelike “cusps” that have been caused by the accumulation and erosion of

sediments driven by tidal action and winds. The salinity of the lagoon varies. It consists mainly of fresh water at times of high rainfall, but there is considerable saltwater intrusion at its southern end at times of drought. Lagoa dos Patos is one of Brazil’s most vital fishing grounds. However, run-off from rice fields and pastureland, industrial effluents, and increasing population have led to concerns for the lagoon’s ecosystem.

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COASTS AND THE SEASHORE ATLANTIC OCEAN SOUTHWEST

Amazon Estuary TYPE Salt-wedge (river-dominated) estuary

Approximately 7,800 square miles (20,000 square km)

AREA

LOCATION

Northern Brazil HUMAN IMPACT

The Amazon Estuary is a stretch of the Amazon River that extends more than 190 miles (300 km) inland from the river’s mouth to an area southwest of the city of Macapà.Varying in width from 15 to 190 miles (25 to 300 km), the estuary is partly filled by numerous low-lying, forested islands. The Amazon Estuary has by far the largest water output of any estuary in the world, discharging an average of 45 million gallons (200 million liters) per second into the Atlantic. The sheer magnitude of this discharge means that, almost uniquely among estuaries, there is very little saltwater intrusion into it. Instead, nearly all of the mixing between the river’s discharge and seawater occurs outside the estuary, on an area of continental shelf. Despite the relative lack of seawater intrusion, the whole estuary is significantly affected by twice-daily tides, which cause inundation (by river water) of most of the islands in the estuary.

POROROCA SURF Tidal bores, locally called pororocas, occur on large spring tides in several of northern Brazil’s river estuaries. Some of these bores attain heights of 10 ft (3 m) and can be surfed for several miles. This sport is rather hazardous, however, because the waters through which the pororocas surge are home to dangerous snakes, fish, and crocodiles.

MARAJO ISLAND

The Amazon Estuary is so enormous that the biggest of the forested islands lying within it, Marajo Island, has its own river system.

ATLANTIC OCEAN SOUTHWEST

River Plate TYPE

Salt-wedge (river-dominated) estuary AREA

13,500 square miles (35,000 square km)

OCEAN ENVIRONMENTS

LOCATION On the Argentina–Uruguay border, east of Buenos Aires and southwest of Montevideo

SATELLITE VIEW

The main flow of river water over the sediments on the estuary bed is visible here, as well as the Paraná River at top left and the Uruguay River at top center.

The Plate River, or Rio de la Plata, is not a river but a large, funnel-shaped estuary formed by the confluence of the rivers Uruguay and Paraná. These rivers and their tributaries drain about one-fifth of the land area of South America. At 180 miles (290 km) long and 136 miles (220 km) wide at its mouth, the Plate discharges about 6.5 million gallons (25 million liters) of water per second into the Atlantic Ocean. As well as transporting this

vast amount of water, the estuary receives about 2 billion cubic feet (57 million cubic meters) of silt each year from its input rivers. This mud accumulates in great shoals, so that the water depth in most of the estuary is less than 10 ft (3 m). Constant dredging is therefore needed to maintain deep-water channels to the ports of Buenos Aires, which lies near the head of the estuary, and Montevideo, which is close to its mouth. Surface salinity

varies uniformly through the estuary, from close to zero in its upper parts to a value just below average ocean salinity near its mouth. Deep down, a wedge of salt water penetrates deep into the estuary. Biologically, the Plate is highly productive, yielding large annual masses of plankton, which support large numbers of fish and dense beds of clams. It is also a habitat for the La Plata Dolphin, an endangered long-beaked species of river dolphin.

119 ATLANTIC OCEAN NORTHEAST

Curonian Lagoon TYPE

Freshwater coastal lagoon AREA

610 square miles (1,580 square km) On the Baltic Sea coasts of Lithuania and the Kaliningrad Oblast (part of Russia)

LOCATION

The Curonian Lagoon is a nontidal lagoon on the southeastern edge of the Baltic Sea, with an average depth of just 12 ft (3.8 m). The Neman River flows into the lagoon’s northern (Lithuanian) section, which discharges into the Baltic via a narrow channel, the Klaipeda Strait. While most of the lagoon consists of fresh water, seawater sometimes enters its northern part via the Klaipeda Strait following storms. In the past, the lagoon has suffered heavy

pollution from sewage and industrial effluents, but attempts are now being made to address this problem. The lagoon is separated from the Baltic by the narrow, curved Curonian Spit, which is 60 miles (98 km) long. The spit is notable for its mature pinewoods and drifting barchans (sand dunes), some reaching a height of 200 ft (60 m), which extend for 20 miles (31 km) along the spit. The sandy beaches on the spit, together with vistas over the lagoon, woods, and drifting dunes, make it a tourist attraction, and in 2000 the entire spit was designated a UNESCO World Heritage site. DUNES AND LAGOON

This quiet corner of the northern part of the lagoon is backed by the Curonian Spit’s high dunes. Migrating birds use the lagoon and nearby Neman Delta for vital rest breaks.

ATLANTIC OCEAN NORTHEAST

Hardanger Fjord TYPE Highly stratified estuary; fjord

Approximately 290 square miles (700 square km)

AREA

LOCATION

Southeast of Bergen, southwestern

Norway

READS ISLAND

This low-lying island, in the upper part of the estuary, is a breeding ground for avocets and other rare birds and is managed as a nature reserve. The view here is looking downstream.

Humber Estuary Fully mixed (tide-dominated) estuary

TYPE

Approximately 80 square miles (200 square km)

AREA

West and southeast of Kingston-uponHull, eastern England, UK

LOCATION

This large estuary on Great Britain’s eastern coastline is formed from the confluence of the Ouse and Trent rivers. It discharges about 66,000

ATLANTIC OCEAN NORTHEAST

Eastern Scheldt Estuary TYPE

Former estuary, now a sea-arm AREA

140 square miles (365 square km) Southwest of Rotterdam, southwestern Netherlands

LOCATION

The Eastern Scheldt Estuary is a tidal body of water 25 miles (40 km) long, with a salinity similar to that of seawater. Since the late 1980s, it has

The fjord’s narrow upper parts are fed by several spectacular waterfalls, such as the Vøringsfossen, which freefalls 600 ft (182 m).

Hardanger Fjord was formed about 10,000 years ago, when a large glacier that had carved out and occupied a deep U-shaped valley in the area began to melt and retreat. As it did so, seawater flooded into the valley to create the fjord. Today, the fjord continues to receive a large input of fresh water from glacier melt. Throughout much of its length, the fjord is stratified into a lower layer of salt water, which moves into the fjord during flood tide, and an upper layer of fresher water that flows outward to the sea on the ebb tide. been cut off from its input of fresh water from the Scheldt River by dams, leading to its reclassification as a sea-arm rather than an estuary. It has also been defended against seawater flooding by a storm-surge barrier (see p.104). This was originally to have been a fixed dam to prevent any ingress of seawater at all, but there were fears that, with a dam of this type, the estuary would gradually lose its salinity, producing an adverse effect on its fauna and flora—in particular, there were concerns that it would end the large-scale mussel and oyster farming in the area and degrade the tidal flats and salt marshes that form an important habitat for birds. The government of the Netherlands therefore commissioned a movable barrier, the construction of which was completed in 1986. STORM BARRIER GATES

The gates are usually raised, allowing tidal water in and out of the Eastern Scheldt Estuary. They are lowered about twice a year, during stormy weather.

OCEAN ENVIRONMENTS

ATLANTIC OCEAN NORTHEAST

gallons (250,000 liters) of water per second into the North Sea, the largest input from any British river into this sea. After the end of the last ice age, when sea levels were much lower, the Humber was a river that flowed up to 30 miles (50 km) past the present coastline before reaching the sea. About 3.6 million cubic feet (100,000 cubic meters) of sediment are deposited in the estuary every year, mainly from offshore by tidal action. Shifting shoals formed by this sediment can obstruct shipping. The estuary’s intertidal areas are productive ecosystems that support a wide range of mollusks, worms, crustaceans, and other invertebrates. These are vital sources of food for birds, especially waders. The estuary also supports a colony of gray seals, and many lampreys pass through it every year.

Like all fjords, the Hardanger Fjord in Norway is much deeper than a typical coastal-plain estuary, with a maximum depth of some 2,600 ft (800 m). Near its mouth is a sill just 500 ft (150 m) deep. At 114 miles (183 km) long, it is the third-longest fjord in the world.

UPPER FJORD

120 ATLANTIC OCEAN NORTHEAST

Gironde Estuary Fully mixed (tide-dominated) estuary

TYPE

Approximately 200 square miles (500 square km)

AREA

LOCATION

North of Bordeaux, western France

The Gironde Estuary, formed by the confluence of the Garonne and Dordogne rivers, is the largest estuary in Europe at almost 50 miles (80 km) long and up to 7 miles (11 km) wide. The estuary’s average discharge rate into the Atlantic is 265,000 gallons (1 million liters) per second. It has a large tidal range, of up to 16 ft (5 m) during periods of spring tide, and the strong tidal currents in the estuary, as well as numerous sand banks, tend to

hamper navigation. One of the Gironde’s most impressive features is its tidal bore—a large, wall-like wave at the leading edge of the incoming tide—known locally as the Mascaret. Occurring with each flood tide at the time of spring tides (that is, twice daily for a few days every two weeks), the bore surges from the Gironde upstream into its narrower tributaries. On the Garonne, the Mascaret sometimes forms a barreling wave, which can reach a height of 5 ft (1.5 m) and tends to break and reform. The Gironde is an important artery of the Bordeaux wine region and a rich source of eels and a wide variety of shellfish, which feature on local restaurant menus. Wild sturgeon (the source of caviar) were once also plentiful in the estuary, and although their numbers have declined due to overfishing, they are still farmed in small numbers.

THE MASCARET

When it reaches the Dordogne River, the Mascaret, or Gironde tidal bore, turns into a series of waves, which may travel up to 20 miles (30 km) upstream.

ATLANTIC OCEAN EAST

Venetian Lagoon TYPE

Saltwater coastal lagoon AREA

210 square miles (550 square km) LOCATION

On the Adriatic coast of northeastern Italy

The Venetian Lagoon is a very shallow, crescent-shaped coastal lagoon off the northern part of the Adriatic Sea. It is the largest Italian wetland and a major Mediterranean coastal ecosystem.

In addition to Venice, which sits on a small island at the center, the lagoon contains many other islands, most of which were marshy but have now been drained. Its average depth is just 28 inches (70 cm), so most boats cross the lagoon only via dredged navigation channels, and four-fifths of its area consists of salt marshes and mudflats. It takes in both riverine fresh water and seawater, and its tides have a range of up to 3 ft (1 m). During periods of spring tide,Venice is regularly flooded (see p.90), although engineering works designed to prevent this are due to be completed in 2016. Land subsidence and rising sea levels also pose a major

threat to the city and its art treasures. Marine life in the lagoon includes many species of fish (from anchovies to eels, mullet, and sea bass) and invertebrates. Seabirds, waterfowl, and waders proliferate on the many uninhabited islands. Efforts are now being made to reduce industrial and agricultural pollution, including attempts to capture pollutants by means of shrubs planted along the edges of the lagoon. WATERY GEM

In the center of this photograph, taken from the International Space Station, is the fish-shaped main island of Venice. Below it is one of the lagoon’s three protective barrier islands.

JAMES ISLAND

ATLANTIC OCEAN EAST

Gambia Estuary Salt-wedge (river-dominated) estuary

TYPE

Approximately 400 square miles (1,000 square km)

OCEAN ENVIRONMENTS

AREA

LOCATION

East of Banjul, Gambia, West Africa

The Gambia Estuary is the western half of the Gambia River, which runs 700 miles (1,130 km) through West Africa. The estuary is tidal throughout and discharges about 528,000 gallons (2 million liters) per second into the Atlantic during the rainy season, but only 528 gallons (2,000 liters) in the dry season. It contains abundant stocks of fish and shellfish, including catfish, barracuda, and shrimp. Kunta Kinteh Island, or James Island, some 20 miles (30 km) from the estuary’s mouth, was formerly a slave-collection point and is now a UNESCO World Heritage Site.

ESTUARIES AND LAGOONS ATLANTIC OCEAN EAST

Ebrié Lagoon TYPE

Coastal lagoon of variable salinity AREA

200 square miles (520 square km) LOCATION

West of Abidjan, Ivory Coast, West Africa

The Ebrié Lagoon is one of three long, narrow lagoons that line the shores of the West African state of Ivory Coast. With a length of 62 miles (120 km) and an average width of 21/2 miles (4 km), it is the largest lagoon in West Africa. Its average depth is 16 ft (5 m). Near its

eastern end, it connects to the Atlantic via a narrow artificial channel, the Vridi Canal, opened in 1951. Abidjan, the largest city in Ivory Coast, stands on several converging peninsulas and islands in an eastern part of the lagoon; other communities situated on or in the lagoon include the town of Dabou and the village of Tiagba (see below). The Komoé River provides the main input of fresh water. In winter the lagoon becomes salty, but it turns to fresh water during the summer rainy season. Levels of pollution in the lagoon have been high for some years due to dumping of refuse and discharge of untreated industrial effluents and sewage from the nearby urban areas.

INDIAN OCEAN NORTH

Kerala Backwaters TYPE Chain of coastal saltwater lagoons

Approximately 400 square miles (1,000 square km)

AREA

TIAGBA VILLAGE

Southeast of Cochin, Kerala State, southwestern India

LOCATION

In the village of Tiagba, on the outskirts of a small island in the Ebrié Lagoon, the buildings are raised up on wooden piles.

The backwaters of Kerala in southern India are a labyrinth of lagoons and small lakes, linked by 900 miles (1,500 km) of canals. The lagoons are

LAKES AND LAGOON

In this satellite view, the Coorong Lagoon is the narrow blue strip behind the yellow sand dunes. Above are the lakes Alexandrina (left) and Albert (right).

Coorong Lagoon TYPE

Saltwater coastal lagoon AREA

80 square miles (200 square km) Southeast of Adelaide on the southeastern coast of South Australia

LOCATION

The Coorong Lagoon is a wetland that lies close to the coast of South Australia. It is famous as a haven for birds, ranging from swans and pelicans

to ducks, cranes, ibis, terns, geese, and waders such as sandpipers and stilts. The lagoon is separated from the Great Australian Bight (considered part of the Indian Ocean) by the Younghusband Peninsula, a narrow spit of land covered by sand dunes and scrubby vegetation. The lagoon is about 93 miles (150 km) long, with a width that varies from 3 miles (5 km) to just 330 ft (100 m). At its northwestern end, the lagoon meets the outflow from Australia’s largest river, the Murray, after the river has passed through Lake Alexandrina. In this region, called the Murray Mouth, both river and lagoon meet the sea,

and the Coorong can receive both fresh and salty water. The lagoon was once freely connected to the lake, from which it received a much larger supply of fresh water. In 1940, however, barrages were built between the lagoon and the lake to prevent seawater from reaching the lake and the lower reaches of the Murray River. The salinity of the lagoon’s waters increases naturally with distance from the sea due to evaporative losses. However, reduced water flows from the Murray, due to a combination of barrage construction and extraction of water for irrigation projects, has caused a gradual further increase in salinity throughout the

VEMBANAD LAKE

Vembanad, the largest Kerala coastal lagoon, is listed as a Wetland of International Importance under the Ramsar Convention.

shielded from the sea by low barrier islands and spits that formed across the mouths of the many rivers flowing down from the surrounding hills. During the summer monsoon rains, the lagoons overflow and discharge sediments into the sea, but toward the end of the rains, the seawater rushes in, altering salinity levels. The aquatic life in the backwaters, which includes crabs, frogs, otters, and turtles, is well adapted to this seasonal variation.

PELICANS IN DECLINE The Coorong is home to a large breeding colony of Australian Pelicans, which inhabit a string of islands in the center of the lagoon. Since the 1980s, however, their numbers have fallen significantly due to reduced flows of fresh water into the Coorong from the Murray River. The resultant higher salt levels in the lagoon have reduced the growth of an aquatic weed that is a major part of the food chain.

AUSTRALIAN PELICANS

This pelican, one of seven species worldwide, is widespread in Australia, where it lives on freshwater, brackish, and saltwater wetlands.

lagoon. There is ample evidence that this has adversely affected the lagoon’s ecosystem. In particular, several species of plants have become less abundant or disappeared, many fish species have declined, and migratory bird numbers have fallen. Further, the reduced flow from the Murray may result in the eventual closure of the channel joining the lagoon to the ocean, which would prevent migration of fish and other animals between the two.

OCEAN ENVIRONMENTS

INDIAN OCEAN SOUTHEAST

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COASTS AND THE SEASHORE PACIFIC OCEAN WEST

Pearl River Estuary TYPE

Salt-wedge (river-dominated) estuary AREA

1,200 square km (450 square miles) Northwest of Hong Kong, Guangdong, southeastern China

LOCATION

INDIAN OCEAN SOUTHEAST

Northern Spencer Gulf Estuary TYPE

Inverse estuary AREA

Approximately 5,000 square km (2,000 square miles) LOCATION

Northwest of Adelaide, South Australia

The estuary in the north of Australia’s Spencer Gulf is classified as an inverse estuary, owing to its unusual pattern of salt distribution and water circulation.

DEEP GULF

Spencer Gulf is the larger wedge-shaped coastal indent visible in this satellite image. The desert around its head helps produce the estuary’s unusual circulation pattern.

In a reverse of the usual pattern, this estuary’s waters become saltier towards it head, away from its mouth. This is because its head is surrounded by hot desert and loses more water to evaporation than enters it from rivers. The head’s high salinity means that it draws in from the mouth ocean water of lower salinity than the water drawn in by a typical estuary. The estuary is surrounded by extensive tidal flats, seagrass banks, and mangroves.

The bell-shaped Pearl River Estuary receives and carries most of the outflow from the Pearl River, the common name for a complex system of rivers in the southern Chinese province of Guangdong. The estuary is nearly 60km (37 miles) long, and its width increases from 20km (12 miles) at its head to about 50km (30 miles) at its mouth. To the north and west of the estuary is a delta, formed from the confluence of the Xi Jiang and other rivers of the Pearl River system. Together, these rivers discharge an average of GUANGZHOU

Formerly known as Canton, this large and busy port city lies on a northerly extension of the Pearl River Estuary.

PACIFIC OCEAN WEST

Yangtze Estuary TYPE

Partially mixed estuary AREA

2,500 square km (1,000 square miles)

OCEAN ENVIRONMENTS

LOCATION

SHANGHAI YANGTZE RIVER BRIDGE

This bridge across the Yangtze Estuary, situated very close to its mouth, is 10km (6 miles) long. It opened in 2009.

10 million litres (2.2 million gallons) of water per second into the South China Sea. Mostly less than 9m (30ft) deep, but containing some deeper dredged channels, the Pearl River Estuary has a tidal range of 1–2m (3–6ft). It drains water from one of the most densely urbanized regions in the world and is severely polluted as a result of billions of tonnes of sewage and industrial effluent entering it each year. One result of this has been the increasing occurrence of algal blooms that threaten local fishing. Pollution is also a threat to a dwindling population of Chinese White Dolphins (less than 1,000) that live in the estuary. Only since 2008 have efforts begun to reduce pollution through the building of more water treatment plants.

Northwest of Shanghai, eastern China

The Yangtze Estuary is the lower, tide-affected part of the Yangtze (or Changjiang) – the longest river in Asia and the third longest in the world. The estuary occupies 700km (430 miles) of the river’s 6,300-km (3,900-mile) length. Near its mouth, it splits into three smaller rivers and numerous streams that run through a delta. Here, silt deposition continually creates new land, which is used for agriculture. The estuary carries an average of 30 million litres (6.6 million gallons) of water per second into the East China Sea; its average depth is 7m (23ft), and the average tidal range at its mouth is 2.7m (9ft). It supports large numbers of fish and birds, although fish stocks have declined over the past 20 years due to overfishing and pollution. A species of river dolphin that used to live in the estuary, the Baiji or Yangtze River Dolphin, is now thought to be extinct. In winter, salt water intrudes a significant distance upstream, making the water unfit for drinking and irrigation. Recently, this intrusion has occurred more frequently due to reduced river flow – a reduction exacerbated by the Three Gorges Dam project further upstream. Reduced flows have worsened the acute water shortage in Shanghai on the estuary’s southern shore, as well as affected the dispersion and dilution of pollutants around the estuary. Silt deposition in the delta is also likely to fall, reducing the rate of new land creation.

ESTUARIES AND LAGOONS PACIFIC OCEAN SOUTHWEST

Doubtful Sound TYPE

Highly stratified estuary; fiord AREA

70 square km (30 square miles) West of Dunedin, southwestern South Island, New Zealand

LOCATION

Doubtful Sound is one of 14 major fiords that were formed 15,000 years ago in a scenic part of New Zealand’s South Island. Some 40km (25 miles) long and opening onto the Tasman Sea, it is surrounded by steep hills from which hundreds of small waterfalls descend during the rainy season. Its name originated in 1770 during the first voyage to New Zealand by the English explorer Captain James Cook (1728–79). He called the fiord Doubtful Harbour

because he was sceptical of being able to sail out again if he entered it. Doubtful Sound is the second-longest and the deepest of the New Zealand fiords, with a maximum depth of 421m (1,380ft). It receives fresh water from a hydroelectric power station at its head and from a huge 6,000m (236in) of rainfall annually. Like all fiords, it contains fresh water in its top few metres and a much denser, colder, saltier layer below. There is little mixing between the two. Doubtful Sound is home to Bottlenose Dolphins, New Zealand Fur Seals, and many species of fish, starfish, sponges, and sea anemones. SOUND VIEW

This view of the head of Doubtful Sound, looking towards the open ocean, is from the hills of the south-central region of New Zealand’s South Island.

PACIFIC OCEAN NORTHEAST

San Francisco Bay AREA

LOCATION

Central California, western USA

San Francisco Bay, the largest estuary on North America’s west coast, consists of four smaller, interconnected bays. One of these, Suisun Bay, receives fresh water drained from about 40 per cent of California’s land area. This water flows into San Pablo Bay and then Central Bay, where it mixes with salt water that has entered at depth from the Pacific Ocean via the Golden Gate channel. From Central Bay, there is little flow of fresh water to the largest body of water, South San Francisco Bay, but there is

Laguna San Ignacio TYPE

Hypersaline coastal lagoon AREA

360 square km (140 square miles) On the Pacific coast of the Baja California Peninsula, Mexico, southeast of Mexicali

LOCATION

OAKLAND BAY BRIDGE

Thick fog surrounds the lower half of the San Francisco–Oakland Bay Bridge, one of five bridges that cross the bay.

TYPE

Partially mixed tectonic estuary 1,200 square km (460 square miles)

PACIFIC OCEAN EAST

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The Laguna San Ignacio is a coastal lagoon in northwestern Mexico best known as a sanctuary and breeding ground for Pacific Gray Whales. Latin America’s largest wildlife sanctuary, it is also an important feeding habitat for four endangered species of sea turtle. The lagoon, which is 40km (25 miles) long and on average 9km (6 miles) wide, receives only occasional inflows of fresh water, and its evaporative losses are high. Its salinity is therefore

significantly higher at its head than at its mouth, where it connects to the sea. Apart from whale watching, the main human activities in the area are small-scale fisheries and oyster cultivation. In 1993, the lagoon was designated a World Heritage Site. LAGOON BEACH

Waves break on the shore at San Ignacio Lagoon, which is surrounded by a landscape of sparse desert scrub.

some surface outflow of brackish water to the Pacific. San Francisco Bay is a tectonic estuary – one caused by movement at tectonic faults (lines of weakness) in the Earth’s crust, of which there are several in the area, notably the San Andreas Fault. During the past 150 years, human activity has resulted in the loss of 90 per cent of the bay’s surrounding marshy wetland, a greatly reduced flow of fresh water (which has been diverted for agricultural purposes), and contamination by sewage and effluent. Nevertheless, the bay remains an important ecological habitat. Its waters are home to large numbers of economically valuable marine species, such as Dungeness Crab and California Halibut, and millions of geese and ducks annually use the bay as a refuge.

HUMAN IMPACT

WHALE WATCHING

OCEAN ENVIRONMENTS

The Laguna San Ignacio is a popular whale-watching site. Between January and March, large numbers of Gray Whales can be found there. The whales, which often approach boats, use the upper part of the lagoon for giving birth, while the lower lagoon is where males and females look for mates. Females swim with their calves in the middle part of the lagoon.

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COASTS AND THE SEASHORE

Salt Marshes and Tidal Flats A SALT MARSH IS A VEGETATED AREA OF COAST

AT L A

that is partly flooded by the sea at high tide and completely flooded by the highest spring tides. Many areas of salt marsh are bordered by tidal flats. These are broad areas of mud or sand, mainly without vegetation, that are uncovered at low tide and covered as the PA C I F I C tide rises. Salt marshes and tidal flats are depositories for large OCEAN amounts of organic material, derived from decaying plants and animals. This provides the base for an extensive food chain.

N T

IC

O C

EAN

INDIAN OCEAN

HERN OCEAN SOUT

Formation and Features Tidal flats occur on low-energy sheltered coasts, such as estuaries and enclosed bays, where sediment held in the water settles out and builds up. The most extensive flats occur where there is a high tidal range. Tidal flats may consist either of sand (sandflats) or mud (mudflats), or a mixture of these. Mudflats contain a higher concentration of the decaying remains of dead organisms than sandflats and are also the first stage in the development of salt marshes. These develop on the landward side river delta of mudflats. As various salt-tolerant plants grow, their roots trap sediment and stabilize the mud. As the vegetated flat builds up, different mainland types of plants become established. The result is a salt marsh, consisting of blocks of flat, low-growing vegetated areas of mud, broken up by sinuous channels.

DISTRIBUTION

Salt marshes and tidal flats occur only north of the latitude of 32˚N and south of 38˚S. In latitudes nearer the equator, they are replaced by mangrove swamps. COASTAL SETTING

Salt marshes commonly develop in coastal lagoons or in estuarine areas that are sheltered from the sea by spits or barrier islands. The channels transport salt water, plankton, nutrients, sediment, and plant detritus into and out of the marsh.

estuary mainland

channels

flood delta

BAY OF FUNDY

In this small sub-estuary of Canada’s Bay of Fundy, an area of salt marsh is visible in the background. In the foreground is a broad intertidal area of mud and gravel.

dunes

barrier island

KEY

dunes

salt marsh ebb delta

inlet

lagoon

tidal flats

Zones and Evolution

OCEAN ENVIRONMENTS

Salt marshes have two main zones. The parts flooded by every high tide are called low marsh, while the areas that are only occasionally flooded are termed high marsh. Each zone is colonized by distinct species of salt-tolerant plants. Each species, of which there are many, has developed special mechanisms to deal with the high levels of salt they are exposed to: some possess salt-excreting glands, for instance, while others have storage systems for collecting the salt until they can dilute it with water. Salt marshes and adjoining mudflats usually evolve over time. As sediment builds up, the mud surface in the marsh, the adjoining flats, and the bay or estuary as a whole tends to rise. As it does so, areas of low marsh become high marsh and areas of mudflat are colonized by plants, turning into low marsh.

SEA LAVENDER

Sea lavenders are common high-marsh colonizers. They bloom in summer, producing purple or lavender flowers.

SALT-MARSH CORDGRASS

SALT-MARSH ZONES

Also called smooth cordgrass, this species is the dominant low-marsh plant throughout the Atlantic coast of North America. Stands of this grass grow to 7 ft (2 m) high.

The low marsh is the part flooded once or twice a day at high tide, while the high marsh is the area above the mean high-tide level—it is flooded only occasionally, by the highest spring tides. Each zone has distinctive vegetation. pool

highest spring tide mean high tide upper high marsh mean sea level

lower high marsh

upland

high marsh

low marsh

mudflat

125

ALGAE-COVERED MUDFLATS

Some mudflats, such as these in Alaska, become heavily encrusted with green algae. The algae is often itself colonized by large numbers of tiny marine snails. HUMAN IMPACT

CONSERVING SALT MARSHES Salt marshes are threatened worldwide through being built on, converted to farmland, or even used as waste dumps. Over half of the original salt marshes in the US, for example, have been destroyed. This is regrettable, as salt marshes are valuable wildlife habitats and centers of biodiversity.

Animal Life Measured by the amount of organic matter (the base material for food chains) that they produce, salt marshes are extremely productive habitats. Most of this material comes from decaying plant material. When plants die, they are partially decomposed by bacteria and fungi, and the resulting detritus is consumed by animals such as worms, mussels, snails, crabs, shrimp, and amphipods living in the marsh, and zooplankton living in the salt water. These in turn provide food for larger animals. Salt marshes provide nursery areas for many species of fish, and feeding and nesting sites for birds such as egrets, herons, harriers, and terns. Tidal flats are home to many types of crustaceans, worms, and mollusks, which either feed on the surface or burrow beneath it. These in turn provide food for enormous numbers of wading birds.

A common inhabitant of salt marshes in the USA and parts of east Asia, the Great Egret, and closely related Eastern Great Egret, feeds on small fish, invertebrates, and small mice. MARSH HOUSING DEVELOPMENT

This coastal development in Myrtle Beach, South Carolina, has been built on top of a drained salt marsh. However, the adjoining area of marsh has been carefully preserved.

LUGWORM CASTS

Lugworms live in burrows some 8–16 in (20–40 cm) deep in tidal flats. They feed by taking in sand or mud, digesting any organic matter, and excreting the rest as a cast.

This toad, found in parts of western and northern Europe, inhabits upper salt marsh habitats (just below the high marsh), where it uses shallow ponds to breed.

OCEAN ENVIRONMENTS

GREAT EGRET

NATTERJACK TOAD

126

MARSH AT LOW TIDE

Patches of salt marsh surround the basin, together with tidal flats that can extend for up to 3 miles (5 km) from the shore at low tide.

ATLANTIC OCEAN NORTHWEST

Minas Basin TYPE Tidal sandflats and mudflats, and salt marshes

490 square miles (1,250 square km)

AREA

LOCATION Eastern part of Bay of Fundy, Nova Scotia, Canada

The Minas Basin is a semi-enclosed inlet of the Bay of Fundy. It consists of a triangular area of tidal mudflats and sandflats, surrounded by patches of salt marsh, most of which have been diked and drained for agriculture. Twice a day, the sea fills and empties the basin, rising and falling by over 40 ft (12 m), which is the largest tidal range in the world. No other coastal marine area has such a large proportion of its floor exposed at low

tide. Sediments in the basin, which are brought in and deposited by tides, range from coarse sand to fine silt and clay. The tidal flats formed by these sediments contain high densities of a marine amphipod, the Bay of Fundy mud-shrimp, which provides food for huge numbers of migrating shorebirds,

ATLANTIC OCEAN NORTHWEST

Cape Cod Salt Marshes TYPE

Salt marshes AREA

30 square miles (80 square km)

OCEAN ENVIRONMENTS

LOCATION

Cape Cod, eastern Massachusetts, US

Salt marshes are the dominant type of coastal wetland around Cape Cod, although about a third of the region’s marshes have been lost or severely degraded within the past 100 years. These salt marshes occur behind barrier beaches or spits and within estuarine systems, and have developed over the past 3,000 years in response to sea-level rise. They mainly RACE POINT

A typical area of salt marsh can be seen here behind dunes at Race Point, at the northern extreme of Cape Cod.

including sandpipers and plovers. The numbers peak from July to October, and for some species exceed 1 percent of the world population. SEMIPALMATED SANDPIPER

Half a million semipalmated sandpipers stop off in the Minas Basin each year on their way from North America’s Arctic regions to South America.

consist of high marsh, where the dominant plant species is saltmeadow cordgrass, with some scattered areas of low intertidal marsh, dominated by smooth cordgrass. The low marsh areas are flooded twice daily and the high marsh twice a month, during the highest spring tides. The largest individual marsh is the Great Salt Marsh to the west of the town of Barnstable. With deep channels running through it, this is a popular area to explore by kayak. The marshes around Cape Cod serve as a breeding and foraging habitat for a diversity of brackish and freshwater animals. Among these are two rare and protected bird species, the northern harrier and least tern, and two endangered reptiles, the diamond-backed terrapin and eastern box turtle. Restoring degraded salt marshes on Cape Cod is regarded as a top priority for many regional and national conservation organizations. Restoration will allow these wetlands to regain their function as a barrier protecting the coastline from storm surges and as a natural sponge that filters pollutants and excess nutrients from the water runoff in the region.

127 ATLANTIC OCEAN NORTHWEST

South Carolina Low Country TYPE

Salt marshes and tidal mudflats AREA

630 square miles (1,600 square km) South Carolina coast, southwest and northeast of Charleston, US

LOCATION

The Low Country contains one of the most extensive systems of salt marsh and tidal flats in the United States. Its size results from the broad, gently sloping, sandy coast of the US eastern seaboard, coupled with a moderately high tidal range of 5–7 ft (1.5–2 m).

Each day, two high tides inundate a vast area of the coastal zone, maintaining a system of channels, creeks, and rivers. The influence of both fresh and salt water here results in some diverse ecological communities. Smooth cordgrass is the dominant grass in the lower marshes, where the ground stays wet and muddy as a result of the tides. From late spring to fall, darker dead-looking sections of a grass called needle rush can also be seen. These two grasses are replaced toward higher ground by sea oxeye and the similar but taller marsh elder. In the lower marshes and the bordering tidal flats, mud snails, crabs, shrimp, worms, and other tiny inhabitants burrow into the mud, while attached and clinging to the stalks of the grasses are ribbed mussels and marsh periwinkles. Among the fish living in the silty tidal wash are croaker, menhaden, and mullet. Birds living here include marsh wrens and clapper rails. CORDGRASS MEADOWS

A tidal channel weaves its way through stands of smooth cordgrass, the dominant plant species in the lower marsh areas.

ATLANTIC OCEAN NORTHEAST

Morecambe Bay Tidal mudflats and sandflats, and salt marshes

TYPE

120 square miles (310 square km)

AREA

LOCATION

Northwest England, UK

MORECAMBE MUDFLATS

The ebbing tide reveals half of the bay’s total area as undulating expanses of mud and sand, meandering channels, and tidal pools.

The edges of the Wadden Sea are a mosaic of marsh patches broken up by shallow tidal channels.

ATLANTIC OCEAN NORTHEAST

Wadden Sea TYPE Tidal mudflats and sandflats, salt marshes, and islands

4,000 square miles (10,000 square km)

AREA

North Sea coast from Esbjerg, Denmark, along northern Germany, to Den Helder, Netherlands

LOCATION

The Wadden Sea is an extensive body of shallow water and associated tidal flats, salt marshes, and low-lying islands in northwestern Europe. Straddling the shores of Denmark, Germany, and the

Netherlands, the Wadden Sea has been formed by storm surges and sea-level rise inundating an area of coast, combined with the deposition of fine silt by rivers. It is an important nursery for North Sea fish species such as plaice and common sole, and its extensive mudflats are home to a number of mollusks and worms. The salt marshes provide a habitat for more than 1,500 species of insects and are important feeding and breeding grounds for many species of birds. Unfortunately, these marshes are threatened by intensive farming, industrial development, and climate change. In 2009, parts of the region were declared a UNESCO World Heritage Site.

HUMAN IMPACT

COCKLING Morecambe Bay has many rich cockle beds. The cocklers use planks of wood called jumbos to soften the sand, which helps draw the cockles to the surface. Because of the fast-moving tides, cockling has to be carried out with an eye on safety. In February 2004, a total of 23 Chinese migrant workers drowned after being cut off by the tides.

OCEAN ENVIRONMENTS

Formed from the confluence of five estuaries, those of the Kent, Keer, Leven, Lune, and Wyre rivers, Morecambe Bay is the largest continuous area of tidal flats in the UK. Broad, shallow, and funnel-shaped, the bay has a large tidal range, of up to 35 ft (10.5 m). During periods of spring tides, the sea can ebb as far as 7 miles (12 km) back from the high-water mark. The flood tide comes up the bay faster than a person can run, and parts of the bay are also affected by quicksand, posing dangers for anyone who does not know the area well. The bay’s extensive mudflats support a rich and diverse range of invertebrate animals, including cockles and mussels, snails, shrimp, and lugworms, as well as one of the largest populations of shorebirds in the UK. The bay regularly hosts 170,000 wintering waders, with several species present in internationally significant numbers, including oystercatchers, curlews, dunlins, and knots. The tidal flats are surrounded by extensive salt marshes, which make up about 5 percent of the total salt marsh in

the UK and support a number of rare plants. Much of this marsh area is grazed by sheep and cattle. The bay is an important location for commercial fishing; the fish species most commonly caught include bass, cod, whitebait, and plaice. However, Morecambe Bay has not escaped the problems of pollution common to many coastal areas of northwestern Europe. Oil, chemicals, and plastic are among the more common pollutants of this ecosystem.

SALT-MARSH MOSAIC

128

COASTS AND THE SEASHORE ATLANTIC OCEAN NORTHEAST

The Wash TYPE

Salt marshes, tidal sandflats, and mudflats AREA

100 square miles (250 square km) LOCATION

Northeast of Peterborough, England, UK

comprise the largest single area of this habitat in Britain and are growing in extent. The main plant species making up these salt marshes, which are traditionally used as grazing lands by farmers, are cordgrass and glasswort in roughly equal amounts. The Wash is one of the most important sites in the UK for wild birds, its sheltered tidal flats providing a vast feeding ground for migrating birds, such as geese, ducks, and waders.

These come to spend the winter in the Wash in huge numbers, with an average total of about 300,000 birds, from as far away as Greenland and Siberia. In addition, the Wash is an important breeding area for common terns and a feeding area for marsh harriers. It has been declared a Special Protection Area (SPA) under EU law. In 2000, parts of the artificial coastal defenses on the western side of the Wash were deliberately breached

to increase the area of salt marsh in the region. This has taken pressure off other nearby sea defenses, because the newly establishing area of salt marsh soaks up wave energy, acting as a natural sea defense. This is a relatively novel approach to coastal management that employs “soft engineering” techniques to defend against the erosive power of the sea. It also has the added environmental advantage of providing additional habitat for wildlife.

The Wash is a large, square-mouthed, shallow estuary on the eastern coast of England, surrounded by extensive areas of tidal sandflats, some mudflats, and salt marshes. It is fed by four main rivers: the Great Ouse, Nene, Welland, and Witham. The sandflats of the Wash range from extensive fine sands to drying banks of coarse sand and are home to large communities of bivalve mollusks, crustaceans, and polychaete worms. The extensive salt marshes TERRINGTON MARSHES

Located close to the mouth of the Nene River, these marshes form part of the Wash National Nature Reserve.

HUMAN IMPACT

SALT HARVEST

EDGE OF THE MARSHES

OCEAN ENVIRONMENTS

The dominant plant species in the nonexploited areas of salt marsh, such as at La Turballe in the northern part of the marshes, include sea-blite, cordgrass, and glasswort. ATLANTIC OCEAN NORTHEAST

Guérande Salt Marshes TYPE Salt marshes, artificial salt pans, and tidal mudflats

7 square miles (50 square km)

AREA

LOCATION

Northwest of St. Nazaire, Atlantic coast

of France

The region of salt marshes close to the medieval town of Guérande is most famous for its salt production but is also a noted ecological site, important for its role as a feeding and resting site

for large numbers of birds. The salt marshes came to exist in their present state through a combination of geology, climatic factors, and human intervention. Around the coast near Guérande, a system of spits and coastal dunes developed thousands of years ago, cutting off an area of shallow water, which was nevertheless subject to tides—seawater could flow in through two inlets in the dune belts. Over the centuries, marshes and tidal flats developed in this basin. During the past 1,000 years or so, these have been artificially converted into a mosaic of salt pans, separated by clay walls, although some areas remain unexploited. During the flood tide, seawater is allowed to flow through

channels into the pans, and during the warm summer months, when the rate of evaporation is high, sea salt is skimmed from the surface of the pans by an army of salt-farmers (paludiers). The areas of marsh surrounding the salt pans are made up of various salt-tolerant plants. More than 70 different species of birds nest and breed in the area, and many species spend the winter here in large numbers. For many years, the salt-farmers and the French ornithological society, the LPO, have jointly organized exhibitions and guided tours in the Guérande Salt Marshes, which are themed on the economics of salt production, the ecology of the marshes, and their need for protection.

The Guérande region has had salt pans for over 1,000 years. Today, about 300 salt-farmers work in the area, one of the few places in France where salt continues to be produced in a traditional manual way. The average annual harvest is about 10,000 tons of natural, mineral-rich sea salt, which is sold unrefined, with nothing added and nothing removed. The salt has a light gray color because of its content of fine clay from the salt pans.

129 PACIFIC OCEAN NORTHWEST

PACIFIC OCEAN NORTHWEST

Saemangeum Wetlands

Yatsu-Higata Tidal Flat

TYPE

TYPE

Mudflats, sandflats, and salt marshes

Tidal mudflat AREA

AREA

1/6 square mile (0.4 square km)

155 square miles (400 square km) LOCATION

South of Seoul, on the west coast of South Korea

LOCATION

Situated at the confluence of the Mangyeung and Dongjin river estuaries, on South Korea’s Yellow Sea coast, the Saemangeum Wetlands is a shorebird staging site of great importance. Its tidal flats and shallows support many bird species, some of which are considered to be globally threatened. In 2010, the status of this

Yatsu-Higata is a tiny rectangular mudflat at the northern end of Tokyo Bay, and is unusual because it is almost completely surrounded by a dense urban area. Once open shoreline, Yatsu-Higata now sits 3/5 mile (1 km) inland. Twice daily, it experiences a tidal inflow and outflow of water from Tokyo Bay via two concrete channels. When the tide comes in, the mudflat fills with about 3 ft (1 m) of water. When it flows out, a variety of resident and migrant shorebirds congregate to feed on the lugworms, crabs, and other marine animals that live within the fine silt that remains. Yatsu-Higata is an important stopover point for migrating birds flying from Siberia to Australia and Southeast Asia.

SPOON-BILLED SANDPIPER

This extremely rare species is one of the shorebirds most threatened by the reclamation project.

PACIFIC OCEAN NORTHEAST

Alaskan Mudflats TYPE

Tidal mudflats AREA

4,000 square miles (10,000 square km)

Various coastal inlets of southern and western Alaska, US

LOCATION

Narashino City, at the northern part of Tokyo Bay, Japan

wetland—as well as the thousands of migratory birds that depend on it as a key feeding area— came under threat due to the completion of a 22-mile- (33-km-) long sea wall at the mouth of the two estuaries. The sea wall is part of a project to turn the Many areas on the coast of southern and western Alaska are fringed by mudflats that appear at low tide. They are formed of a finely ground silt that in some areas is several hundred yards deep. This silt has originated from the action of Alaska’s numerous glaciers, which have been grinding away at the surrounding mountains for thousands of years. As these glaciers melt, the silt is carried to the coast in meltwater and deposited as sediment

LOW TIDE AT DONGJIN ESTUARY

The area around the estuary consists of tidal flats and scattered salt marsh intersected by channels that fill at high tide.

wetland into dry land for industrial or agricultural use, together with a freshwater reservoir. The project is going ahead despite the fears of conservation groups that it will result in irreversible environmental damage. when it reaches the sea. Because tidal ranges around Alaska are generally high, the total area of mudflats exposed at low tide is huge. These mudflats are an important stopover for migrating shorebirds. Various species of burrowing worms and bivalve mollusks are an important source of food for these waders and for the waterfowl that feed on the mudflats through the winter. Harbor seals also use the mudflats as rest areas.

Brown bears are occasional visitors to some Alaskan mudflats, where they dig for Pacific razor clams buried in the mud. They probably find the clams by looking for the small holes they leave on the surface as they burrow down. Extracting them is tricky, since when disturbed, they burrow down further. ALASKAN BROWN BEAR

This large adult bear is digging on the coast of Katmai National Park, at the eastern end of the Alaskan Peninsula.

DRYING MUDFLATS

These mudflats are at the edge of a large delta on the southwest coast of Alaska, formed by the Yukon and Kuskokwim rivers.

OCEAN ENVIRONMENTS

DIGGING FOR CLAMS

The mudflats are dangerous for human visitors, because in some areas they behave like quicksand. Even mud that at first seems firm enough to support a person may in reality be treacherous. A number of people have become stuck and some have even drowned.

130

COASTS AND THE SEASHORE

Mangrove Swamps A MANGROVE SWAMP IS A COLLECTION

of salt-tolerant evergreen trees, thriving in an intertidal environment in the tropics or subtropics. Mangrove swamps line about eight percent of the world’s coastlines, where they filter pollutants AERIAL ROOTS from river runoff and help prevent the silting up of adjacent Many mangrove species have aerial roots. These marine habitats. They also protect coastlines against erosion and prop the tree up and take in oxygen, which is provide a home for fish, invertebrates, and many other animals.

Formation

AT L A

N T

IC O C

Mangrove swamps develop in coastal areas protected from direct wave action. These areas often fringe estuaries and coastal lagoons (see p. 114). Most mangroves develop in fine muds or sandy sediments that form in these environments. As the lower parts of the mangrove roots develop in the sediment, aerial roots form a tangled network above it. This traps silt and other DISTRIBUTION Mangrove swamps occur only material carried there by rivers and tides. between latitudes 32˚N and 38˚S. PA C I F I C Land is built up, and then colonized by Salt marshes and tidal flats (see OCEAN p.124) replace them elsewhere. other types of vegetation.

usually not available in the mud that most mangroves grow in.

EAN

INDIAN OCEAN

OCEAN ENVIRONMENTS

ERN OCEAN SOUTH

Plants Some 54 species of trees and shrubs are classified as “true” mangroves, occurring only in mangrove habitats. Each has evolved special adaptations to the conditions they grow in, such as salty water. For example, some mangroves can excrete salt in their leaves. On most mangrove shorelines, there are two or three zones, each dominated by different mangrove species. In the Americas, just four main species are found. The area closest to the sea is dominated by red mangroves. Landward of this are black mangroves—the roots of this and some PNEUMATOPHORES other species develop pencil-like breathing These vertical tubes grow tubes, called pneumatophores. White and up out of the sand or mud button mangroves grow farther landward. The as extensions of horizontal mangrove swamps on the coasts of the rest of roots. When exposed to the tropics contain greater species richness. the air, they take in oxygen.

RED MANGROVE

This mangrove species can grow in deep water by means of its numerous prop roots, which often have a reddish tint. It also has a particularly high salt tolerance.

131

Animal Life

BANDED ARCHERFISH

Mangrove swamps are rich centers of biodiversity. Mangrove trees produce enormous amounts of leaf litter, as well as twigs and bits of bark, which drop into the water. Some of this immediately becomes food for animals such as crabs, but most is broken down by bacteria and fungi, which turn it into food for fish and shrimp. These in turn produce waste, which, along with the even smaller mangrove litter, is consumed by mollusks, amphipods, marine worms, small crustaceans, and brittlestars. Some of these become food for larger fish, and the various fish species provide food for larger animals. Across the world, mangrove swamps are home to an enormous number and MANGROVE diversity of birds and several endangered BRITTLESTAR This scavenger is one species of crocodiles. Other types of of the few echinoderms animals found in great numbers and found in mangrove diversity in mangrove swamps include swamps. It is highly frogs, snakes, insects, and mammals mobile, using its long ranging from swamp rats to tigers. arms to pull itself along.

This little fish inhabits mangrove swamps in the Indian and Pacific oceans. It is known as an archer- fish because it feeds mainly on flying insects, which it knocks out of the air and into the water by spitting at them.

JABIRU STORK

This large stork inhabits mangrove swamps and other wetlands throughout the tropical Americas, feeding on a range of prey, including snakes.

SHRIMP FARMING

SHELTER FROM PREDATORS

Cardinalfish, sheltering here in a mangrove swamp in Papua New Guinea, are one of the many types of small tropical fish that use mangrove roots for protection from predators.

About a quarter of the world’s mangrove swamps have been destroyed since 1980 and have been built on or turned into commercial enterprises such as shrimp farms (including the one shown here, in Vietnam). Unfortunately, intensive shrimp farming often has devastating environmental effects. Typically, the effluent from shrimp ponds pollutes nearby coastal waters, destroying more mangroves as well as coral reefs along the coastline.

OCEAN ENVIRONMENTS

HUMAN IMPACT

132

MANGROVE-LINED CHANNEL

Here, parallel stands of red mangrove line a shallow offshoot channel of Florida Bay in the southern part of the Everglades National Park.

ATLANTIC OCEAN WEST

Everglades PRINCIPAL SPECIES

Red, black, and white Mangroves Mangroves only: 600 square miles (1,500 square km)

AREA

LOCATION

Southwestern Florida, US

Mangroves occupy a large, roughly triangular area at the southwestern tip of southern Florida, where a maze of islands along the coast is intersected by mangrove-lined channels. Here, where the salt water of the Gulf of Mexico and Florida Bay meets fresh water that has traveled from Lake Okeechobee in central Florida, is the largest area of mangrove swamps in North America.

ATLANTIC OCEAN WEST

ATLANTIC OCEAN WEST

Alvarado Mangrove Coast

Sian Ka’an Biosphere Reserve

PRINCIPAL SPECIES

PRINCIPAL SPECIES

Red, white, and black mangroves

Red, black, white, and button Mangroves AREA

200 square miles (500 square km)

OCEAN ENVIRONMENTS

AREA

400 square miles (1,000 square km)

LOCATION To the southwest of Veracruz, Mexico, on southwestern Gulf of Mexico

LOCATION

The Alvarado Mangroves Ecoregion in southern Mexico is an extensive area of mangrove swamps mixed in with other habitats such as reed beds and palm forests. The mangroves grow on flat coastal land interspersed with brackish lagoons fed by several small rivers. The swamps are brimming with life, from rays gliding in the calm waters to snails climbing the mangrove roots, whose tangled network protects many fish and invertebrates from predators. Bird life in and around the swamps includes the keel-billed toucan, reddish egret, wood stork, and several species of herons and kingfishers, while the mammalian inhabitants include spider monkeys and West Indian manatees. Some large areas of mangroves in the region have been destroyed, and those that remain are under pressure from logging, agricultural expansion, oil extraction, and frequent oil spills.

Stretching for 75 miles (120 km) along Mexico’s Caribbean coast, the Sian Ka’an Biosphere Reserve contains a mixture of mangrove swamps, lagoons,

Eastern coast of Yucatán Peninsula, eastern Mexico, 90 miles (150 km) south of Cancún

ANHINGA

This diving bird hunts fish, frogs, and baby alligators in the Everglades mangroves.

The dominant species along the edges of the sea and the numerous channels is the red mangrove—water within the channels is normally stained brown from tannin contained in the leaves of this species. In addition to their role in stabilizing shorelines with and freshwater marshes; it was declared a World Heritage Site by UNESCO in 1987. The mangroves are protected from the energy of the Caribbean Sea by a barrier reef growing along the coast. However, the reserve’s terrestrial part is between 20 and 75 percent flooded, depending on season. Sian Ka’an’s mangrove systems are some of the most biologically productive in the world and their health is critical for the survival of many species in the western Caribbean region. Hidden between the massive mangrove roots live oysters, sponges, sea squirts, sea anemones, hydroids, and crustaceans. Bird species found here include roseate spoonbills, pelicans, greater

their large prop roots, red mangroves are crucial to the Everglades ecosystem, acting as a nursery for many species of fish, as well as shrimp, mussels, sponges, crabs, and other invertebrates. The other principal mangrove species in the Everglades are the black mangrove and white mangrove. Both of these grow closer to the shore than red mangroves, so they are in contact with seawater only at high tide. The Everglades swamps provide a feeding flamingos, jabiru storks, and 15 species of heron. The swamps are also home to West Indian manatees and two endangered crocodiles: the American crocodile and Morelet’s crocodile. The explosion of tourism in the nearby resort of Cancún poses several threats to the area. Unregulated development has increased pollution and altered the distribution and use of water in Sian Ka’an, compromising the health of the mangroves. BOAT TOUR

Because a large part of Sian Ka’an is flooded for much of the year, there are few roads into the area, so much of it can be reached and explored only by boat.

133

CICHLID INVASION

and nesting site for several mammals, including swamp rats, and numerous bird species, such as herons, egrets, gallinules, anhingas, and brown pelicans. While much of the region has an abundant alligator population, the swamps are the sole remaining stronghold in the US for the rare and endangered American crocodile. Also occasionally spotted in the channels between the mangroves are West Indian manatees (sea cows).

The Florida mangroves are sometimes damaged by the hurricanes that hit the region, hurricanes Katrina and Wilma in 2005 being examples. Hurricanes damage mangroves in two ways: strong winds may defoliate them, and storm surges harm them by depositing large quantities of silt on their roots. Fortunately, mangrove forests are resilient ecosystems, and they usually regenerate fully from hurricane damage within a few years.

Since 1983, the Mayan cichlid, an exotic fish species from Central America, has been spreading rapidly through the mangrove swamps and other wetland areas of the Everglades. No one yet knows what effect it may have on the region’s ecosystem. There are worries that it may displace native fish species; alternatively, it could be occupying a new “niche” that no other fish species has filled.

ATLANTIC OCEAN WEST

Belize Coast Mangroves PRINCIPAL SPECIES

Red, black, white, and button mangroves AREA

600 square miles (1,500 square km) Eastern Belize, on the western margins of the Caribbean Sea

LOCATION

rivers and trapping sediment, the mangroves also protect the clarity of the coastal waters, helping the coral reef to survive. Numerous cays—small islands composed largely of coral or sand—along the coast are covered with mangroves and form a habitat for birds. In all, more than 250 bird species share the swamps with West Indian manatees and a variety of reptiles, including boa constrictors, American crocodiles, and iguanas. MANGROVE ROOTS

ATLANTIC OCEAN WEST

Zapata Swamp PRINCIPAL SPECIES

AREA

1,500 square miles (4,000 square km) Western Cuba, 100 miles (160 km) southeast of Havana

LOCATION

The Zapata Swamp is a mosaic of mangrove swamps and freshwater and saltwater marshes that form the largest and best-preserved wetland in the Caribbean. The swamp was designated a Biosphere Reserve in 1999 and forms a vital preserve for Cuban wildlife, a spawning area for commercially valuable fish, and a crucial wintering territory for millions of migratory birds from North America. More than

Large numbers of these colorful birds live in the swamp, feeding off algae, shrimp, mollusks, and insect larvae that inhabit the mud at the bottom of the shallow waters.

900 plant species have been recognized in the swamp, and all but three of the 25 bird species endemic to Cuba breed there. All together, about 170 bird species have been identified in the swamp, including the common black-hawk, the greater flamingo, and the world’s smallest bird, the bee hummingbird. It also contains the remaining few thousand Cuban crocodiles. Mammalian residents include the Cuban hutia, a gopherlike rodent, and the West Indian manatee. The manjuari, or Cuban gar, is an unusual fish found only in the swamp. Adjacent to the swamp is the Bay of Pigs, where millions of land crabs breed each spring.

The mangrove swamps here are a nursery ground for many fish species associated with the huge Belize Barrier Reef. By filtering runoff from

A tangled maze of mangrove roots extends beneath the water’s surface all along this coast, providing refuge for a variety of juvenile fish.

OCEAN ENVIRONMENTS

Red, black, white, and button mangroves

GREATER FLAMINGOS

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COASTS AND THE SEASHORE INDIAN OCEAN WEST

Madagascar Mangroves PRINCIPAL SPECIES Gray, yellow, long-fruited stilt, and large-leafed orange mangroves

1,300 square miles (3,300 square km)

AREA

Scattered areas around the coast of Madagascar, off the eastern coast of Africa LOCATION

INDIAN OCEAN NORTH

Pichavaram Mangrove Wetland

Mangroves occur in a wide range of environmental conditions on Madagascar, fostered by a high tidal range, extensive low-lying coastal areas, and a constant supply of fresh river water, which brings a high silt load. They occupy about 600 miles (1,000 km) of the island’s coastline and are often associated with coral reefs, which protect them from ocean swell. The mangroves, in turn, capture river sediment that otherwise would threaten both reefs and seagrass beds. Up to nine different mangrove species

INDIAN OCEAN NORTH

Sundarbans Mangrove Forest

PRINCIPAL SPECIES Gray, milky, stilted, small-fruited orange, and yellow mangroves

PRINCIPAL SPECIES

5 square miles (12 square km)

AREA

Sundri, milky mangrove, yellow mangrove, Indian mangrove, keora 3,200 square miles (8,000 square km)

OCEAN ENVIRONMENTS

AREA

LOCATION Tamil Nadu, southeastern India, 90 miles (150 km) south of Chennai

LOCATION

Southwestern Bangladesh and northeastern India, between Calcutta and Chittagong

The Pichavaram Mangrove Wetland lies on a delta between the Vellar and Coleroon estuaries in southeastern India. It consists of a number of small and large mangrove-covered islets intersected by numerous channels and creeks. Fishing villages, croplands, and aquaculture ponds surround the area. This small, carefully preserved wetland is thought to have saved many lives during the 2004 Indian Ocean tsunami. When the tsunami struck, six villages that were physically protected by the mangroves incurred no damage, while other, unprotected villages were totally devastated. The wetland may have reduced the tsunami’s impact partly by slowing the onward rush of the sea through frictional effects and partly by absorbing water into its numerous canals and creeks.

This forest, a World Heritage Site since 1997, is the largest continuous mangrove ecosystem in the world. It is part of a

have been recorded in Madagascar, although only six are widespread. Several of Madagascar’s endemic birds, including the Madagascar heron, Madagascar teal, and Madagascar fish-eagle, use the mangroves and associated wetland habitats. Dugongs (relatives of manatees) glide through the waters, feeding on sea grasses, while huge quantities of invertebrates and fish swim freely among the fingerlike roots of the mangroves. These provide an abundance of food for animals such as the Nile crocodile,

sharks, and aquatic and wading birds, such as herons, spoonbills, and egrets. Many of the fish and bird species here are found nowhere else in the world. Unfortunately, the mangroves are threatened by urban development, overfishing, and the development of land for rice and shrimp farming. MANGROVE MAZE

This area of coastal mangroves, bisected by numerous channels, is located on the northeastern coast of Madagascar, at the mouth of the Ambodibonara River.

huge delta formed by sediments from the Ganges, Brahmaputra, and Meghna rivers.The region contains thousands of mangrove-covered islands intersected by an intricate network of waterways.The Bengal tiger swims here from island to island, hunting prey such as spotted deer and wild boar. Other inhabitants include fishing cats, rhesus macaque monkeys, water monitor lizards, hermit crabs, the Gangetic dolphin, and various sharks and rays. Habitat destruction threatens this region: more than half of the original mangroves have been cut down.

GAVIAL One extremely endangered inhabitant of the wetlands and rivers of Bangladesh is the gavial, a crocodilian. Once quite common in the Sundarbans, their numbers have dwindled due to accidental capture in fishing nets and other factors. Gavials are probably heading for regional extinction, although captive breeding programs in India and Nepal aim to save the species.

SATELLITE VIEW

In this satellite view of part of the Ganges– Brahmaputra–Meghna delta, the Sundarbans Mangroves form the area that appears dark red. On the right is the Bay of Bengal.

135 PACIFIC OCEAN WEST

Kinabatangan Mangroves PRINCIPAL SPECIES Stilt mangrove, long-fruited stilt mangrove, gray mangrove, nipa palm

400 square miles (1,000 square km)

AREA

LOCATION

Southeast of Sandakan, eastern Sabah,

Malaysia

Mangrove swamps occupy a coastal region of the Kinabatangan River delta, within eastern Sabah in the northern part of the island of Borneo. The mangrove swamps in this area form a complex mosaic with other types of lowland forest (including palm forest) and open reed marsh. They are home to dozens of species of saltwater fish, invertebrates such as shrimp and crabs, otters, and some 200 species of birds including various species of fish eagle, egret, kingfisher, and heron.

Irrawaddy dolphins are also occasionally spotted in the region, while other spectacular inhabitants include Borneo’s indigenous proboscis monkey and the saltwater crocodile (the world’s largest crocodile species), which was almost hunted to extinction but whose numbers are now recovering. Over the past 30 years, there has been extensive clearance of mangroves in the Kinabatangan delta for purposes of timber and charcoal production. The mangroves have either been replaced by oil palms or the cleared land has been developed for shrimp farming. Inevitably, the wildlife has suffered, but the government of Sabah is now engaged in a large-scale mangrove replanting operation. MANGROVE MONKEY

A female proboscis monkey, able to both swim and walk upright, is seen here with an infant, leaping across a waterway in the Kinabatangan mangroves. Her long tail helps to stabilize her movement through the air.

PACIFIC OCEAN EAST

Darien Mangroves

AERIAL ROOTS AT LOW TIDE

The mangroves are anchored in the soft mud by a dense network of roots that also provide a habitat for many animals.

PRINCIPAL SPECIES

Red, black, button, white, mora, and tea mangroves 360 square miles (900 square km)

AREA

Southeast of Panama City on the Pacific coast of eastern Panama

LOCATION

The Darien mangrove swamps lie around estuaries in eastern Panama in the Darien National Park, adjacent to the Gulf of Panama. Here, the roots of mangroves create a haven for mollusks, crustaceans, and many fish species. Shrimp are particularly abundant— the larvae hatch offshore, migrate to the mangrove “nursery” for a few months, and then return to sea as adults. Some of the mangrove swamps in this region have been converted to shrimp ponds or farmland. Other threats include urbanization and pollution. BLACK MANGROVE PACIFIC OCEAN WEST

New Guinea Mangroves

4,000 square miles (10,000 square km)

AREA

Scattered areas around the island of New Guinea in the western Pacific

LOCATION

Mangrove swamps occur in extensive stretches on New Guinea’s coastline. The longest and deepest stretches are found on the south side of the island, around the mouths of large rivers such as the Digul, Fly, and Kikori rivers. Mangrove communities here are the most diverse in the world—more than 30 different species of mangroves have

relatively low. Two endemic species of bats and a species of monitor lizard are found here. Ten bird species are endemic, including the New Guinea flightless rail, two species of lory, the Papuan swiftlet, red-breasted paradisekingfisher, and red-billed brush-turkey. Although largely intact, the mangrove regions in the western part of New Guinea have recently come under threat of pollution from the rapidly expanding oil and gas industries. SEAHORSE

This small seahorse is adopting the yellow color of fallen mangrove leaves.

These black mangroves are in the Punta Patiño Nature Reserve, a private reserve owned by a nonprofit environmental group.

OCEAN ENVIRONMENTS

PRINCIPAL SPECIES Gray, long-fruited stilt, tall-stilted, and cannonball mangroves

been found in a single swamp—and they form a vital habitat for a variety of animals living on the water’s edge. Underwater, over 200 different fish species, ranging from cardinal fish and mangrove jacks to seahorses and anchovies, have been recorded in either their adult or juvenile stages. Mudskippers (species of fish that can leave the water and climb trees), snails, and crabs climb the mangrove roots, while saltwater crocodiles patrol the channels between the mangrove stands. Although there are many species of fish and mangrove in these swamps, terrestrial animal diversity is

NEW GUINEA MANGROVES

This young saltwater crocodile is feeding among mangrove roots. Fully grown, this species is the largest of all crocodiles, growing up to 23 ft (7 m) long. Despite its name, it prefers fresh water, and adults compete fiercely for control of prime channels in swamps, often forcing juveniles into marginal rivers or out to the open sea.

THE SHALLOW SEAS that cover the

continental shelves around Earth’s landmasses nurture an extraordinary diversity of life. Energy from the Sun and nutrients from the land and sea ensure good conditions for plant growth, on which all marine life depends. The Moon is also a key player. Its gravitational pull drives the tides, which uncover the seashores each day, creating tidal currents that distribute plant nutrients and bring food to waiting animals. Each area of seabed provides a specific habitat for marine life that has adapted to the local conditions. The shallow seas comprise those parts of the oceans with which we are most familiar; yet we are only just beginning to understand the complexity of life there and its importance to the overall health of the planet.

SHALLOW SEAS CORAL REEFS

From polar seas to the tropics, the reflective surface of the sea hides a realm populated with unfamiliar life forms. Here in the tropics, animals look like plants, and plants hide inside the tissues of corals.

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SHALLOW SEAS

Continental Shelves CONTINENTAL SHELVES ARE ESSENTIALLY

the flooded edges of continents, inundated by sea-level rise after the last ice age. The shelf seabed is now approximately 600ft (200m) below the surface, and its width varies, occasionally extending to hundreds of miles. The shelf seabed and water quality are influenced by land processes. Rivers bring fresh water and nutrients, making shelf waters very productive ecologically, while river-borne material settles on the seabed as sediment. The continental shelf has a huge diversity of marine life and habitats, but it is also the area of the sea that suffers most from pollutants.

Fertile Fringes

SHALLOW SEAWEED

Seaweeds grow best on shallow, sunlit rocks, thrive in strong water movement, and provide food and shelter for many small animals.

The coastal fringes have the greatest diversity of life in the oceans. Light penetration is highly variable, from turbid basins to clear tropical waters. In many places, enough light reaches the shallow sea bed for good growth of photosynthetic organisms. Seaweeds, seagrasses, and phytoplankton thrive here, fed by solar energy, nutrients from land, and sediments stirred up by winds and currents. The coastal fringes are much more productive than the open oceans. Combined with diverse habitats, this results in complex marine communities, making rich feeding and nursery grounds for animals from deeper water. In higher latitudes, seasonal variations in the Sun’s strength stimulate an annual cycle of plankton and seaweed growth. In the tropics, where seasons are less pronounced, seagrasses and seaweeds grow year-round.

DISCOVERY

FIORDS Fiords are deep, sheltered sea inlets originally gouged out by glaciers and then flooded by the sea. They often extend many kilometres inland and are made up of deep basins, separated from the open sea by shallow sills. This basin-and-sill structure has a huge influence on marine life. In this sheltered environment, still, dark salt water lies beneath peaty fresh water. This mimics the marine conditions off the continental shelf, and animals normally confined to much deeper water, such as cold-water corals, inhabit water shallow enough for divers to explore.

Productive Plains Much of the continental shelf is covered with deep sediments. Sand, gravel, and pebbles are deposited in shallow water, while fine mud is carried into deeper water offshore. An important part of shelf sediments is biogenic (made from the remains of living organisms). It consists of carbonates (chemical compounds containing carbon) derived from, for example, coral skeletons, and microscopic plankton. At first sight, sediment plains appear barren. However, many different animals live hidden beneath the surface, either permanently or emerging from burrows and tubes to feed and reproduce. Shifting sand and gravel is a difficult place to live, but more stable sediments occur on deeper sea beds.Varying particle size makes it suitable for constructing burrows and tubes, and it can contain huge numbers of animals, providing a rich food source. These animal communities are all sustained by plankton falling from the continental-shelf surface waters, and by the products of decomposition of seagrasses and seaweeds.

SEDIMENT PREDATORS

Fish and starfish are top predators on sediments, eating the many different animals on the surface or buried beneath. Fish catch a wide range of creatures, while starfish capture slower-moving prey.

OCEAN ENVIRONMENTS

Shelf Fisheries The waters and sea bed of the continental shelf support most of the world’s major fisheries. In coastal waters, there is planktonic food for larvae and cover for juveniles, and this is where QUEEN SCALLOP 90 percent of the world’s total seawater Scallops feed by filtering seawater, catch reproduces. Demersal fish (living and can be collected by diving, or on or just above the seabed) such as cod farmed, with no damage to the and haddock feed on seabed life. Pelagic marine environment. (open water) shoaling fish such as sardines and herring feed on zooplankton, and are important food for larger fish such as mackerel and sharks, as well as for cetaceans and seabirds. Commercially important invertebrates such as shrimp are caught in shelf waters. Worldwide, JUVENILE SHELTER coastal communities are sustained by These baby cod are feeding small-scale, inshore fisheries, which in horse mussel beds, before moving offshore as adults. catch a wide range of marine life.

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SHELF DEPOSITS

The Mississippi River flows into the sea through a network of channels. As its silt-laden waters reach the sea, sediments fall out along the continental shelf.

Geology of the Continental Shelf

COASTAL POLLUTION For many years, coastal seas have been used as a convenient dump for human waste. Even the most remote seashores are now littered with plastic. More insidious is invisible pollution: nutrients and pathogens from sewage; heavy metals, organohalogens, and other toxins from industrial and agricultural effluents; radioactive waste from power stations; and hydrocarbons from effluents, oil spills, and other sources.

DREDGED TREASURE

Metals such as gold, tin, rare earth elements, and aggregates for the building industry are extracted by dredging continental shelves.

OCEAN ENVIRONMENTS

HUMAN IMPACT

Shelf deposits can be extremely thick. For example, those off eastern North America are up to 9 miles (15km) deep, and have been accumulating and compacting for millions of years. A cross-section here reveals ancient sediments other than those deposited by rivers and glaciers, including carbonates, evaporites, and volcanic materials. Carbonates are largely produced by marine life in shallow tropical seas. Evaporites are salts resulting from seawater evaporation in shallow basins or on arid coastlines. Evaporite deposits create domes in overlying sedimentary rocks, trapping oil and gas.

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SHALLOW SEAS

Rocky Seabeds

ROCKY SLOPE

FROM THE WARM TROPICS TO COLD POLAR SEAS, many

distinctive communities of marine life develop on the rocky floors of shallow seas. Underwater rocks provide points of attachment for both seaweeds and marine animals and are often covered with life. Seaweeds thrive in the sunlit shallows and provide a sheltered environment for animal communities. Firmly attached animals extend arms and tentacles to catch planktonic food from water currents, or pump water through their bodies to filter out nutrients. Mobile animals graze seaweeds or prey on fixed animals or each other. The life on a rocky reef depends on many environmental factors.

These underwater rocks in British Columbia, Canada, are covered with marine life. A sunstar and leather star search for prey among pink soft corals and sponges, while urchins graze below.

The Seaweed Zone Seaweeds rely on sunlight for growth, and thrive only on the shallowest rocks. The depth in which they can grow depends on water clarity, from a few yards in turbid seas, to more than 330 ft (100 m) in the clearest waters. In colder waters, huge forests of kelp and other large brown seaweeds dominate the shallows, with smaller seaweeds in deeper water. Large seaweeds are often scarce on rocks in the tropics—instead, the Sun’s energy is harnessed by tiny unicellular algae inside coral tissues. Seaweeds harbor a plethora of associated animals. Some live permanently in the seaweed zone, while others use it as a breeding ground or nursery before moving into deeper water. BALLAN WRASSE FOOD SOURCE

Energy from sunlight captured by seaweeds is used by grazing animals. Here, green seaweeds cover rocks in Orkney, Scotland.

OCEAN ENVIRONMENTS

ROCK GRAZERS Sea urchins are highly successful marine invertebrates, well defended by sharp spines. They graze the seabed, eating virtually everything except hard-shelled animals and coralline seaweed crusts. They have a profound effect on seabed communities. If urchins are abundant, they can seriously reduce the diversity of life on the seabed, leaving urchin “barrens.” Conversely, where urchins are sparse, they can increase diversity, by clearing spaces for new life to settle.

In summer, adult ballan wrasses lay eggs in nests built of seaweed, secured in rock crevices. Young wrasses are often patterned, providing camouflage.

Animal-dominated Deeps In deeper water, light levels are too low for most seaweeds, although encrusting red seaweeds need little light and grow farther down. Much of the plantlike growth in deeper water actually consists of fixed animals, which are most abundant in places with strong tidal currents. For mobile animals living here, the seabed is a minefield of toxic substances, released by fixed animals to deter predators. Below 160 ft (50 m), water movement from waves is much less, and fragile animals such as sponges and sea fans can grow to a large size. Here, and in places more sheltered from water movement, a smothering layer of fine silt continually settles on the rock surfaces, restricting the animal life to forms that can hold themselves above the rock or can remove the silt. On the most heavily silted rocks, animals may grow only on vertical or overhanging surfaces. ROCKY-BOTTOM PREDATOR

Stonefish have a textured skin and irregular shape, making them difficult to spot. A huge mouth engulfs prey, while the dorsal spines contain venom that can be fatal.

protruding eye used when hiding in sediment

dorsal spines with poison glands camouflage skin color and texture

large mouth tail fin

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Vertical Rock Underwater cliffs are often more heavily colonized with invertebrates than gently sloping rocks. In shallow water exposed to strong waves, various mobile seabed animals, particularly grazing sea urchins and predatory starfish, find it harder to cling to vertical and overhanging surfaces, and are knocked off by waves in rough weather.Vertical walls receive less sunlight, and are harder places for seaweed spores to settle, so there is less competition from seaweeds here than on horizontal rock. At sheltered sites, upward-facing rock is often covered with silt, and has few animals, but vertical and overhanging rock, by contrast, is silt-free and may have abundant life. Ledges and crevices in underwater cliffs provide safe refuges for fish and crustaceans.

JEWEL ANEMONES

Multicolored jewel anemones carpet vertical, wave-exposed rocks, with tentacles outstretched to catch food from the currents.

Crevices and Caves Irregularities in underwater rock features can provide additional habitats for marine life. Crevices and small caves provide shelter for nocturnal fish that hide during the day and are active at night. Elongated fish are well shaped to live in crevices, while fish that are active by day need holes to hide in at night and when predators approach. Deep, dead-ended caves contain a range of habitats, from sunlit, wave-exposed entrances to dark, still inner waters and sheltered sediments. Shrimp and squat lobsters occupy cave ledges, while animals that actively pump water to feed live in the quiet water inside the cave and coat the walls. Flashlight fish hiding in caves during the day signal to each other with light produced by bacteria in organs beneath their eyes. Small crevices are important because they form a refuge for small animals from sea urchins. TAKING REFUGE

The flattened body of this spiny squat lobster enables it to retreat far into narrow crevices if threatened, and the spines help to wedge it in small spaces.

Storms and Scour

CORALLINE ALGAE

Like a coating of hard pink paint, encrusting coralline algae can withstand considerable scouring from nearby sand and pebbles.

OCEAN ENVIRONMENTS

Shallow rocky reefs take the full force of waves during storms, but rock-living animals and seaweeds on open, exposed coasts are firmly attached and are generally well-adapted to cope with pounding waves. Larger seaweeds and animals will be torn from shallower rocks, KEELWORMS making space for new life to settle, while many Keelworms have a hard, seaweeds and colonial animals can regrow from calcareous shell that protects holdfasts or basal parts. However, few animals or their bodies from sand scour. plants survive on rolling boulders or on bedrock scoured by nearby sand and pebbles. Where rock meets sand, there is often a band of bare, sandblasted rock. Just above, tough-shelled animals such as keelworms survive, together with patches of hard encrusting calcareous red seaweeds. Above this, fast-growing colonial animals such as sponges and barnacles can colonize in the intervals between storms.

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SHALLOW SEAS

Sandy Sea Beds MOST OF THE CONTINENTAL SHELF

is covered with thick sediments, accumulated from millennia of land and coast erosion. The calcareous remains of marine life are continually added to the mix. Unlike deep-sea sediments (see pp.180-81), shelf sediments are stirred up by waves during storms, resuspending nutrients and profoundly affecting marine life and productivity. Sediments are largely the domain of animals, as seagrasses and seaweeds grow only in limited, shallow areas. Buried beneath the surface of a sandy sea bed, there may be vast numbers of animals hiding from, or waiting for, prey.

Gravel and Sand

coarse bristles (chaetae) on sides

The coarsest sediments from coastal and land erosion are usually deposited inshore by rivers and glaciers as they enter the sea. Frequently shifted by waves and tides, clean, coarse sand and gravel make a difficult habitat; typical inhabitants include tough-shelled molluscs, sea cucumbers, burrowing urchins, and crabs. A wider range of organisms live in the more stable sand and gravel, where purple-pink beds of maerl can be found. This unattached, calcareous seaweed SANDY HABITAT is made up of coral-like nodules. The open structure of live A marine segmented maerl twiglets is ideal for sheltering tiny animals, newly settled worm, the Sea Mouse from the plankton, while the dead maerl gravel underneath supports lives in muddy sand. burrowing animals. Beds of seagrass and green seaweeds thrive in shallow sand, harbouring a wide range of life. Embedded shells and stones provide anchors for various seaweed species. Many fish have adapted to life on sandy sea beds, the most familiar being flatfish. Shallow-water anglerfish wave their fishing lures to tempt prey within striking distance of their huge mouths, while garden eels live permanently in sand burrows, partly emerging to eat plankton. Sand eels and cleaver wrasse dive into the sand to avoid predators. GRAVEL DWELLER

This Flame Shell lives in a nest of gravel, pebbles, and shells. It pumps seawater through the nest, extracting food with its sticky, acidic tentacles.

OCEAN ENVIRONMENTS

Soft Mud In sheltered waters in enclosed bays, estuaries, and fiords, and in the deeper parts of the continental shelf, the finest particles of sediment settle as soft mud. Easily stirred up, the fine particles smother newly settled larvae and clog gills. There is little oxygen just below the mud surface, so buried animals must find ways to obtain oxygen from seawater. Despite these challenges, mud can be very productive. Bacteria and diatoms are often abundant on the mud surface, providing food for hoovering animals such as echiuran worms. Stable burrows are more easily built in mud than in sand or gravel. Animals such as sea pens and burrowing anemones anchor themselves in the mud, raising sticky ANCHORED IN MUD polyps and tentacles This sea pen’s branches to catch the raining are covered with small plankton or to ensnare a polyps that feed on the plankton. passing fish or crustacean.

felt-like dorsal chaetae

EXPLOITING SANDY BEDS

Stingrays are among the many animals that hide in the sand of the sea bed; this Southern Stingray does so both to escape predators and to ambush prey.

Mixed Sediments Most sediments on the continental shelf are a mix of coarse and fine materials. An important part of these are calcareous fragments, derived from hard-shelled animals. Mixed sediments offer a wider range of building materials for tubes and burrows than sand or mud and are easier to traverse, so a far greater variety of animals live here. Seaweeds and hydroids cover the bed, attached to shells and pebbles.Visible life includes tube worms, brittlestars, and burrowing anemones; most of these withdraw into the sediment if threatened. Below the surface, hidden animals, including bivalves LIFE ON THE SEDIMENT and crustaceans, provide a rich Its mouth fringed by tentacles, source of food for animals that this half-buried sea cucumber (left) and a hermit crab inhabit can find and excavate it, such these mixed sediments. as starfish, crabs, and rays.

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SEA-BED STABILIZERS This sea bed owes its luxuriant growth, including hydroids, soft corals, and brittlestars, to the many Flame Shells and Horse Mussels hidden under the surface. These molluscs bind the shifting sediments with strong threads, creating a stable, complex surface that many other animals can colonize. Flame Shell nests join together to form extensive reefs, with holes for water exchange, so many other organisms can live inside and beneath the nests.

DISCOVERY

SEA WRECKS

Beneath the Surface

SEDENTARY HABIT

This Norway Lobster

lives in a U-shaped Wave-disturbed sand and gravel creates a mobile, with two well-oxygenated environment. Animals that live here, burrow exits and is mainly such as crustaceans, and echinoderms, move through nocturnal. the shifting sand without building permanent homes. Animals that disturb sediments in this way, or by ingesting and defaecating it, are called bioturbators and are important recyclers of nutrients. Less-disturbed sediments are inhabited by sediment stabilizers. These sedentary animals, many living in permanent burrows or tubes, can cope with oxygen depletion and being covered over. Some strengthen their burrows by lining them with substances such as mucus and draw in seawater to supply food and oxygen. Others filter seawater or hoover sediment by extending their siphons to the surface. Microscopic creatures (the meiofauna) live in between the sand grains.

OCEAN ENVIRONMENTS

The complex shape and hard surfaces of shipwrecks such as the one shown here (the Eagle, off Florida) attract sedentary invertebrates and fish. A new wreck may take some time to become colonized, depending on the material from which it is made. Small hydroids, barnacles, and keelworms often settle first, paving the way for other animals and seaweeds to grow on their hard shells. Filter feeders thrive in enhanced currents on the super-structure, while the spaces inside offer hiding places for fish and octopuses.

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SHALLOW SEAS

Seagrass Beds and Kelp Forests SEAGRASS BEDS AND KELP FORESTS

are very different habitats, but both are highly productive and contribute significantly to the total primary production of inshore waters. Seagrasses are the only fully marine flowering plants. They thrive in shallow, sunlit water on sheltered, sandy seabeds, primarily in warm water. Kelps are large brown seaweeds that grow as dense forests on rocks of the lower shore and subtidal zone, preferring cold water. Both of these ecosystems have a complex structure and provide shelter for a COLD-WATER KELP Kelps are large brown wide range of associated animals and seaweeds, seaweeds that live mainly in shallow subtidal zones. some of them found nowhere else.

Seagrass Beds

SEAGRASS MEADOWS

Seagrass meadows help to protect shallow sandy seabeds against erosion. NATURAL CAMOUFLAGE

This greater pipefish’s elongated shape and drab color make it hard to spot among seagrass leaves.

Seagrasses are the only flowering plants (angiosperms) that live entirely in the sea, and they grow best in shallow, sandy lagoons or enclosed bays, where the water clarity is good. They are also tolerant of variable salinity. Unlike seaweeds, seagrasses have roots, which they use to absorb nutrients from within the sediments, thus recycling nutrients that would otherwise be locked up below the surface. Their intertwined rhizomes and roots help to stabilize the sand, protecting against erosion and encouraging the buildup of sediments. The productivity and complex physical structure of seagrasses attract a considerable diversity of associated species, some of which are only found in seagrass beds. A variety of seaweeds and sedentary animals, including species of hydroids, bryozoans, and ascidians, grow on the leaves. Seagrasses are also a critically important food for animals such as manatees, dugongs, green turtles, and many aquatic birds.

OCEAN ENVIRONMENTS

Kelp Forests The term “kelp” was originally used to refer to the residue resulting from burning brown seaweeds, which was used in soap-making. It is now used more generally to refer to the many kinds of large brown seaweeds of the order Laminariales. Kelp forests grow best in colder waters, on shallow rocks with good water movement. The top DISTRIBUTION MAP Seagrass beds flourish in the edge of some kelp beds is visible at the lowest tides. tropics, while kelp forests Kelps grow densely on rock slopes down to around in cold, nutrient-rich 30–70 ft (10–20 m) deep, depending on water clarity. In thrive waters, extending into the deeper water, there is less light for photosynthesis and polar regions. kelps grow more sparsely; in most coastal waters they kelp forests cannot survive below 80 ft (25 m). In exceptionally seagrass beds clear water, kelps can grow at 160 ft (50 m). Many kelp species have gas-filled floats, which hold the fronds up to the light and away from grazers. Within the kelp forest, waves are subdued and many organisms live in its shelter. Although kelp habitats support rich marine communities, only about 10 percent of kelp is eaten directly by COASTAL DEFENSES animals; the rest enters A band of giant kelp can help to protect the food chain as coasts from severe detritus or dissolved storms by absorbing wave energy. organic matter.

HUMAN IMPACT

ENDANGERED GRAZERS Seagrasses are the primary food of green turtles, and the only food of manatees and dugongs. Globally, these animals are now endangered or vulnerable, threatened by the destruction of their feeding grounds. The coastal areas in which seagrass beds are found are often vulnerable to pollution. Runoff of nutrients and sediments from land affects water clarity, and is probably the biggest threat worldwide.

SEAGRASS BEDS AND KELP FORESTS

Kelp Communities

Nurseries and Refuges

Many kelps are treelike in shape, with a branched holdfast for attachment and a long stem (stipe), sometimes with floats, supporting a palmlike frond. This makes a kelp forest a multilayered environment in which different organisms live at different levels. Small spaces in the holdfast can KELP ANEMONE harbor hundreds of small animals from predators. This large anemone is unusually mobile, Some kelps have rough stipes covered with red and crawls or drifts up onto seaweed fronds to catch floating prey. seaweeds, although sea urchins and limpets may graze these in calm weather and in deeper water. Actively growing kelp fronds exude slime, which deters most animals from settling, but as growth slows later in the season, the fronds may become covered with a few species, particularly bryozoans, hydroids, and tube worms. These animals reduce the light reaching the fronds, and some kelps shed their fronds to get rid of unwanted settlers before growing new ones. The sea floor beneath the kelps may be covered with marine growth, or relatively barren if heavily grazed by sea urchins.

Seagrass beds and kelp forests are important refuges for young fish that need to hide from predators until they reach maturity. Many fish, such as the lumpsucker and swell shark, do not live among seagrasses or kelps as adults, but come into these habitats to spawn, giving their young a greater chance of survival. Small fish need small prey, and they find an abundance of food in the form of tiny worms, crustaceans, and mollusks among the seagrasses and in the sediment beneath, or in the undergrowth of kelp forests. These young fish are often unlike their parents, usually camouflaged in shades of green and brown to avoid detection. Some herbivorous fish from surrounding reefs come into seagrass beds only at night. Seagrass beds are important nurseries for some commercial invertebrates, including shrimp and cuttlefish.

BLUE-RAYED LIMPET

147

LUMPSUCKER

This baby lumpsucker is very vulnerable. However, it is well camouflaged on kelp fronds, to which it attaches itself with a sucker.

At the end of the growing season, these limpets move down into the holdfast to avoid being discarded with the old frond.

OCEAN ENVIRONMENTS

DENSE KELP FOREST Giant kelp is the world’s biggest seaweed. Its stipes can be more than 100 ft (30 m) long, and it can grow as fast as 20 in (50 cm) per day.

148

SHALLOW SEAS ATLANTIC OCEAN WEST

ATLANTIC OCEAN NORTHEAST

Laguna de Términos COASTAL TYPE

Sound of Barra

Shallow

COASTAL TYPE Island chain with sounds

lagoon WATER TYPE

Tropical

WATER TYPE

Cool

PRIMARY VEGETATION

PRIMARY VEGETATION

Seagrasses, seaweeds, and mangroves

Seagrasses, maerl, and kelp

LOCATION In the southwest of the Yucatán Peninsula, Campeche State, Mexico

Between South Uist, Eriskay, and Barra, Outer Hebrides, Scotland, UK

LOCATION

Strong tidal currents flow through the Sound of Barra, and its clear, shallow waters and sandy sea floor provide an ideal habitat for the eelgrass Zostera marina. The eelgrass beds, together with beds of maerl (see p.245), are home to many species of small animals. Such rich, current-swept communities in this part of Scotland are threatened by the building of rock causeways across the sounds, which cut off the nutrient-

bearing currents that are essential for healthy growth. Eelgrass also grows in nearby brackish lagoons, together with the tasselweed Ruppia maritima, which is regarded by some scientists as a type of seagrass. Forests of the kelp Laminaria hyperborea grow on rocks at the edges of the sound, and these are home to abundant sea squirts and sponges.

SATELLITE VIEW, WITH LAGOON AT TOP

Two channels connect this sedimentladen lagoon to the Gulf of Mexico, while three rivers feed in fresh water, producing a pronounced change in salinity. The seagrasses Thalassia testudinum, Syringodium filiforme, and Halodule wrightii cover 29 percent of the lagoon. With 448 recorded animal species, Términos is the most speciesrich of Mexico’s four large lagoons.

ATLANTIC OCEAN NORTHEAST

Falmouth Bay COASTAL TYPE

Rocky

with inlets WATER TYPE

Cool

PRIMARY VEGETATION

Laminaria hyperborea kelp, eelgrass LOCATION

Southwest Cornwall, England, UK

OCEAN ENVIRONMENTS

The coastline of Falmouth Bay includes two drowned river valleys (rias), the Fal and Helford, which are now long, sheltered sea inlets. Because of their rich marine life, these inlets,

EELGRASS STANDS

Healthy stands of eelgrass now thrive in the current-swept sound. Almost 90 per-cent of western Europe’s eelgrass was lost to a wasting disease in the 1930s.

together with part of Falmouth Bay, have been designated as a European marine Special Area of Conservation. Beds of the eelgrass Zostera marina and maerl (see p.245) in the inlets are home to a wide variety of animals, including the rare Couch’s goby. On the wave-exposed rocky coasts outside the inlets, the kelp Laminaria hyperborea grows in dense forests that support many associated seaweeds and animals.This kelp has a stiff stipe, which raises the frond off the sea bed and means that the forest has developed well vertically. On the rock beneath the kelp, there is competition for space among anemones, sponges, and smaller seaweeds, while other animals hide in kelp holdfasts. The kelp stipes have a rough surface and provide effective attachment points for red seaweeds, bryozoans, soft corals, and other types of encrusting animals. On the fronds, tiny blue-rayed limpets graze, and colorful sea slugs eat small hydroids and lacy bryozoans. In deeper water, the kelp Laminaria ochroleuca grows, close to its northern limit in Europe. This kelp is similar to Laminaria hyperborea, but has a smooth stipe on which little can grow. Two other kelps are found in the area, the sugar kelp (Laminaria saccharina), which has a crinkled frond, and furbelows (Saccorhiza polyschides), which has a large, hollow holdfast and grows up to 13 ft (4 m) long in just one season. CORNISH KELP FOREST

This forest of Laminaria hyperborea kelp has many different plants and animals living on the rocks beneath it, and on the kelp itself.

ATLANTIC OCEAN SOUTHEAST

Saldanha Bay Rocky and sandy bay with lagoon

SOUTH ATLANTIC KELP FOREST

On the west coast of South Africa, sea bamboo is the largest of the local kelps. It can grow as tall as 50 ft (15 m).

COAST TYPE

WATER TYPE

Cool

currents PRIMARY VEGETATION

Kelp and eelgrass LOCATION

Western Cape, South Africa

The cold Benguela Current flowing northward along the west coast of South Africa brings nutrient-rich water that is ideal for kelp growth, and sea bamboo (Ecklonia maxima)

is abundant in Saldhanha Bay. The smaller split-fan kelp (Laminaria pallida) becomes dominant in deeper water. South Africa is famous for its diversity of limpets, and the kelp limpet Cymbula compressa is found only on sea bamboo. Its shell fits neatly around the stipe, where it grazes. The highly endangered limpet Siphonaria compressa occurs only in the bay’s Langebaan Lagoon, grazing on the endemic eelgrass Zostera capensis.

SEAGRASS BEDS AND KELP FORESTS

149

INDIAN OCEAN WEST

Gazi Bay Shallow bay and fringing reef

COASTAL TYPE

WATER TYPE

Tropical

PRIMARY VEGETATION

Seagrasses and mangroves LOCATION

30 miles (50 km) south of Mombasa, Kenya

Gazi Bay’s shallow, subtidal mud and sand flats are sheltered by fringing coral reefs. Twelve species of seagrass grow on the mudflats, and these seagrass beds cover about half of the bay’s 6 square miles (15 square km). Mangrove-lined creeks flow into the bay, and this unusual proximity of mangrove, seagrass, and coral reef systems has led to scientific studies on how they interact. The seagrass beds proved to be important in trapping particles washed into the bay from the creeks. Most were trapped within 11/4 miles (2 km) of the mangroves. The seagrass beds provide food directly for shrimp larvae, zooplankton, shrimp, and oysters, and they are the main feeding grounds of all the fish in the bay, making them very important to the health of the local fisheries.

INDIAN OCEAN EAST

Lombok COASTAL TYPE

Semi-sheltered bays on rocky coast WATER TYPE

Tropical

PRIMARY VEGETATION

Seagrasses LOCATION

Lesser Sunda Islands, Indonesia

MANGROVES AND SEAGRASS

Unusually for mangrove-lined creeks, the water here is clear, and stands of seagrasses are able to flourish in the waterways leading into Gazi Bay.

At least 11,600 square miles (30,000 square km) of sea bed around Indonesia is covered by seagrasses. In the warm, shallow lagoons and bays, 12 species of seagrass flourish. Gerupuk Bay in the south of the island of Lombok contains 11 of the 12 Indonesian seagrass species, with Enhalus acoroides and Thalassodendron ciliatum forming dense stands. Analyses of the gut contents of fish that live among seagrass in Lombok’s waters

revealed that crustaceans were the dominant food source. However, a species of Tozeuma shrimp found there avoids the attention of predators by having an elongated body colored green with small white spots, a perfect camouflage against seagrass leaves. At low tide, local people use sharp iron stakes to dig for intertidal organisms, and this damages the seagrass leaves and roots, thereby threatening the survival of the beds.

HUMAN IMPACT

THREAT FROM TOURISM The islands of Southeast Asia contain the greatest diversity of seagrasses in the world, but human activity threatens them in many places. Tourism is a means of bringing a much-needed boost to many local economies and this necessitates the building of hotels and other tourist facilities in previously unspoiled areas.

Future tourist development in the region may threaten the Lombok seagrass beds as a result of pollution and loss of habitat through the building of beach facilities, such as marinas.

BAY OF PLENTY

The seagrass beds in Lombok’s bays are a source of seaweeds, sea urchins, sea cucumbers, mollusks, octopus, and milkfish for the area’s inhabitants.

OCEAN ENVIRONMENTS

HOTEL DEVELOPMENT

150

SHALLOW SEAS PACIFIC OCEAN WEST

Sea of Japan/East Sea COASTAL TYPE

Mainly rocky WATER TYPE

Warm to cold PRIMARY VEGETATION

Kelp and seagrasses Off the west coast of the island of Hokkaido, northern Japan LOCATION

The Sea of Japan/East Sea is influenced by the warm Tsushima Current from the south and the cold Liman Current from the north, so its marine flora is a rich mix of temperate and cold-water species because of the wide range of water temperatures in different parts of the coast. The mixing of these currents also provides plentiful nutrients for plant growth. Seagrass diversity is moderate, but eelgrasses are particularly well represented with

seven species, several of them endemic to the area. Kelps are also diverse, with species of Undaria, Laminaria, and Agarum thriving in the colder waters in the north. Kelp is highly nutritious, and Hokkaido is the traditional center of kelp harvesting. INVASIVE KELP

Since 1981, Asian kelp (Undaria pinnatifida) has spread from its indigenous sites in Japan, China, and Korea to four continents.

FEMALE RED PIGFISH IN KELP FOREST

PACIFIC OCEAN SOUTHWEST

Poor Knights Islands COASTAL TYPE

Offshore

islands WATER TYPE

Temperate

PRIMARY VEGETATION

Kelp and other brown seaweeds Off the east coast of Northland, North Island, New Zealand

LOCATION

In 1981, a marine reserve was set up around the Poor Knights Islands, extending 2,600 ft (800 m) out from the shore. The area is popular with divers for its caves and kelp forests. In the most exposed places, the kelp Lessonia variegata is predominant, while at more sheltered sites Ecklonia radiata is more abundant, together with the large brown seaweed Carpophyllum flexuosum. Large numbers of sea urchins dominate in some places.

PACIFIC OCEAN NORTHEAST

Izembek Lagoon Rocky coast and lagoon

COASTAL TYPE

WATER TYPE

Cold; low

salinity PRIMARY VEGETATION

Eelgrass and kelp On the northern side of the Alaskan Peninsula, Alaska, US

LOCATION

SEAGRASS BANKS

OCEAN ENVIRONMENTS

INDIAN OCEAN EAST

Shark Bay has one of the world’s largest seagrass beds, covering about 1,500 square miles (4,000 square km).

Shark Bay COASTAL TYPE Shallow, semi-enclosed bay

LOCATION

food for one of the world’s largest populations of dugongs (see p.419), which are preyed on by sharks. The adjacent Hamelin Pool is too salty for seagrasses, but it is well known for the growth of stromatolites (see p.232).

Shark Bay is a UNESCO World Heritage Site, and it contains one of the largest, most diverse seagrass beds in the world. Its 12 species of seagrass, which include Amphibolis antarctica and Posidonia australis, dominate the subtidal zone to depths of about 40 ft (12 m). The vast seagrass beds provide

POSIDONIA AUSTRALIS

WATER TYPE

Tropical;

high salinity PRIMARY VEGETATION

Seagrasses Inlet of the Indian Ocean, north of Perth, Western Australia

Izembek Lagoon covers 150 square miles (388 square km) of the Izembek State Game Refuge and is the site of one of the world’s largest eelgrass beds. The eelgrass Zostera marina grows in dense beds here, both subtidally and on intertidal flats, where it is grazed by wading birds at low tide. Over half a million geese, ducks, and shorebirds

stop over at the lagoon during migration to refuel on the eelgrass. On the rocky, open coasts outside the lagoon, kelp forests thrive in the cold water. The most common forestforming kelp here is bull kelp (Nereocystis luetkeana), which can grow to 130 ft (40 m) in length. Bull kelp is an annual, which means that it reaches maturity within a single year. It grows quickly, at a rate of up to 5 in (13 cm) per day. The huge fronds, which have many long, strap-shaped blades, are supported by gas-filled bladders (pneumatocysts) that are up to 6 in (15 cm) in diameter. FEEDING GROUNDS

After raising their young farther north, thousands of Brant geese graze on eelgrass in Izembek Lagoon in the fall before flying south to Baja California, Mexico.

151 PACIFIC OCEAN EAST

Monterey Bay Kelp Forest COASTAL TYPE

Rocky and sandy WATER TYPE

Cool to warm PRIMARY VEGETATION

Kelp LOCATION

South of San Francisco, California, US

The California coast is famous for its beds of giant kelp (Macrocystis pyrifera), the largest seaweed on the planet (see p.238). It forms dense forests just offshore, and in Monterey Bay it outcompetes bull kelp for sunlight in many places, but the latter dominates in more exposed areas. Inshore of these giant species, other smaller kelps thrive. The kelp forests provide a unique habitat. Sea otters (see p.402), which live among the kelp forests and eat sea urchins, are thought to be important in controlling the urchins, which graze on the kelp. Seagrasses of the genus Phyllospadix are also found in Monterey Bay. Unusually for seagrasses, they can attach to rock, and grow in the surf zone or in intertidal pools on rocky coasts. Each year over 140,000 tons of giant kelp are harvested in California for the extraction of alginates, which are used in the textile, food, and medical industries.

In exceptional circumstances, giant kelp can be 265 ft (80 m) long. The forests are at their thickest in late summer, and decline during the dark winter months.

OCEAN ENVIRONMENTS

SUNLIT FOREST

152

SHALLOW SEAS CORAL DIVERSITY

Coral Reefs

In this seascape off a Fijian island, groups of shoaling sea goldies hover over diverse species of coral, sponges, and other reef organisms.

CORAL REEFS ARE SOLID STRUCTURES

built from the remains of small marine organisms, principally a group of colony-forming animals called stony (or hard) corals. Reefs cover about 108,000 square miles (280,000 square km) of the world’s shallow marine areas, growing gradually as the organisms that form their living surfaces multiply, spread, and die, adding their limestone skeletons to the reef. Coral reefs are among the most complex and beautiful of Earth’s ecosystems, and are home to a fantastic variety of animals and other organisms; but they are also among the most heavily utilized and economically valuable. Today, the world’s reefs are under pressure from numerous threats to their health.

Types of Reefs Coral reefs fall into three main types: fringing reefs, barrier reefs, and atolls. The most common are fringing reefs. These occur adjacent to land, with little or no separation from the shore, and develop through upward growth of reef-forming corals on an area of continental shelf. Barrier reefs are broader and separated from land by a stretch of water, called a lagoon, that can be many miles wide and dozens of yards deep. Atolls are large, ring-shaped reefs, enclosing a central lagoon; most atolls are found well away from large landmasses, such as in the South Pacific. Parts of the reef structure in both atolls and barrier reefs often protrude above sea level as low-lying coral islands—these develop as wave action deposits coral fragments broken off from the reef itself. Two other types of reefs are patch reefs—small structures found within the lagoons of other reef types—and bank reefs, comprising various reef structures that have no obvious link to a coastline.

FRINGING REEF

BARRIER REEF

ATOLL

A fringing reef directly borders the shore of an island or large landmass, with no deep lagoon.

A barrier reef is separated from the coast by a lagoon. In this aerial view, the light blue area is the reef and the distant dark blue area is the lagoon.

An atoll is a ring of coral reefs or coral islands enclosing a central lagoon. It may be elliptical or irregular in shape.

OCEAN ENVIRONMENTS

coral grows on shoreline, forming fringing reef

island subsides when volcano has become inactive

sea level

BARRIER REEF

FRINGING REEF

lagoon volcanic island

ATOLL FORMATION

An atoll is shown here forming around a volcanic island. First, the island’s shore is colonized by corals forming a fringing reef (above). Over time, the island subsides, but coral growth continues, forming a barrier reef (above right). Finally, the island disappears, but the coral maintains growth, forming an atoll (right). Atolls can also form as a result of sea-level rise.

lagoon of shallow water

reef face ATOLL

coral continues to grow, forming barrier reef volcanic island becomes submerged central area filled by reef limestone coral continues to grow where waves bring food

CORAL REEFS

153

Reef Formation The individual animals that make up corals are called polyps. The polyps of the main group of reef-building corals, stony corals, secrete limestone, building on the substrate underneath. The polyps also form colonies that create community skeletons in a variety of shapes. An important contributor to the life of these corals is the presence within the polyps of tiny organisms called zooxanthellae, which provide much of the polyps’ nutritional needs. Other organisms that add their skeletal remains to the reef include mollusks and echinoderms. Grazing and boring organisms also contribute, by breaking coral skeletons into sand, which fills gaps in the developing reef. Algae and other encrusting organisms help bind the sand and coral fragments together. Most reefs do not grow continuously but experience spurts of growth interspersed with quieter periods, which are sometimes associated with recovery from storm damage. STONY CORAL

This group of branching hard corals is growing at a depth of about 16 ft (5 m) off the coast of eastern Indonesia. Individual stony corals can grow up to a few inches per year.

OPEN POLYPS

At the center of each polyp is an opening, the mouth, which leads to an internal gut. The tissue around the gut secretes limestone, which builds the reef.

Distribution of Reefs Stony corals can grow only in clear, sunlit, shallow water where the temperature is at least 64˚F (18˚C), and preferably 77–84˚F (25–29˚C). They grow best where the average salinity of the water is 36 ppt (parts per thousand) and there is little wave action or sedimentation from river runoff. These conditions occur only in some tropical and subtropical areas.The highest concentration of coral reefs is found in the Indo-Pacific region, which stretches from the Red Sea to the central Pacific. A smaller concentration of reefs occurs around the Caribbean Sea. In addition to warm-water reefs, awareness is growing about other corals that do not depend on sunlight, and form deep, cold-water reefs—some of them outside the tropics (see p.178). WARM-WATER REEF AREAS

The conditions needed for the growth of warm-water coral reefs are found mainly within tropical areas of the Indian, Pacific, and Atlantic oceans. The reefs are chiefly in the western parts of these oceans, where the waters are warmer than in the eastern areas.

COLD-WATER CORAL

This species, Lophelia pertusa, is one of a few of the reef-forming corals that grow in cold water, at depths to 1,650 ft (500 m).

HUMAN IMPACT

Bleaching refers to color loss in reef-building corals and occurs when the tiny organisms called zooxanthellae, which give corals their colors, are ejected from coral polyps or lose their pigment. In extreme cases, this can lead to the coral’s death.Various stresses can cause bleaching, including pollution, ocean temperature rise, and ocean acidification (see p.67). In recent decades, some mass bleaching events have affected reefs over wide areas.

OCEAN ENVIRONMENTS

CORAL BLEACHING

154

SHALLOW SEAS REEF CREST

Parts of a Reef

In front of the reef crest (the uppermost, seaward part of a reef), spurs of coral sometimes grow out into the sea, separated by grooves.

Distinct zones exist on coral reefs, each with characteristic levels of light intensity, wave action, and other parameters. Each zone’s characteristics determine the organisms that live there. The reef slope, or forereef, is the part that faces the sea. The upper parts of the reef slope are dominated by branching coral colonies and intermediate depths by massive forms. These are the areas of the reef with the greatest diversity of species. At the top of the reef slope is the reef crest. This takes the brunt of the wave action and is subject to high light levels. Shoreward of the reef crest is the reef flat, a shallow, relatively flat expanse of limestone, sand, and coral fragments that may become exposed at high tide. The number of corals decreases toward the shore. Barrier reefs and atolls have a final zone, the lagoon area.

sea urchin

crinoid

elkhorn coral staghorn coral maze coral

Species Diversity In addition to reef-building corals, the warm, sunny waters of a reef are populated by a huge variety of other animals as well as seaweeds. The richest and healthiest reefs are home to thousands of species of fish and other marine vertebrates, such as turtles, while all the major groups of invertebrate animals are also represented. These include sponges, worms, anemones, and non-reef-building corals (such as sea fans), crustaceans, mollusks (which include snails, clams, and octopuses), and echinoderms (sea urchins and relatives). Every nook and cranny of a reef is used by some animal as a hiding place and shelter. All the organisms in the reef are part of a complex web of relationships. Many organisms are also involved in mutualistic partnerships with other organisms, in which both species benefit. tube sponge

sea fan

star coral

QUEEN ANGEL FISH

OCEAN ENVIRONMENTS

One of hundreds of fish species found on the Caribbean reefs, this juvenile angelfish feeds on small crustaceans and algae.

lettuce coral

REEF ZONES

The structure of a typical fringing reef, including forereef, reef crest, and reef flat, and some of the sea life that inhabits it, are shown here. The forereef has three zones, which are dominated by different coral forms: branching coral, massive coral, and platy coral. Individual corals are not shown to scale.

platelike star coral finger coral sea whip

TUBE SPONGES

Different species of sponges are found in many parts of the reef, including caves and cavities, as well as on the open reef slope.

PLATY CORAL ZONE Corals in this deep, dark part of the forereef expand horizontally to capture maximum sunlight, forming platelike colonies.

CORAL REEFS

155

The Importance of Reefs beach small brain coral

SEA URCHIN

Sea urchins graze on algae and are important in preventing algal overgrowth on coral reefs.

seagrass

golf ball coral

sea anemone

Coral reefs are of inestimable value for many reasons. First, they provide a protective barrier around islands and coasts: without the reefs, these would erode away into the ocean. Second, reefs are highly productive, creating more living biomass than any other marine ecosystem and providing an important food source for many coastal peoples. Third, they support more species per square unit area than any other marine environment. In addition to known coral-reef species, scientists estimate that there may be several million undiscovered species of organisms living in and around coral reefs. This biodiversity may be vital in finding new medicines for the 21st century—many reef organisms contain biochemically potent substances that are being studied as possible cures for arthritis, cancer, and other diseases. Finally, because of their outstanding beauty, reefs contribute to local economies through tourism, particularly attracting snorkelers and scuba-diving enthusiasts (see p.474).

REEF FISHING

Small-scale fishing using hand nets, often transported to a suitable site by canoe, is common throughout the Indian and Pacific oceans, as shown here off Pantar Island in eastern Indonesia.

SAND AND ALGAL ZONE This area is dominated by sand and seagrass, which may harbor small marine life.

REEF FLAT The animals living here must be able to endure high temperatures and salinity.

REEF CREST The corals inhabiting this zone are invariably robust, as they must withstand energetic wave action.

HUMAN IMPACT

CORAL POISONING

GOLDEN CRINOID

Crinoids, or feather stars, are related to starfish. They usually live in a hole or other shelter on the reef, extending their elegant arms to catch food.

crinoid arm

Vulnerable Reefs BRANCHING CORAL ZONE This zone is just below the reef crest and is dominated by corals with branching forms, such as staghorn coral.

SUBMARINE STUDY

Here researchers record the frequency of algal species on a reef in the Hawaiian Islands, using a camera, a frame for delineating areas of reef, and underwater writing implements.

OCEAN ENVIRONMENTS

MASSIVE CORAL ZONE This central part of the forereef is usually dominated by massive corals—that is, colonies with rounded shapes.

Many types of stress can damage reefs and are doing so on a massive scale. Much of the harm is caused by human activity, including coastal pollution, uncontrolled development of coasts, and diving tourism. Other problems include collection of corals and reef organisms for the aquarium and jewelry trades, uncontrolled mining of reefs for building materials, and destructive fishing practices. Natural disturbances include tropical storms and mass die-offs of animals that help to maintain reef health. Coral bleaching, linked to rises in sea temperatures (see p.153), is particularly worrisome. Coral reefs can recover from periodic natural traumas, but if they are subjected to multiple sustained stresses, they perish. It has recently been estimated that two-thirds of the world’s warm-water reefs are at risk of disappearing in the near future.

One of the most destructive fishing practices, liable to kill corals over wide areas of reef, involves the use of poison to help catch tropical fish for the aquarium trade. This is practiced in parts of Southeast Asia such as the Philippines. The young boy photographed below, swimming at a depth of about 70 ft (20 m), carries a catch bag, net, and a squirt bottle containing a solution of sodium cyanide. The cyanide is used to immobilize selected reef fish, making them easier to catch, but kills all the living corals that it comes in contact with, taking a terrible toll on the health of the reef.

156

SHALLOW SEAS ATLANTIC OCEAN WEST

Bermuda Platform Atoll with fringing and patch reefs TYPE

150 square miles (370 square km)

AREA

CONDITION Some coral bleaching reported LOCATION Northwest Atlantic, extending west and north of the islands of Bermuda

The Bermuda Platform is the elliptical, flattened summit of a huge volcanic submarine mountain (seamount) in the northwest Atlantic. Its surface lies 13–60 ft (4–18 m) below sea level and is covered in a thick layer of limestone, formed over millions of years from the

ATLANTIC OCEAN WEST

Florida Reef Tract TYPE

Barrier reef, patch

reefs 400 square miles (1,000 square km)

AREA

BOILER REEFS

remains of corals and other organisms growing on the platform. Along the platform’s southern and eastern edges, limestone sand has gradually built up to form the Bermuda islands. Coral reefs are present around the other edges of the platform, forming an atoll, while patch reefs grow on its central surface. The diversity of reef flora and fauna here is less than that associated with the reefs in the Caribbean Sea to the south. over the past 35 years, mainly due to human impact. Live coral cover has decreased, coral diseases have become extensive, inhabitants that were once common (such as the queen conch) have virtually disappeared, and the area of reef encroached on by mats

LOCATION From east of Soldier Key, Biscayne Bay, to south of the Marquesas Keys, Florida, USA

This system of coral reefs is 160 miles (260 km) long and curves to the east and south of the Florida Keys. Some geologists classify it as a barrier reef, others as a barrier-like collection of bank reefs. It is the largest area of coral reefs in the US and has a high biodiversity, being home to more than 40 species of stony coral, 500 species of fish, and hundreds of mollusk species. The reefs’ health has declined

Bahama Banks TYPE Fringing reefs, patch reefs, barrier reef

1,200 square miles (3,150 square km)

AREA

CONDITION Localized areas of damage

OCEAN ENVIRONMENTS

LOCATION Bahamas, southeast of Florida, US, and northeast of Cuba

Lighthouse Reef TYPE

Atoll with patch

reefs

CONDITION Degraded; some recent recovery

ATLANTIC OCEAN WEST

ATLANTIC OCEAN WEST

These small reefs, close to the surface, are called “boilers” after their frothy appearance when waves break on them.

120 square miles (300 square km)

AREA

CONDITION

Western Caribbean, 60 miles (80 km) east of central Belize

LOCATION

Nevertheless, 21 different species of stony coral, 17 species of soft (non-reef-building) coral, including many spectacular purple sea fans, and about 120 different species of fish have been recorded here. of algae has expanded. Causes of this degradation include overfishing, fertilizer runoff from south Florida, increase in ocean temperature and sea level, and sewage pollution from boats. Other contributing factors include hurricane damage, declines in algae-grazing sea urchins, and direct damage from dive-boat anchors and ship groundings. Steps are being taken to reverse the decline, with some signs of success. CARYSFORT REEF

Carysfort Reef, part of the Florida Reef Tract, lies close to Key Largo and is the site of many ancient shipwrecks.

The Bahamas is an archipelago of some 700 islands scattered over two limestone platforms, the Little Bahama and Great Bahama Banks, in the West Indies. The platforms have been accumulating for at least 70 million years—the Great Bahama Bank is over 15,000 ft (4,500 m) thick—yet their surfaces remain 33–80 ft (10–25 m) below sea level. Many of the islands have fringing coral reefs; there are also many patch reefs on the Banks and a

Generally

healthy

barrier reef near the island of Andros. The reefs are home to a range of corals and coral reef-dwelling animals that is typical for the western tropical Atlantic. Although local declines in coral cover and occasional outbreaks of coral disease have been recorded, the reefs are generally healthy. There has been concern about overgrowth of algae, but for now the algae are being kept in check by a thriving population of parrotfish, which graze the reefs.

HARD AND SOFT CORALS

This diverse group of corals, including a large purple sea fan, was photographed off the island of New Providence.

Lighthouse Reef is an atoll lying 35 miles (55 km) east of the huge Belize barrier reef, off the coast of central Belize. It is roughly ovalshaped, about 23 miles (38 km) long, and 5 miles (8 km) wide on average.

CORAL REEFS Like all atolls, it is bounded by a ringlike outer structure of coral formations, many of which break the surface.These form a natural barrier against the sea and surround a lagoon, which sits on top of a mass of limestone.The lagoon is relatively deep but contains numerous patch reefs along with six small, sandy, low-lying islands, or cays (one containing a dive center). At its center is Lighthouse Reef ’s most remarkable feature—a large, almost circular sinkhole in the limestone, known as the Great Blue Hole. Approximately 410 ft (125 m) deep, this feature formed some 18,000 years ago during the last ice age, when much of Lighthouse Reef was above sea level. At that time, freshwater erosion

produced a complex of air-filled caves and tunnels in the limestone. At some point, the ceiling of one of the caves collapsed, producing what is now the entrance to the Blue Hole. Later, as sea level rose, the cave complex flooded, and it is now accessible only by adventurous scuba divers. Elsewhere, the atoll boasts large areas of mostly healthy reef, although some were affected by coral bleaching in 2010. As well as patch reefs within the atoll, around its margins are many coral-encrusted walls (dropoffs) that descend to depths of several hundred yards. Lighthouse Reef exhibits a biological diversity typical of the region; it is home to some 200 fish species and 60 species of stony corals.

157

HUMAN IMPACT

DIVING THE GREAT BLUE HOLE The Great Blue Hole is one of the world’s most exciting dive sites. It is not recommended for the fainthearted (as sharks are commonly encountered) or for novice divers (because perfect buoyancy control is needed). At 125 ft (38 m) depth, an array of impressive ancient stalactites can be seen hanging from the slanting walls of the hole. The entrance to a system of caves and tunnels lies a few yards farther down.

The water in this sinkhole extends to a depth of 410 ft (125 m), producing the deep blue color after which it is named.

OCEAN ENVIRONMENTS

GREAT BLUE HOLE

158

SHALLOW SEAS INDIAN OCEAN NORTHWEST

Red Sea Reefs TYPE Fringing, patch, and barrier reefs; atolls

6,300 square miles (16,500 square km)

AREA

CONDITION Localized areas of severe damage LOCATION Red Sea coasts of Egypt, Israel, Jordan, Saudi Arabia, Sudan, Eritrea, and Yemen

The Red Sea contains arguably the richest, most biologically diverse, and most spectacular coral reefs outside Southeast Asia. The coral reefs in the northern and southern areas of the sea differ considerably. In much of the northern section, the coasts shelve extremely steeply and there are few offshore islands. The coral reefs here are mainly narrow fringing reefs, with reef flats typically only a few yards wide, and slopes that plunge steeply toward the sea floor. In the south, off Eritrea and southwestern Saudi Arabia, is a much wider area of shallow continental shelf. Many of the reefs

INDIAN OCEAN NORTHWEST

Aldabra Atoll TYPE

Atoll

60 square miles (155 square km)

AREA

Excellent, although it has suffered some coral bleaching CONDITION

LOCATION Western extremity of the Republic of Seychelles archipelago, northwest of Madagascar

OCEAN ENVIRONMENTS

At 20 miles (34 km) long and 9 miles (14.5 km) wide, Aldabra is the largest raised coral atoll in the world. The term “raised” refers to the fact that the

in this area surround offshore islands, and there are fewer steep dropoffs. The southern Red Sea also receives a continuous inflow of water from the Gulf of Aden to its south that is high in nutrients and plankton, making the waters more cloudy, which restricts reef development. Live coral cover throughout the Red Sea reefs is generally high, at about 60–70 percent, as is the diversity of stony and soft corals, fish (including the famous Red Sea lionfish), and other reef organisms. More than 260 species of stony coral have been identified in the central Red Sea. Although many reef areas are healthy, others have been damaged by intensive diving tourism and deposition of untreated sewage. In 2010, a major coral bleaching event, linked to raised water temperatures, affected the central Red Sea. Coral predation by the crown-ofthorns starfish has also been a problem. GULF OF AQABA REEF

Groups of little red fish of the genus Anthias fluttering around hard coral heads, or colonies, are a familiar sight on Red Sea reefs.

limestone structures forming its rim, which originated from coral reefs, have grown into four islands that protrude as much as 27 ft (8 m) above sea level. Situated on top of an ancient volcanic pinnacle, the islands enclose a shallow lagoon, which partially empties and then fills again twice a day with the tides. Because of its remote location, and its status as a Special Nature Reserve and (since 1982) UNESCO World Heritage Site, Aldabra has escaped the worst of the stresses that human activities have placed on most of the world’s coral reefs. Although, in common with many Indian Ocean locations, the atoll was affected by

a severe coral bleaching event in 1997–98, its external reefs are in a near-pristine state. They are rich in marine life, featuring large schools of reef fish, green and hawksbill turtles, forests of yellow, pink, and purple sea-fans, groupers, hammerhead sharks, and barracuda. The atoll’s inner lagoon contains numerous healthy patch reefs, is fringed by mangrove swamps, and is inhabited by turtles, parrotfish, and eagle rays. On land, Aldabra is famous for its giant tortoises, rare exotic birds such as the flightless rail, and giant robber crabs, which have claws big enough to crack open coconuts.

INDIAN OCEAN WEST

Bazaruto Archipelago Fringing reefs, patch reefs

TYPE

60 square miles (150 square km)

AREA

Generally good; some damage

CONDITION

Southeastern coast of Mozambique, northeast of Maputo

LOCATION

The Bazaruto Archipelago is a chain of sparsely populated islands on the coast of Mozambique, formed where sand was deposited over hundreds of thousands of years by the Limpopo River. A Marine National Park, established in 2001, covers most of the archipelago, protecting its impressive fringing reefs and kaleidoscopic range of marine life. More than 2,000 fish species, 100 species of stony corals, and 27 dazzling soft-coral species, including unusual “green tree” corals, are found on Bazaruto’s reefs, as well as eagle rays, manta rays, and five species of turtles. The archipelago is also a refuge for one of the remaining populations of dugongs (see p.419) in the western Indian Ocean. REEF SAFARI

A peaceful way of visiting the shallow, crystal-clear waters around the Bazaruto reefs is on a dhow, as part of a reef safari.

MUSHROOM ROCK

Strong tidal flows of ocean water into and out of Aldabra’s lagoon have sculpted some raised clumps of old reef into mushroom-shaped islets known as champignons.

159 INDIAN OCEAN CENTRAL

Diego Garcia Atoll TYPE

INDIAN OCEAN CENTRAL

The numerous ringlike structures in this aerial view are faros—mini-atolls within a larger Maldivian atoll.

Maldives

Atoll

TYPE

Atolls, fringing

reefs

17 square miles (44 square km)

AREA

AREA 3,500 square miles (9,000 square km)

Generally good; recovered from coral bleaching in 1998

CONDITION

CONDITION Recovering from coral bleaching

LOCATION

Chagos Archipelago, central Indian Ocean, southwest of Sri Lanka

LOCATION

This atoll, best known as a US military base, is also home to one of the world’s largest populations of breeding sea birds. The reefs around the atoll’s edges and within its central lagoon are home to 220 species of stony coral. In 2010, the Chagos Archipelago, of which Diego Garcia forms a part, was declared a “no-take” marine reserve, making it the largest marine protected area in the world.

The Maldives are a group of 26 atolls, many of them very large, in the Indian Ocean. The majority are composed of numerous separate reefs and coralline islets (some 1,200 in all), arranged in ringlike structures. Within most of the atoll lagoons, which are 60–180 ft (18–55 m) in depth, there are usually many patch reefs and numerous structures called faros, which are rare outside the Maldives. These look like mini-atolls and consist of roughly elliptical reefs with a central lagoon. Most of the Maldivian atolls are themselves arranged in a large, elliptical ring, some 500 miles (800 km) long and 60 miles (100 km) wide. The reefs that fringe all the Maldivian atolls, islets, and faros contain more than 200 species of colorful stony coral, more than 1,000 different fish species, and are abundant in other marine life. Groupers, snappers, and sharks, for example, are frequently encountered. In 1998, a severe coral bleaching event killed up to 90 percent of the corals in some areas, and had a strong negative impact on diving tourism. Since 1998, a recovery has occurred, although another severe bleaching event took place in 2010.

WESTERN SIDE OF DIEGO GARCIA

ATOLLS WITHIN ATOLLS

Off southern India, southwest of Sri Lanka, in the Indian Ocean

HUMAN IMPACT

ATOLL CITY Male, the Maldives’ capital city, covers the entire surface area of a coral island that forms part of an atoll rim. Its reef has been mined to provide building materials for artificially extending the island.

INDIAN OCEAN NORTHEAST

Andaman Sea Reefs TYPE

Fringing reefs

2,000 square miles (5,000 square km)

AREA

CONDITION Some areas poor due to coral bleaching, diver damage

Andaman Sea coasts: Thailand, Myanmar, Andaman and Nicobar Islands, Malaysia, Sumatra

LOCATION

SOFT CORAL COLONIES

These soft corals and glass fish, which are almost transparent, were photographed off southwest Thailand.

and breeding grounds for endangered sea turtles. A coral bleaching event in 1998 badly damaged reefs around the Andaman and Nicobar islands, and in 2010 another severe widespread bleaching event affected the reefs along the coast of Thailand. The 2004 Indian Ocean tsunami caused relatively little damage. Other threats to these reefs include collection of marine life for aquariums, destructive fishing techniques, siltation caused by poorly managed deforestation on some of the islands, and anchor damage from dive boats.

OCEAN ENVIRONMENTS

Most Andaman Sea reefs are fringing reefs around islands off the coasts of Thailand and Myanmar or, in the northwest, off the eastern coasts of the Andaman and Nicobar islands—the site of the largest continuous area of reefs in south Asia. About 200 coral species and more than 500 fish species have been recorded here. The reefs and islands are also important feeding

The partly dismantled reef leaves the island poorly protected from storms, so a sea wall has been built around much of its perimeter, preventing major damage during the 2004 Indian Ocean tsunami.

160

SHALLOW SEAS PACIFIC OCEAN WEST

Shiraho Reef TYPE

Fringing reef

10 square km (4 square miles)

AREA

CONDITION Reasonable; damaged in parts by bleaching in 1998, 2007 LOCATION Southeast coast of Ishigaki Island, at the southwestern extremity of Japanese archipelago

Shiraho Reef, off Ishigaki Island, part of the Japanese archipelago, came to notice in the 1980s as an outstanding example of biodiversity, with some 120 species of coral and 300 fish

species concentrated in a few square kilometres. The reef also contains the world’s largest colony of rare Blue Ridge Coral (Heliopora coerulea). For decades, environmentalists battled to save the reef from the building of a new airport for Ishigaki. A proposal to construct the airport on top of the reef was dropped, but concern remains now that it has been built on land, as discharge of excavated soil into the reef is likely to have an adverse effect. BLUE RIDGE CORAL

Despite its name, the colour of this coral varies from violet through blue, turquoise, and green to yellow-brown. Its branching vertical plates can form massive colonies.

PACIFIC OCEAN WEST

Tubbataha Reefs TYPE

Atolls

330 square km (130 square miles)

AREA

CONDITION Good; recovering from coral bleaching in 2010

Central Sulu Sea, between the Philippines and northern Borneo

LOCATION

The Tubbataha Reefs lie around two atolls in the centre of the Sulu Sea and are famous for the many large pelagic (open ocean) marine animals attracted to them – such as sharks, Manta Rays, turtles, and barracuda. The steeply shelving reefs here are also rich in smaller life, including many species of crustaceans, colourful nudibranchs (sea slugs), and more than 350 species of stony and soft coral. In the early 1990s, the Tubbataha Reefs were rated by scuba divers among the top ten dive sites in the world. However, during the 1980s they suffered considerable damage from destructive fishing practices and the establishment of a seaweed farm.

In 1988, the Philippines government intervened, declaring the area a National Marine Park, and since 1993 it has also been a UNESCO World Heritage Site. The condition of the Tubbataha reefs has much improved, due to the enforcement of measures such as a prohibition on fishing and a ban on boats anchoring on the reefs (visiting craft must use mooring buoys). A setback occurred in January 2013 when a US Navy minesweeper ran aground on the reef, damaging over 2,000 square m (21,500 square ft).

CORAL DROP-OFF

In this photograph of a steeply shelving reef slope, several species of soft coral are visible, together with a shoal of Longfin Bannerfish.

PACIFIC OCEAN WEST

Nusa Tenggara TYPE Fringing reefs, barrier reefs

5,000 square km (2,000 square miles)

AREA

CONDITION Damaged by fishing practices

OCEAN ENVIRONMENTS

LOCATION Southern Indonesia, from Lombok in the west to Timor in the east

REEF FLAT OFF PANTAR ISLAND

This shallow reef area, featuring numerous species of stony coral and a starfish, is in east Nusa Tenggara.

Nusa Tenggara is a chain of around 500 coral-fringed islands in southern Indonesia. The northern islands are volcanic in origin, while the southern islands consist mainly of uplifted coral limestone. Many of the reefs have been only rarely explored. However, what surveys have been carried out

indicate an extremely high diversity of marine life in this region. For example, a single large reef can contain more than 1,200 species of fish (more than in all the seas in Europe combined), and 500 different species of reefbuilding coral. Common animals here include Eagle Rays, Manta Rays,

Humphead Parrotfish, and various species of octopuses and nudibranchs (sea slugs). Major threats to the reefs in Nusa Tenggara include pollution from land-based sources, removal of fish for the aquarium trade, and reef destruction by blast fishing. Coral bleaching affected some reefs in 2010.

161 PACIFIC OCEAN SOUTHWEST

Great Barrier Reef TYPE

Barrier reef

37,000 square km (14,300 square miles)

AREA

Damaged by tropical storms, pollution, and an unbalanced ecosystem

CONDITION

Parallel to Queensland coast, northeastern Australia

LOCATION

Australia’s Great Barrier Reef, which stretches 2,010km (1,250 miles), is the world’s largest coral reef system. Often described as the largest structure ever made by living organisms, it in fact consists of some 3,000 individual reefs and small coral islands. Its outer edge ranges from 30 to 250km (18 to 155 miles) from the mainland, and its biological diversity is high. The reef contains about 350 species of stony coral and many of soft coral. Its 1,500 species of fish range from 45 species of butterflyfish, to several shark species, including silvertip, hammerhead, and whale sharks. The reef is also home to 500 species of algae, 20 species of sea snake, and 4,000 species of mollusc.

PACIFIC OCEAN SOUTHWEST

Marshall Islands TYPE

Atolls

6,200 square km (2,400 square miles)

AREA

Generally good; some episodes of coral bleaching

CONDITION

Micronesia, southwest of Hawaii, western Pacific

LOCATION

REEF CHANNEL

In this view of a central area of the reef, a deep, meandering channel separates two reef platforms. The region’s high tidal range drives strong currents through such channels.

However, a study published in 2012 reported that the reef has lost more than half its coral cover since 1985. The factors causing this damage include pollution, tropical cyclones, raised water temperature causing mass coral bleaching, population outbreaks of the Crown-of-thorns Starfish, overfishing, and shipping accidents. The Marshall Islands consist of 29 coral atolls and five small islands in the western Pacific. The atolls lie on top of ancient volcanic peaks that are thought to have erupted from the ocean floor 50-60 million years ago. They include Kwajalein, the largest atoll in the Pacific at 2,500 square km (1,000 square miles), and Bikini and Enewetak atolls, which were used by the USA for testing nuclear weapons between 1946 and 1962. Human pressures on these two remote, evacuated atolls have been minimal during the past 50 years, and marine life around them now thrives; for example, 250 species of coral and up to 1,000 species of fish have been recorded at Bikini. MAJURO ATOLL

As with many Pacific atolls, the rim of Majuro Atoll consists partly of shallow submerged reef and partly of small, low-lying islands.

Hawaiian Archipelago Fringing reefs, atolls, submerged reefs

TYPE

1,180 square km (450 square miles)

AREA

Coral disease outbreaks reported

CONDITION

LOCATION

North-central Pacific

The Hawaiian Archipelago consists of the exposed peaks of a huge undersea mountain range. These mountains have formed over tens of millions of years as the Pacific Plate moves

northwest over a hotspot in the Earth’s mantle. Coral reefs fringe some coastal areas of the younger, substantial islands at the southeastern end of the chain, such as Oahu and Molokai. To the northwest, located on the submerged summits of older, sunken islands, are several near-atolls (such as the French Frigate Shoals) and atolls (such as Midway Atoll). These reefs are highly isolated from all other coral reefs in the world, and although their overall biological diversity is relatively low, many new species have evolved on them. The more remote reefs are healthy, but in 2013, a serious coral disease was reported affecting reefs on Oahu and Kauai.

One of the tiniest residents of the Great Barrier Reef, at just 7–8mm (less than 1⁄3in) long from snout to tail, is the Stout Infantfish. When discovered in 2004, the Infantfish was declared to be the world’s smallest vertebrate species. That title has since been claimed first by a slightly smaller species of Indonesian cyprinid fish, and more recently by a tiny species of frog, about 7mm (1⁄4in) long, found in Papua New Guinea.

PACIFIC OCEAN SOUTHWEST

Society Islands TYPE Fringing reefs, barrier reefs, atolls

recorded. The reefs’ health is generally good, but some reefs around the busy holiday destination islands of Tahiti, Moorea, and Bora-Bora have been severely affected by construction, sewage, and sediment run-off.

1,500 square km (600 square miles)

AREA

CONDITION Good, but significant local damage

French Polynesia, northeast of New Zealand, south-central Pacific

LOCATION

The Society Islands comprise a chain of volcanic and coral islands in the South Pacific, including islands with barrier reefs (such as Rai’atea), islands with both fringing and barrier reefs (such as Tahiti), and atolls or nearatolls (such as Maupihaa and Maupiti). The reefs’ biological diversity is moderate compared with the reefs of Southeast Asia, although more than 160 coral species, 800 species of reef fish, 1,000 species of mollusc, and 30 species of echinoderm have been

MOOREA

A wide fringing reef almost completely surrounds the shoreline of mountainous Moorea, part of which is visible in this view.

FRENCH FRIGATE SHOALS

Reef fish, including Longfin Bannerfish, Milletseed Butterflyfish, and Bluestripe Snappers, swim around a table coral.

OCEAN ENVIRONMENTS

PACIFIC OCEAN CENTRAL

THE WORLD’S SMALLEST VERTEBRATE?

THE GREAT BARRIER REEF

The warm, clear waters of the reef support an astonishing variety of life. Here, fairy basslets can be seen shoaling over vividly colored soft corals. Bright coloration can serve several purposes for reef fish, including helping members of a species to recognize each other and acting as a warning to predators.

164

SHALLOW SEAS

The Pelagic Zone THE PELAGIC ZONE IS THE WATER COLUMN ABOVE

LION’S-MANE JELLYFISH

This daunting giant of the plankton can grow up to 6 ft (2 m) across, with 200-ft (60-m) tentacles.

the continental shelf (although the term is also used to refer to the water column of the open ocean). It is a vast environment, and temperature and salinity variations within it result in distinct water masses. These are separated by “fronts” and characterized locally by different plankton. Coastal and shelf waters are more productive than the open ocean. When calm, the water stratifies, cutting off the surface plankton from essential nutrients in the layers below. Storms cause the layers to mix, stimulating phytoplankton blooms. High latitudes have seasonal plankton cycles; in warmer waters, seasonal upwelling of nutrient-rich deeper water triggers phytoplankton growth.

Microscopic Productivity Much of the primary productivity in the world’s oceans and seas occurs over the continental shelves. Tiny phytoplankton floating in the surface waters harness the Sun’s energy through photosynthesis to produce living cells. Some of the tiniest algae (picoplankton) are thought to supply a considerable amount of primary production. As well as sunlight, nutrients and trace metals are needed for phytoplankton growth. These are PRIMARY PRODUCTION often in short supply in the open This satellite map shows variations in ocean, but shelf waters benefit from a primary production, indicated by the continual input from rivers, mixing by concentration of the pigment waves and, on some coasts, the chlorophyll a in the oceans and the amount of vegetation on land. upswelling of nutrient-rich water.

DRIFTING ZOOPLANKTON

OCEAN ENVIRONMENTS

Continental shelf zooplankton contains many larvae of sea bed animals that then drift away to new areas.

CHLOROPHYLL A CONCENTRATION LOW

HIGH

VEGETATION INDEX MIN

MAX

The Plankton Cycle

Riding the Currents

In temperate and polar seas, optimal phytoplankton growth occurs in both spring and summer. There are long daylight hours and maximum nutrient levels after winter storms have mixed the water column and resuspended dissolved nutrients from the seabed. The well-known spring blooms can rapidly turn clear seawater into pea soup, or a variety of other colors, depending on the organism. Typically, there is a succession of phytoplankton species with short blooms. Responding to abundant food and increasing temperatures, tiny zooplankton begin grazing the phytoplankton and reproducing. Bottom-living coastal animals release clouds of larvae to feed in the nutritious broth, before taking up life on the sea bed. Spawning fish also contribute a mass of eggs and larvae. Eventually, the phytoplankton is grazed down, nutrients are exhausted, and productivity drops off, in an annual cycle that will be renewed again next spring.

From tiny algae to giant jellyfish, the animals and plants of the plankton either float passively or swim weakly. This is mainly to keep them up in the sunlit surface waters, where most production occurs; these drifters must go wherever the currents take them. On most continental shelves, there is a residual drift in a particular direction, although wind-driven surface currents, where most of the plankton live, can move in any direction for short periods. Some animals go on long migrations to spawn, relying on residual currents to bring their larvae back to areas suitable for their growth into adults; for example, conger eel larvae take around two years to drift back from their spawning grounds far off the continental shelf. The larvae of the majority of coastal animals, including those of barnacles, mussels, hydroids, and echinoderms, spend much shorter periods in the plankton—just long enough to disperse to new areas of coast. However, the plankton is a dangerous place, full of hungry mouths and tentacles, and though millions of eggs and larvae are released, the vast majority of planktonic feeders will die; only a lucky few find a suitable place to settle and grow.

HUMAN IMPACT

RED TIDE A rapid increase in a population of marine algae is called a bloom. This bloom on the Scottish coast, known as a red tide, was caused by the dinoflagellate Noctiluca scintillans. Sometimes blooms poison marine life. Often, the sheer numbers of organisms clog fish gills, suffocating them. Dense blooms occur naturally, but man-made pollution from nutrient runoff into the sea may also feed these blooms, making them more frequent and extensive.

COLONIZED ROPE

This rope was colonized over the course of a year by sea squirts, feather stars, fan worms, and anemones, their planktonic larvae having been transported by ocean currents.

165

MIGRATORY SHOALS

Pelagic fish such as these mackerel move around the ocean in response to temperature changes. They are among the pelagic zone’s larger predators.

Pelagic Fisheries

The animals of the plankton, especially small crustaceans such as copepods and krill, are eaten by fish, mainly small, shoaling species such as herring, sand eels, sardines, and anchovies. Most of these fish live permanently in midwater, using the seabed only to spawn or to avoid predators. They are strong swimmers (nekton), using speed to catch prey and evade predators. They can travel long distances against residual currents to feed and also to reach their spawning grounds. Small, shoaling fish are, in turn, food for larger predators, such as squid, tuna, cetaceans, NEKTONIC INVERTEBRATE and sharks. Whale sharks, basking Squid are the only invertebrates sharks, and baleen whales are among that swim strongly enough to be the largest of the marine animals, yet classed as nekton. They catch a variety of prey including fish and they feed directly on plankton, planktonic crustaceans. consuming vast quantities.

Continental shelf waters support massive quantities of pelagic fish, ultimately sustained by abundant plankton. The most important fisheries are for herring, sardines, anchovies, pilchards, mackerel, capelin and jackfish. Squid are also fished commercially. Many fish stocks are under severe pressure as boats and nets get bigger and the technology to pinpoint shoals becomes ever more sophisticated. Pelagic fish and squid are caught in drift nets that hang about 30 ft (10 m) down from the surface. In the north Pacific, some 105,000 miles (170,000 km) of drift net is available to major fisheries; unfortunately, these nets also trap cetaceans, turtles, and diving birds. Drifting longlines are used for tuna and swordfish; these also catch juvenile fish, sharks, turtles, and seabirds. Midwater trawls capture vast quantities of shoaling fish such as herring, mackerel, and sardines. Small-scale fisheries for a wide variety of other pelagic species are important in sustaining local coastal communities worldwide.

FOOD CHAIN THREAT

Sand eels are food for sea-birds (such as this Arctic tern), seals, cetaceans, and larger fish. Despite their importance at the base of many food chains, vast quantities are taken by fisheries for feeding to livestock and farmed fish, and are burned as fuel oil.

OCEAN ENVIRONMENTS

Active Swimmers

THE STEEL-BLUE WAVES of the open ocean

conceal an extraordinary landscape, where the continents plunge down to a vast, undulating, muddy plain. Here, the ocean water column supports layer upon layer of life, from the surface zone, powered by sunlight, to the crushing pressure of the darkest depths. In places, the abyssal plain is broken by underwater volcanoes or by mountain ranges high enough to rival the Himalayas. Springs of super-hot water emerge from these mountainsides, supporting living communities unlike any others on the planet. Elsewhere, Earth’s vast tectonic plates collide, ripping trenches in the ocean floor and stimulating powerful earthquakes. Yet fewer people have explored these mysterious depths than have flown in space.

TH E OP E N O C E A N A N D OC E A N F L O O R BENEATH THE WAVES

In the deepest ocean, an underwater Mount Everest could be hidden beneath these waves—and still leave plenty of space to put the Burj Khalifa (the world’s tallest building) on top. As a result, we have better maps of the Moon than of the deep seabed.

168

THE OPEN OCEAN AND OCEAN FLOOR

OCEAN ZONES

SUNLIT ZONE 0–660 ft

Zones of the Open Ocean CONDITIONS IN THE OCEAN

vary greatly with depth. Light and temperature changes occur quickly, while pressure increases incrementally. Although many of these changes are continuous, the ocean can be divided into a series of distinct depth zones, each of which produces very different conditions for living things.

The Surface Layer The top three feet of the ocean is the richest in nutrients. This upper layer is sometimes called the neuston, although this term is also used for the animals that live there, such as jellyfish. Amino acids, fatty acids, and proteins excreted by plants and animals float up into this surface layer, as do oils from the decomposing bodies of dead animals. These produce a rich supply of nutrients for phytoplankton. The top three feet of seawater is also the interface where gas exchange takes place between the ocean and the atmosphere. This is vitally important to all life on Earth, as half of the oxygen animals need for survival comes from the ocean. Not surprisingly, phytoplankton gathers in this surface zone in daylight, as do the animals that feed on them. This zone is also highly susceptible to chemical pollution and floating litter, which can be deadly for marine life. NOCTURNAL AND DIURNAL DISTRIBUTION

Only a small proportion of marine life inhabits the deep zone; the majority live above 3,300 ft (1,000 m). The sunlit zone is dangerous for animals—many stay in the twilight zone by day and only go upward at night. The sunlit zone is much emptier by day. NIGHT

OCEAN ENVIRONMENTS

DAY 10% sunlit zone

40% sunlit zone

75% twilight zone

50% twilight zone

15% deep zone

10% deep zone

HUMAN IMPACT

FREE DIVING When divers breathe compressed air underwater, excess nitrogen dissolves in their blood, and they risk the bends if they surface too fast. Free divers avoid this by holding their breath underwater. Pressure squeezes their lungs, but the surrounding blood vessels swell to protect them, and blood nitrogen levels stay safe. Trained free divers can hold their breath long enough to reach 660 ft (200 m), using aids to help them descend and ascend.

Seawater rapidly absorbs sunlight, so only one percent of light reaches 660 ft (200 m) below the surface. Phytoplankton use the light to photosynthesize, forming the base of food chains. This zone drives all ocean life.

TWILIGHT ZONE 660–3,300 ft Too dark for photosynthesis, but with just enough light to hunt by, many animals move from this zone into the sunlit zone at night.

DARK ZONE 3,300 ft–13,100 ft Almost no light penetrates below 3,300 ft (1,000 m). From here to the greatest depths, it is dark, so no plants can grow, and virtually the only source of food is the “snow” of waste from above. Temperatures down here are a universally chilly 35–39oF (2–4oC), and the pressures so extreme that only highly adapted animals can survive. The dark zone is defined as continuing down to the abyssal plain, below 13,100 ft (4,000 m). Technically, all the water below 3,300 ft (1,000 m) is a dark zone, where the only light comes from bioluminescent animals (see p.224). However, for convenience, the waters below the dark zone can be further subdivided.

ABYSSAL ZONE 13,100–19,700 ft Beyond the continental slope, the sea bed flattens out. In many areas, it forms vast plains at depths below 13,100 ft (4,000 m). Some areas drop deeper to a sea floor that undulates down to depths of 19,700 ft (6,000 m). Around 30 percent of the total seabed area lies between these depths. Animals living here move up and down through a narrow column above the sea bed, called the abyssal zone.

HADAL ZONE 19,700–36,100 ft The sea floor plunges below 19,700 ft (6,000 m) in only a few deep ocean trenches. This hadal zone makes up less than 2 percent of the total seafloor area. Fewer than 10 human beings have ever visited this zone (see p.183), and the pressures are so high that only a few submersibles are able to operate here. As yet, little is known about life at these depths, although anemones and jellyfish have been observed at a depth of 27,000 ft (8,221 m) and a fish has been dredged from a depth of 27,500 ft (8,370 m). Amphipods, as well as amoebae and various other microbes, have been found living at the bottom of the Mariana Trench, the deepest point in the oceans.

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ZONES OF THE OPEN OCEAN

DEEPEST OCEAN POINTS

ne Mari

The column below shows the average depth (yellow band) and greatest depth (red band) of the oceans and some of the world’s seas.

Life lphin

o m) d (201 9 ft ) 5 6 m • (300 48 ft • 1,1g penguin in k m) (680 hark s 30 ft • 2,2 at white ) m 0 gre 0 ,0 t (1 e l 00 f • 3,3 rm wha m) 00 spe t (1,2 turtle 37 f • 3,9therback ) 0m lea (1,58 3 ft seal 8 1 , t • 5 phan ele

The Sunlit Zone

North Sea average depth 308 ft (94 m) Baltic Sea greatest depth 1,473 ft (449 m) North Sea greatest depth 2,296 ft (700 m) Arctic Ocean average depth 3,248 ft (990 m) Mediterranean Sea average depth 4,921 ft (1,500 m) Caribbean Sea average depth 4,960 ft (1,512 m)

almost one-third of the total sea-bed area is made up of abyssal plains at around 14,800 ft (4,500 m).

Atlantic Ocean average depth 10,925 ft (3,330 m)

169

CRYSTAL WATERS

Crystal-clear tropical waters look idyllic, but the clarity indicates that there are few nutrients and therefore few phytoplankton in the water. As a result, feeding for animals is quite poor.

The sunlit zone is the range in which there is enough sunlight for photosynthesis. The ocean absorbs different wavelengths of sunlight to differing extents (see p.36). Nearly all red light is absorbed within 30 ft (10 m), so red animals look black below this depth. Green light penetrates much deeper in clear water, down to around 330 ft (100 m), and blue light to twice that. Due to the presence of chlorophyll, phytoplankton preferentially absorb the red and blue portions of the light spectrum (for photosynthesis) and reflect green light. They can photosynthesize down to about 660 ft (200 m) in clear water. In cloudy water, the sunlit zone is shallower, because light is absorbed more quickly. The accumulations of phyto- and zooplankton in fertile waters absorb sunlight, reducing the depth of the sunlight zone. Phytoplankton must stay in the sunlit layer during daylight to photosynthesize. Zooplankton follows them there to feed, along with animals that feed on zooplankton. This zone is dangerous because light makes animals conspicuous to their hunters.

Indian Ocean average depth 12,762 ft (3,890 m) Pacific Ocean average depth 14,041 ft (4,280 m) Southern Ocean average depth 14,763 ft (4,500 m)

Mediterranean Sea greatest depth 16,715 ft (5,095 m) (Hellenic Trough) Arctic Ocean greatest depth 18,377 ft (5,601 m) (Molloy Deep)

Southern Ocean greatest depth 23,466 ft (7,152 m)

FEEDING IN THE SUNLIT ZONE

The phytoplankton of the sunlit zone is the food of zooplankton. Larger animals, such as these shrimp, in turn feed on zooplankton. Phytoplankton is at the bottom of most ocean food chains.

Caribbean Sea greatest depth 25,213 ft (7,685 m) (Caymen Trench) Indian Ocean greatest depth 25,344 ft (7,725 m) (Java Trench)

Atlantic Ocean greatest depth 29,404 ft (8,962 m) (Puerto Rico Trench)

Pacific Ocean greatest depth 35,829 ft (10,920 m) (Mariana Trench)

ZONES OF LIFE

The different zones of life in the deep ocean are shown here, together with the depths reached by humans and a selection of marine animals. Most life is concentrated above 3,300 ft (1,000 m), where there is some light.

Phytoplankton must remain in the sunlit zone if it is to catch enough sunlight for photosynthesis. This zone is the warmest and richest in the nutrients needed for growth. It would be counterproductive to expend huge amounts of energy to stay in this zone, so phytoplankton has developed a wide range of mechanisms to help it hang there effortlessly. Buoyancy bubbles, droplets of oil, or stores of light fats keep some species afloat. Others are covered in spines, which increase their surface area and help buoy them up. Some phytoplankton forms colonial chains, which produce more drag in water and slow the rate at which the phytoplankton sink. One group, called dinoflagellates, have threadlike flagellae that let them swim weakly. In this highly productive zone, phytoplankton produces half of the oxygen in the atmosphere. In temperate regions, phytoplankton proliferates in summer, sometimes forming dense blooms.

DIATOM

Diatoms are a very prolific type of phytoplankton. Some grow colonially, attached to rocks in chains or mats. Each year, six billion tons of phytoplankton grow in the oceans worldwide.

ZOOPLANKTON

This sample of zooplankton, collected in a net, includes an echinoderm (bottom left), a radiolarian, and a crab larva (center), with a fish egg (bottom right).

OCEAN ENVIRONMENTS

Beyond the abyssal plains, undulating, rocky seabed stretches down to around 19,700 ft (6,000 m). Only the ocean trenches reach deeper.

Living in the Sunlit Zone

170

THE OPEN OCEAN AND OCEAN FLOOR

Plankton and Nekton

The Twilight Zone

In spring, as phytoplankton blooms begin to develop, zooplankton start multiplying. They follow the phytoplankton into the sunlit zone to feed. Most are herbivores that feed on phytoplankton; some are carnivores that hunt other zooplankton. Many are classed as meroplankton—the young of animals like crabs, lobsters, barnacles, and some fish—which have a planktonic larval stage and use the currents to spread. By taking advantage of the summer phytoplankton feast, they avoid competing for food with adults of their own kind. While plankton drift with the currents, many free-swimming animals (collectively called nekton) gather to feed on them: fish, squid, marine mammals, and turtles. These, in turn, are food for predatory fish and seabirds. Some larger animals, such as basking sharks, also feed on zooplankton and nekton. SARGASSUMFISH

Here, two Sargassumfish are hiding in Sargussum seaweed, floating on the surface of the Sargasso Sea.

GIANT FILTER-FEEDER

OCEAN ENVIRONMENTS

More than 36 ft (11 m) long, basking sharks like this one scoop up shoals of plankton, then filter them from the water with the white gill rakers inside their jaws.

In the twilight zone, there is just enough light for animals to see—and be seen. As a result, predators and prey are in constant battle. Many species are almost totally translucent, to avoid casting even a faint shadow. Others are reflective, to disguise themselves against the light from above, or have wafer-thin bodies that reduce their silhouette. To cope with dim light, many animals in this zone have large eyes. COPEPOD The main source of food here is detritus. Copepods are herbivores. They Many animals therefore migrate upward into make up 70 percent of the total the sunlit zone, where food is plentiful, at zooplankton population, with thousands in a cubic yard. night, returning to the twilight zone as the Sun rises. Millions of tonnes of animals, equivalent to around 30 percent of the total marine biomass, make this daily trek—by far the largest migration of life on Earth. The length of the journey is a matter of scale. Small planktonic animals measuring less than 1mm (1/25 in) in length may only migrate through 20 m (70 ft), but some larger shrimp travel 600 m (2,000 ft) each way, every day.

ZONES OF THE OPEN OCEAN

The Dark and Abyssal zones

SQUID OF THE OPEN OCEAN

Squid live in several zones of the ocean, from the sunlit zone, where this big-fin reef squid is found, to the deep zone. Deep-sea squid are difficult to photograph and are often photographed only as dead specimens.

The waters below the twilight zone are all dark, cold, subject to high pressure, and impoverished in food. For animals adapted to these deep zones, pressure is not a problem: their liquid-filled bodies are almost incompressible, compared to the gasfilled bodies of surface-living birds and mammals, which are much more easily compressible and subject to the effects of pressure. Most fish use gases in their swim bladders to maintain buoyancy, and these are susceptible to pressure change. Many deep-water fish therefore have no functional swim bladders. For most deep-water species, lack of food is the biggest problem: only about five percent of the energy that plants produce at the surface filters down to these depths. Animals of the deep are typically slow-moving, slow-growing, and long-lived. They conserve energy by waiting for food to come to them. Many therefore have massive mouths and powerful teeth. Others use tricks to catch prey: anglerfish dangle lures, and some species even harbor luminescent bacteria or use chemical processes to make these lures and other structures glow.

SPOOKFISH

mucus on body attract bacteria, which protect it from heat

DISCOVERY

THE CHALLENGER Many oceanographic discoveries were made by HMS Challenger, a converted British warship that made a 68,900mile (110,900 km-) voyage around the oceans from 1872 to 1876, collecting depth soundings as it went. In March 1875, near Guam, it dropped a sounding line to a depth of 26,850 ft (8,184 m) and collected clay to prove this was the seabed. By good luck, the ship was over the Mariana Trench, close to the deepest spot in the ocean, now appropriately called the Challenger Deep.

171

The brownsnout spookfish is found at depths of up to 3,300 ft (1,000 m), on the boundary of the dark zone. Its bones are so thin that it is almost transparent, and its large eyes look upward to spot predators attacking from above. It feeds mainly on copepods, and gives birth to live young that float in the plankton.

red tentacles around head gather food and provide sensory information

HEAT-TOLERANT WORM

This polychaete worm (a type of segmented worm) was discovered by the Alvin submersible in 1979— and named Alvinella pompejana in its honor. It is the most heat-tolerant animal on Earth, living near water emerging from hydrothermal vents at 570˚F (300˚C).

The Hadal Zone

DEEP SQUEEZE

ALVIN SUBMERSIBLE

Alvin is designed to withstand the extreme pressure of the deep zone and has enabled scientists to make many important discoveries during over 4,000 dives.

FANGTOOTH FISH

The fangtooth has been recorded at depths of 16,380 ft (4,992 m). Like many deep-water fish, it has a large head and massive teeth. Sensory organs along its body detect prey movement in the dark.

OCEAN ENVIRONMENTS

A polystyrene cup attached to the outside of a submersible resurfaces at a fraction of its original size, illustrating the effects of pressure in the deep ocean.

Few deep-water species have been observed in their natural environment of the hadal zone and even fewer photographed. Many species are known only from samples dredged up in nets, and most photographs are of dead specimens (including the fangtooth on the right). Sometimes deep-sea animals can be studied in aquariums, but many species cannot survive temperature and pressure changes when brought to the surface. Although many of the animals here hunt each other, the food chain must begin with a supply of food from above. Whereas animals on the seabed can patrol large areas to find food particles accumulated there over weeks and months, animals in midwater must grab food particles in the short time when they float downward past them, which is much trickier. Only a small proportion of the detritus from above is harvested in midwater, so food is always scarce. Scientists observing this zone often see the same species repeatedly. The environment of this zone is remarkably uniform worldwide and there are few physical or ecological barriers to block the movement of species. Many deep-water species therefore are widely distributed, and several are found in every ocean. As a result, species diversity is low: only around 1,000 of the known 29,000 fish species live at this depth.

GLOBAL EXPLORER

The Global Explorer is an ROV that can dive to 10,000 ft (3,045 m). Controlled by the mother ship through a cable, it can take photographs of the sea floor.

173

Exploration with Submersibles Submersibles are underwater vehicles, smaller than

scuba diver C-Quester Deepflight Super Falcon nuclear submarine White shark Pisces class DSV gulper eel Hercules ROV

3,300 ft (1,000 m)

6,500 ft (2,000 m) 9,800 ft (3,000 m) 13,100 ft (4,000 m)

16,400 ft (5,000 m) shinkai

19,700 ft (6,000 m)

jiaolong

23,000 ft (7,000 m) 26,300 ft (8,000 m) 29,500 ft (9,000 m)

Deepsea Challenger Nereus ROV

32,800 ft (10,000 m) 36,100 ft (11,000 m)

SHALLOW EXPLORATION

C-QUESTER Developed by Netherlandsbased company U-boat Worx, C-Quester submersibles allow one or two people to explore down to 330 ft (100 m).

PISCES IV An example of a Deep Submergence Vehicle (DSV) used in scientific research, Pisces IV is owned and operated by the Hawaii Undersea Research Laboratory. It carries three people and can operate down to 6,600 ft (2,000 m).

SHINKAI 6500 Launched in 1989 by the Japan Marine Science and Technology Center, Shinkai 6500 is one of the deeper-diving DSVs. In June 2013, it transmitted the world’s first live broadcast from 16,500 ft (5,000 m).

HERCULES ROV A fairly typical ROV, Hercules can descend to a depth of 13,500 ft (4,000 m) and take high-definition images. It is equipped with six thrusters that allow it to “fly” in any direction, like a helicopter. Slightly positively buoyant, it will gently float up to the surface if its thrusters stop turning.

DEEPSEA CHALLENGER This 24-ft- (7.3-m)- long submersible reached the Challenger Deep in March 2012, carrying the film director James Cameron. In doing so, it won what had been called the “race to inner space”—the first solo manned mission to reach the deepest spot in the oceans.

OCEAN ENVIRONMENTS

Alvin

Sea Level

MULTI-PERSON DEEPWATER RESEARCH

Recreational vehicles, such as the Super Falcon, generally descend to depths of no more than 660 ft (200 m). Most DSVs and ROVs have maximum depths varying from 3,300 ft (1,000 m) to 23,000 ft (7,000 m), but a few can go to the deepest spot in the oceans, the Challenger Deep of the Mariana Trench at 36,100 ft (11,000 m). As of early 2014, only two DSVs (including Deepsea Challenger) and two ROVs —Kaiko (Japan) and Nereus (US) have ever achieved this feat.

DEEPFLIGHT SUPER FALCON The latest of several submersibles designed by American engineer Graham Hawkes, the Super Falcon is an underwater vehicle intended mainly for private recreational exploration. It “flies” through the water, carrying two people down to 400 ft (120 m).

REMOTELY OPERATED VEHICLES (ROVS)

Into the Deep

TYPES OF SUBMERSIBLES

RACE TO INNER SPACE

submarines, used mainly for exploration, scientific study of the oceans, and recreation. First developed in the 1960s, they have helped open up the deep ocean to exploration. Modern submersibles include manned vehicles of various types and Remotely Operated Vehicles (ROVs), which are unmanned Remotely Operated Vehicles. Some recent designs no longer depend on ballast and buoyancy tanks to control descent and ascent, instead using technologies originally developed for flight. A famous manned submersible is Alvin, operated by the Woods Hole Oceanographic Institute (US). In 1977, Alvin’s crew discovered the first hydrothermal vents (see pp. 188-89) and, in 1986, it was involved in exploring the wreckage of the Titanic. During 20112013, Alvin underwent a complete rebuild. Along with Shinkai 6500 (Japan), Jiaolong (China), and others, it belongs to a class known as Deep Submergence Vehicles or DSVs. These are mostly used for scientific research. Other submersibles include ROVs, which are usually connected to a surface vessel by a tether, and those used mainly for shallow water recreation. The more sophisticated ROVs can drill cores in the sea floor and take sonar surveys, as well as record images.

174

THE OPEN OCEAN AND OCEAN FLOOR

Seamounts and Guyots SEAMOUNTS ARE TOTALLY

submerged, undersea mountains that rise at least 3,300 ft (1,000 m) from the sea floor; smaller ones are called sea knolls. Guyots are seamounts that once rose above sea level—as a result, they have a flat top caused by erosion. Often isolated in deep ocean, seamounts and guyots provide a habitat for marine life adapted to shallower water. The obstruction of a seamount forces nutrient-rich, deep-sea currents to rise closer to the surface, forming eddies above the seamount. These trap nutrients and support plankton, which in turn attract shoals of fish.

Geological Origins

HENRY GUYOT Arnold Henry Guyot (1807–1884) was the first professor of geology at Princeton University. He set up a system of weather observatories that led to the formation of the US Weather Bureau. Guyots were named in his honor by a later Princeton geology professor, Harry Hass. Hass discovered guyots using echo-sounding equipment during World War II.

EVOLUTION OF A GUYOT

Seamounts start as undersea volcanoes, where a rift in the sea bed allows volcanic eruptions. Many arise at rifts on the crest of mid-ocean ridges, formed by the movement of tectonic plates (see p. 185). Because these rifts are generally linear, seamounts tend to be elliptical or elongated in shape. They are made of volcanic basalt rock, but a thin layer of marine sediment accumulates over time. Seamounts often occur in chains or elongated groups, either because there are several weak spots along a rift, or because a series of seamounts originated sequentially at a single, stationary volcanic hotspot. Sometimes volcanic eruptions break above the ocean surface to form island chains, and these may continue out to sea as a line of guyots, or tablemounts. Newly formed volcanic rock is easily eroded, so over time, the above-water peak of the volcanic island is eroded down to a flat top. Then, as the ocean plates carry it away from the zone of SEAMOUNT FORMATION volcanic activity, the A seamount forms from an flat-topped guyot sinks underwater volcanic eruption. beneath the surface. Erosion here is slower than on

direction of plate movement

A

B

A guyot (A) begins life when a volcano erupts above a “hotspot,” creating a small volcanic island.

1

C

A

Over millennia, erosion reduces the island to a flat top at sea level, while it (A) moves away from the hotspot. A new island (B) forms.

2

B

As the island moves farther, it sinks and forms a guyot. New islands (B and C) erupt from the hotspot.

3

Upwellings

land, so it remains conical.

World Distribution

OCEAN ENVIRONMENTS

PEOPLE

There may be 100,000 seamounts and guyots in the oceans, but few have been mapped or explored and the total number is unknown. Seamounts may occur either singly or in clusters or chains, reflecting zones of past volcanic activity. The Pacific, with its Ring of Fire, is the most volcanically active ocean, containing over 30,000 seamounts and guyots. Pacific chains typically form in a northwesterly direction, matching the direction of plate movement, with 10 to 100 seamounts in each chain, sometimes connected by an undersea ridge. In the Atlantic and Indian oceans, by contrast, seamounts mostly occur singly. DISTRIBUTION MAP OF SEAMOUNTS

Some seamounts and guyots arise over volcanic hotspots, often in chains. Others form singly along mid-ocean ridges. Total numbers are unknown.

The open ocean is mainly barren, because cold, nutrient-rich currents are confined to deep water, far beneath the reach of plankton. Seamounts—which stand up to 13,000 ft (4,000 m) above the sea bed— form a major obstruction to these currents, diverting them and pushing them upward. This brings an upwelling of nutrients into the sunlit zone, and allows phytoplankton to flourish. As these nutrient-rich currents rush over the top of the seamount, they split in two and sweep around it. This makes the water above the seamount rotate, encircling a cylindrical column of still water that trapped nutrients spiral and plankton extends high above the height flow still of the seamount. This “virtual” water cylinder is called a Taylor Column. Above a seamount, it forms an area of backeddies and still water in which nutrients accumulate and plankton get trapped. upwelling This creates a zone of incredible richness and seamount productivity above the seamount—an “oasis” flow splits in the nutrient desert of the open ocean. deep-water current

WATER COLUMNS

The currents spiraling around and over a seamount create a column of still water above it. Plankton thrive on the nutrients trapped there.

A

SEAMOUNTS AND GUYOTS MOUNTAINS IN THE SEA 8,850 ft (2,700 m) 9,000 ft (2,750 m) 9,200 ft (2,800 m) 9,350 ft (2,850 m)

chain of large seamounts

This false-color map shows how a chain of seamounts has arisen, close to where two spreading tectonic plates have been displaced sideways by a transform fault. Other seamounts occur singly away from the ridge.

175

N

isolated seamount

transform fault isolated guyot

crest of East Pacific Rise

9,500 ft (2,900 m) 9,700 ft (2,950 m) 9,850 ft (3,000 m) 10,000 ft (3,050 m) 10,200 ft (3,100 m) 10,300 ft (3,150 m) 10,500 ft (3,200 m) 10,700 ft (3,250 m) 10,800 ft (3,300 m) 11,000 ft (3,350 m) 11,150 ft (3,400 m) 11,300 ft (3,450 m) 11,500 ft (3,500 m) 11,650 ft (3,550 m) 11,800 ft (3,600 m) 12,000 ft (3,650 m) 12,150 ft (3,700 m)

East Pacific Rise

12,300 ft (3,750 m)

fracture zone

12,500 ft (3,800 m) HUMAN IMPACT

ROUGHY TROUBLE

DEPTH

Life on a Seamount

PRIMNOID CORAL THREAT

Scientists fear some primnoid coral species may be wiped out by bottom-trawl fishing before they have even been named.

FEEDING FROM THE CURRENTS

This squat lobster, or pinch bug, is a scavenger living on rock faces. Currents welling over the Bowie Seamount in the northeast Pacific supply rich pickings.

SEAMOUNT FEEDER

Found in the tropics, this octocoral is a colony of soft corals. The feeding polyps, lined up along the branches, catch food from currents sweeping over the seamount.

OCEAN ENVIRONMENTS

Some seamounts were first detected when fishermen discovered large shoals of fish in the area. The nutrient-rich waters trapped above seamounts support dense concentrations of phytoplankton as well as the zooplankton that feed on them. Free-swimming animals are attracted by this feast, including fish at densities found nowhere else in the open ocean. Predators such as sharks and seals also gather to feed. Seamount rock is colonized by suspension feeders—animals that catch plankton and detritus as it floats past. Only about one in a thousand seamounts has been explored underwater. However, in studies of 25 seamounts in the Tasman and Coral seas, 850 species (some previously thought extinct) were recorded. Seamounts are important biodiversity hotspots, with up to one-third of species found there restricted to a single seamount or group of seamounts.

Fishermen thought they had found a bonanza in the 1980s when they discovered the huge shoals of fish that live over seamounts. For example, they could catch 100 tons of orange roughy (see below and p.352) in a single day. However, roughy, which can live for almost 150 years, is slow-growing, and does not produce eggs until it is 20–30 years old. Such heavy fishing cannot be sustained. World catches have declined hugely, and the roughy is now in danger.

176

THE OPEN OCEAN AND OCEAN FLOOR

The Continental Slope and Rise THE CONTINENTAL SLOPE AND RISE

CONTINENTAL MARGIN

are areas of sloping sea floor that lead from the continental shelf to the abyssal plain. Beyond a point on the shelf called the shelf break, the sea bed begins to drop more steeply. This is the continental slope, which leads into the open ocean. It sweeps down to 9,800–14,800 ft (3,000–4,500 m), where the seabed flattens out. In places, the slope is broken by submarine canyons. Sediments wash down these canyons, and accumulate at the base of the slope in a gentler gradient, forming the continental rise.

A typical continental margin is shown here, including the transition from a shoreline to the abyssal plain via the continental shelf, slope, and rise. The continental slope is about 87 miles (140 km) wide, and the continental rise is about 60 miles (100 km) wide. The vertical scale has been exaggerated: the continental slope actually has a gentle gradient, of about 1 in 50 (2 percent); and the rise is even gentler, at about 1 in 100 (1 percent).

submarine canyon shelf break— around 660 ft (200 m) below surface

slumped sediments form continental rise

Continental Slope The rock of the continental slope is blanketed by sediments washed from the land that have accumulated over millions of years. Crustaceans, echinoderms, and many other animals live in, or on, these sediments. The slope is dissected by deep canyons. These have been cut by an abrasive mix of sediment and water, called turbidity currents, which flow down the gorges at 50–60 mph (80–100 km/h). Some submarine canyons are massive: the Grand Bahama Canyon in the Caribbean has cliffs rising 14,060 ft (4,285 m) from the canyon floor. Many canyons are seaward extensions of great rivers. At the canyon end, the sediment is deposited as a spreading outwash fan, extending far out onto the abyssal plain.

outwash fan at foot of canyon

large outwash fan extending onto abyssal plain

erosion gullies

CANYON AND GULLIES

This sonar image shows a deep submarine canyon in the continental slope off Sodwana Bay, in KwaZulu Natal, South Africa.

submarine canyon

OCEAN ENVIRONMENTS

Life on the Continental Slope

CATCHING SABLEFISH

Sablefish are caught with longlines, 2/ 3 mile (1.2 km) long, that reach down toward the continental slope.

Like the shelf, the continental slope is enriched by nutrients washed off the land. This helps support both midwater (pelagic) and bottom-dwelling (demersal) fish. Fish stocks over most continental-shelf regions have declined dramatically in recent decades, as a result of overexploitation and poor management, driving more fishermen to seek deeper-water species over the continental slope. Unfortunately for fisheries, although deep-water species are SABLEFISH long-lived, they breed slowly, and stocks take a Sablefish breed slowly, it takes 14 years long time to recover. So and to replace each fish many fisheries are now caught. Fish farms (right) in serious decline. may be a better option.

ABYSSAL PLAIN This flat plain is formed by a deep accumulation of sediments. It typically lies at a depth of 15,000 ft (4,500 m).

THE CONTINENTAL SLOPE AND RISE

past shoreline formed by higher sea level in past

submarine canyon extends from shelf to abyssal plain

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some sediments deposited as delta at river mouth

sediments carried down river to sea

present shoreline

material from uplands is gradually eroded and washed into rivers

GANGES DELTA

The Ganges River carries 2 billion tons of sediment a year. Some is deposited in this massive delta. More is carried out to sea where it forms a deep-sea fan over the Bay of Bengal. TUBE ANEMONES

These sea anemones bury their bodies in sediment, at depths of 13,100 ft (4,000 m), feeding with their tentacles.

DISCOVERY SHORELINE Shorelines are shaped by erosion and deposition and move with changing sea levels.

CONTINENTAL RISE Deeper sediments build up, creating a gentle gradient of less than 1 in 100.

CONTINENTAL SLOPE The slope drops to 9,800 ft (3,000 m) at a gradient of 1 in 50.

COASTAL PLAIN An area of low-lying, flat land between the uplands and the sea.

CONTINENTAL SHELF The continental shelf is typically 460–660 ft (140–200 m) below the surface. Its width varies greatly.

Continental Rise

SEDIMENT FEEDER

Brittlestars are among the most common animals found feeding on the sediment of the continental rise. central disk

mouth (on underside of disk) five arms, arranged radially

LIZARDFISH HABITAT

The highfin lizardfish is found on the abyssal plain and continental rise, typically below about 6,600 ft (2,000 m), in water colder than 39ºF (4ºC).

STAKING A CLAIM Lured by vast oil reserves, oil companies have begun drilling in waters as deep as 7,550 ft (2,300 m) on the continental slope. These waters are also increasingly important for fisheries, so coastal countries want to establish national waters where they have sole rights to these resources. Under current maritime law, the rights of a coastal state over certain resources, such as oil, extend out to the continental margin—essentially to the boundary between continental rise and abyssal plain—or to 200 nautical miles from the coast, whichever is the greater (but never exceeding 350 nautical miles).

OCEAN ENVIRONMENTS

The continental rise is a thick wedge of sediment, up to 9 miles (15 km) deep, formed from material that has slumped downward to the base of the continental slope. This wedge drops gently away toward the abyssal plain. These sediment mounds are particularly extensive where several deep-sea fans meet and coalesce at the foot of submarine canyons. The geological boundary between the continental and oceanic crusts is completely obscured beneath these sediments. The sediments of the continental rise merge into the abyssal plains beyond. Brittlestars and polychaete worms, a type of segmented worm, live on the sediments, surviving on detritus falling from above. Atlantic red crabs scavenge on the seabed, migrating up the continental slope to breed. Deep-sea cod, Dover sole, rockfish, goosefish, and thornyheads are among the demersal species living on the slope and rise.Trawling has damaged many of these habitats, but the deeper canyons remain havens of biodiversity.

MOUNTAINS These rocks formed on an ancient sea bed and were later uplifted. Erosion will eventually return them to the sea.

COLD-WATER COMMUNITY

A squat lobster shelters among the polyps of the cold-water stony coral Lophelia pertusa, or tuft coral, in a Norwegian fjord.

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Cold-water Reefs

The map below shows the global distribution of cold-water reefs. Some of these reefs are small, while others cover up to 770 square miles (2,000 square km), although the map dots exaggerate their extent. The many reefs detected in the north Atlantic probably reflect the intensity of surveying there, particularly in the search for oil. More detailed surveys of other oceans are likely to reveal the existence of further deep-sea reefs.

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DEEP-SEA CORALS

GONIOCORELLA CORAL This deep-sea coral thicket is made mostly of Goniocorella dumosa, a species that is restricted to the Southern Hemisphere. It forms reefs at depths to 5,000 ft (1,500 m). SQUAT LOBSTER This tiny squat lobster is sitting on Madrepora oculata coral polyps, 1,290 ft (390 m) down in the Bay of Biscay, north of Spain. CHIROSTYLUS CRABS Many animals live among the coral. These long-limbed crabs are crawling over a black coral in the northeast Atlantic.

DAMAGED REEF Fishing gear has snagged on this reef west of Ireland, tearing off chunks of living reef that could be up to 8,500 years old. In 2005, the European Union banned fishing near the Darwin Mounds.

TRAWL MARK Even before scientific surveys discovered them, many deep-water reefs had been severely damaged by trawls dragged across the sea bed to catch bottom-living fish. The scarred seabed shown here is at a depth of 2,900 ft (885 m).

OCEAN ENVIRONMENTS

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LOPHELIA REEF This Lophelia reef lies deep in the Atlantic off the west coast of Ireland, where it can be studied only by means of a submersible. Fortunately, Lophelia can also be viewed in water as shallow as 128 ft (39 m) in some Norwegian fjords.

ASSOCIATED MARINE LIFE

Location of Deep-sea Reefs

LIFE IN COLD WATER

THREATS FROM DEEP-SEA TRAWLING

Deep-sea corals were first discovered in 1869, but it took the advent of sonar and deep-sea submersibles to reveal the size and abundance of the reefs that they build. Although less well studied than their tropical counterparts, these cold-water reefs are just as rich in life. The stony corals that form deep-water reefs flourish in water temperatures of 39–55ºF (4–13ºC). Unlike tropical corals, they can live in total darkness because they do not rely on zooxanthellae (p.153) living inside them to produce nourishment by photosynthesis in sunlight. Instead, they survive by filtering food from the water. Some scientists have suggested that there may be a link between the existence of deep-water reefs and the seepage of certain substances, such as methane, from the seafloor. Methane may provide energy for bacteria at the bottom of a food chain, which are then filtered from the water by the coral polyps. One of the biggest areas containing cold-water reefs—covering 38 square miles (100 square km)— was discovered during an oil-related survey of the Atlantic Frontier, northwest of Scotland, in 1998. Lophelia pertusa is the main reef-forming coral at these reefs, which are situated in an area called the Darwin Mounds and lie at a depth of 3,300 ft (1,000 m). Lophelia reefs occur at similar depths on many seamounts in the Atlantic, and also in shallow cold water such as in Norway’s fjords. Several other coral species form cold-water reefs elsewhere in the world. For example, in the Pacific, the main reef species on seamounts and oceanic banks around Tasmania and New Zealand are Goniocorella dumosa and Solenosmilia variabilis. Over 1,300 species of animals have been recorded on deep-sea reefs, and they may be important nursery grounds for commercial fish species.

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THE OPEN OCEAN AND OCEAN FLOOR

Ocean Floor Sediments OVER VAST AREAS OF THE SEABED, THE UNDERLYING

landforms are hidden beneath deep layers of sediments. Made up of silts, muds, or sands that have built up over 200 million years, they now form a blanket that is several miles thick in places. The sediments have various origins. One group, terrigenous sediments, come from land, mainly from fragments of eroded rock that are carried down rivers into the sea, then down the continental slope to form the continental rise and abyssal plain beyond. Other sediments are biogenic, formed from the hard remains of dead animals and plants. A few, called authigenic sediments, are made up of chemicals precipitated from seawater. There are even cosmogenic sediments, which come from outer space as particles in space dust and meteors. All accumulate to form extensive, flat plains. Various animals feed here and burrow into the sediments for shelter.

Deep-sea Sediments

SEDIMENT THICKNESS 0

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MAPPING SEDIMENTS

Ocean sediment depths can be measured and mapped using echosounding. Some areas (white on the map above) are still unsurveyed. Sediment is thickest near land. Glaciers also carry many sediments into the oceans.

OCEAN ENVIRONMENTS

PTEROPOD OOZE Pteropods are small winged snails that float in midwater. When they die, their internal shells of aragonite (calcium carbonate) sink to the seabed, contributing to biogenic oozes. The presence of pteropod remains in samples collected from deep in the ooze reveal changes over millennia in water temperatures and sea levels.

The average thickness of sediments on the ocean floor is 1,500 ft (450 m), but in the Atlantic Ocean and around Antarctica, sediments can be up to 3,300 ft (1,000 m) deep. Closer to the continents—along the continental rise—sediments washed from the land accumulate more rapidly, and can be up to 9 miles (15 km) deep. In the open ocean, further from the source of terrigenous sediments, the buildup rate is very slow: from a fraction of an inch to a few inches in a thousand years. That is slower than the rate at which dust builds up on furniture in an average house. The accumulated sediments tell scientists a great deal about the last 200 million years of Earth’s history. Their form and arrangement provide a vivid snapshot of sea-floor spreading, the evolving varieties of ocean life, alterations in Earth’s magnetic field, and changes in ocean currents and climate. WHITE CLIFFS OF DOVER

These chalk cliffs originated on the sea bed from a biogenic ooze, formed from algal scales (coccoliths) that built up to form layers hundreds of yards thick. They are now raised above sea level.

Sediments Derived from the Land Most terrigenous sediments come from the weathering of rock on land and are swept into the oceans, mainly by rivers but also by glaciers, ice sheets, and wind. Coastal erosion adds to these sediments. Often, they are washed down through submarine canyons to the deeper ocean. Sometimes, the route from land to sea is more indirect: volcanic eruptions eject material into the upper atmosphere before it falls as “rain” into the ocean. In the deepest ocean floors, below about 13,000 ft (4,000 m), the main sediment is red clay, composed mostly of fine-grained silts that have washed off the continents and accumulated incredibly slowly—about 1/32 in or 1 mm per thousand years. These clays may include up to 30 percent of fine, biogenic particles and have four main mineral components—chlorite, DUST STORM illite, kaolinite, and montmorillonite. RESULTS IN SILT Winds from arid regions, Clay types depend on origin and climate. such as North Africa For example, chlorite dominates in polar (shown in this satellite regions, kaolinite in the tropics, and image) carry dust far out montmorillonite is produced by to sea, where it sinks to volcanic activity. form silts.

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OOZE-FORMING ZOOPLANKTON

These radiolarians are single-celled planktonic animals. After death, their skeletons, made of silica glass, sink to the seabed, accumulating as sediments.

Feeding on the Ooze Biogenic Oozes

COCCOLITHOPHORE

When this coccolithophore dies, its platelets will add to the calcareous ooze.

SEA CUCUMBER FEEDING

Sea cucumbers wander widely over the seabed, sucking up the sediment and then extracting its organic content.

FORAMINIFERA

The tiny shells of dead foraminiferans add to the biogenic oozes.

tube feet enable animal to traverse sediment while foraging

OCEAN ENVIRONMENTS

Biogenic sediments are formed mainly from the shells and skeletons of microscopic organisms that sink to the seabed after death. The decaying remains of larger organisms, such as molluscs, corals, calcareous algae, and starfish, add to this accumulation. Oozes are calcareous if derived from the calcium carbonate shells of foraminifera, pteropods, and coccolithophores (microscopic algae), or siliceous if derived from the silica shells of single-celled radiolarians or diatoms. Because silica dissolves rapidly in seawater, siliceous oozes only build up beneath zones of high primary production. As calcareous shells and skeletons sink, they reach a depth (around 15,000 ft/ 4,500 m) where the water becomes more acidic; this, combined with pressure, means calcareous remains are dissolved rapidly in seawater at depth. Calcareous oozes therefore occur only above this “calcium carbonate compensation depth,” beneath which the seabed consists mainly of terrigenous red clays.

The “snow” of calcareous and siliceous remains from the upper levels accumulate on the ocean floor, providing the main source of food for animals living in or on the sediments. Bacteria live in the ooze, where they break down organic remains. In turn, they— along with other organic matter—are consumed by multitudes of tiny foraminiferans. Nematodes, roundworms, isopods, and small bivalve mollusks live and feed in the mud. Brittlestars feed on the ooze by sweeping food off its surface with their arms. Sea pens, crinoids, and glass sponges, which are anchored to the seabed, filter organic particles from the water column.

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THE OPEN OCEAN AND OCEAN FLOOR

Abyssal Plains, Trenches, and Mid-ocean Ridges

mouth barbel

body

OVER VAST AREAS, THE SEABED IS COVERED BY

a flat expanse of accumulated sediments. The sparse life here relies on food falling from above. In places, the abyssal plains are disrupted by more dramatic features, created by tectonic shifts. Where tectonic plates diverge, magma wells up through the gap to create mid-ocean ridges, at which new seabed is constantly being formed. At the other extreme, where plates collide, one plate is dragged downward, opening up a trench.

SEA-BED SCAVENGERS

Hagfish feed on animal corpses that fall to the abyssal plain. Blind and jawless, these primitive fish are attracted by smell. They bore into corpses, using their horny teeth, and secrete clouds of mucus to deter other scavengers.

Abyssal Plains Over large areas of the ocean floor, sediments have built up a blanket several miles thick, obscuring the underlying topography. This produces vast flat or gently undulating abyssal plains at a typical depth of 14,800 ft (4,500 m). These are most common in the Atlantic, where the Sohm Plain alone covers 350,000 square miles (900,000 square km). Abyssal plains lie at different depths, with barriers between them, and this leads to submarine waterfalls, where water spills over the barrier and down into the plain below, at rates of up to 5 mph (8 kph). Occasional abyssal storms also occur, stimulated, in a way not yet fully understood, by instabilities at the ocean surface resulting from atmospheric conditions. Originally thought to be a world without seasons, recent studies have shown that life here responds to pulses of food from above, for instance when the summer bloom of plankton dies and sinks. Most animals in this zone are scavengers with a body temperature close to that of the surrounding water. They move and grow slowly, reproduce infrequently, and live longer than their relatives at the surface.

ABYSSAL FLOOR

OCEAN ENVIRONMENTS

A recent study off the east coast of North America revealed 798 species buried in a small sediment sample from the seabed.

Earth’s outer layer of rock in continental areas is called continental crust

the steep continental slope goes down to about 10,000 ft (3,000 m)

ocean currents carve a deep gorge, called a submarine canyon, in the continental slope the continental shelf is the flooded edge of a continent, which was once dry land

silt carried down a canyon spreads out at the bottom as a fan-shaped deposit

the gently sloping continental rise is a region that extends down from the continental slope

an underwater plateau is a large, flat-topped mound caused by a few million years of underwater volcanic eruptions

MANGANESE NODULE

In places, the abyssal plain is littered with potato-sized nodules of manganese, often contaminated with other valuable metals such as nickel, cooper, and cobalt.

when a volcanic island sinks, it eventually becomes a flat-topped seamount, or “guyot”

direction of plate movement

at the mid-ocean ridge two plates pull apart and magma rises up between them, cooling then solidifying, making a new tectonic plate

each tectonic plate is made of crust and the top layer of the mantle

melted rock is called magma when it occurs beneath Earth’s surface, and lava when it is found above Earth’s surface

ABYSSAL PLAINS, TRENCHES, AND MID-OCEAN RIDGES Mariana Trench

Japan

Ocean Trenches

seamounts

China Pacific Ocean

Ocean trenches are created by a process called subduction. Where oceanic and continental tectonic plates collide, the denser but thinner oceanic plate is forced down beneath the thicker but less dense continental plate, and plunges to its destruction in the mantle deep below. Where two oceanic plates collide, the older plate is subducted beneath the younger. The buckling where the plates collide causes a deep depression at the point of impact—an ocean trench. These are the deepest places on the ocean floor. Trenches are typically V-shaped, with steeper slopes on the continental side. The Pacific is the region of most active subduction, with 17 of the 20 major ocean trench systems. The Atlantic has MARIANA TRENCH two major trenches, the Puerto Rico and South The Mariana Trench is roughly Sandwich trenches, and the Java Trench is the only 1,600 miles (2,500 km) long and 40 miles major trench in the Indian Ocean. The deepest (70 km) wide. It lies in the western trench on Earth is the Mariana Trench, located in Pacific, around 1,000 miles (1,600 km) the Pacific Ocean, near the Mariana Islands. to the south and east of Japan.

Life in the Ocean Trenches

THE DEATH OF A WHALE Occasionally, a dead whale sinks to the abyssal plain and provides a feast. Scientists have counted 12,000 animals of 43 species feeding on the bones of a single whale. It may take them 11

the abyssal plain is a flat expanse of mud that covers a vast area of seafloor

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years to strip the flesh from a blue whale. Later, bacteria invade and decompose the remaining bones. This process leaches out sulfides that sustain a complex community of seafloor life.

volcanic islands form an arc parallel to the ocean trench

each volcanic island is the above-water part of a huge undersea volcano

Animals have been found at great depths in the ocean trenches. The depth record for a fish belongs to a cuskeel, Abyssobrotula galathea. This was dredged in 1970 from a depth of 27,453 ft (8,370 m) in the Puerto Rico Trench. In 1998, the unmanned Japanese submersible Kaiko collected some large amphipods (shrimplike crustaceans) called Hirondellea gigas from the bottom of the Mariana Trench. These were later found to harbor wood-dissolving enzymes in their gut, suggesting they can digest woodfall (tree debris swept into the ocean that eventually sinks to the bottom). Kaiko also collected sediment samples that contained 432 different species of foraminiferans and a range of bacteria. Since 2010, some giant unicellular organisms more than 4 in (10 cm) across, belonging to a class called xenophyophores (a form of foraminiferan), have been observed in the Mariana Trench and elsewhere. Cameras on board the Deepsea Challenger GELATINOUS BLINDFISH that descended to the bottom A small number of these curious fish have been of the Mariana Trench in collected from the seabed in the Atlantic, 2012 detected sea cucumbers Pacific, and Indian Oceans, at depths of at least and a jellyfish as well as 10,000ft (3,000m). Like many deep-water fish, xenophyophores and amphipods. they are almost transparent, with tiny eyes. THE OCEAN FLOOR

oceanic crust is thinner than continental crust, and made of dark-colored rock

the ocean trench forms where one tectonic plate moves under another

magma pools in a chamber beneath a volcano

a volcano forms from a buildup of lava when magma erupts at the surface

DISCOVERY

THE TRIESTE EXPEDITION In 1960, two oceanographers, Don Walsh and Jacques Picard, dived to 35,797 ft (10,911 m) in the Challenger Deep section of the Mariana Trench in the bathyscaphe Trieste—still the greatest depth reached by humans. It took five hours to descend to that depth, and after just 20 minutes hanging there, the crew began their return to the surface.

OCEAN ENVIRONMENTS

The seafloor lies about 2.3 miles (3.7 km) below the sea surface. It is made of a layer of dark-colored rock, called oceanic crust, which is covered in muddy sediment. Tectonic plates are generally made of this oceanic crust and continental crust, along with part of Earth’s deeper mantle layer. Features such as volcanic islands and seamounts are caused by erupting magma.

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THE OPEN OCEAN AND OCEAN FLOOR

The Ring of Fire

SAFE HAVEN

All around the margins of the Pacific Ocean, tectonic plates are colliding. This produces a belt of intense volcanic and earthquake activity encircling the Pacific, known as the Ring of Fire. It extends for 18, 600 miles (30,000 km) in a series of arcs, from New Zealand, through Japan, and down the west coast of the Americas to Patagonia. About threequarters of the Pacific lies over a single plate, the Pacific Plate, which is colliding around its edges with the North American, Australian, and various minor plates. In the eastern Pacific, the smaller Cocos and Nazca plates are colliding with the Caribbean and South American plates. As the edges of the Pacific, Cocos, and Nazca plates subduct (move down) beneath the younger, less dense edges of neighboring plates, massive slabs of rock shatter explosively along faults, producing earthquakes. A series of deep ocean trenches, arranged in arcs around the Ring of Fire, mark the boundaries where the subducting plates move beneath neighbouring plates. Parallel to these trenches—typically at a distance of 100 miles (160 km) and always on the side of the overriding plate—are arcs of often highly active volcanoes, taking either the form of volcanic islands or (on the eastern side of the Pacific) forming lines of volcanoes on land, such as the volcanoes of Central America.

Mid-ocean-ridge islands offer protected breeding places for many sea birds, with rich feeding provided by upwelling currents offshore. The sooty tern is found in all tropical seas. It nests on oceanic islands. Ascension Island once provided safe nesting for 50,000 pairs, until humans introduced rats and cats, more than halving the sooty tern population.

THE RIDGE ON LAND

For most of its vast length, the Mid-Atlantic Ridge is hidden deep beneath the ocean. However, at Iceland, where both the Eurasian and North American plates are separating, it rises above the surface.

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OCEAN ENVIRONMENTS

Red on this map shows areas of volcanic activity around the Pacific Ocean, highlighting the Ring of Fire. These volcanoes form on continental plates as oceanic plates are thrust below.

MOUNT ST. HELENS

Mount St. Helens in Washington is part of the Ring of Fire. It erupted in May 1980, blowing the whole top off the volcano. Here, in 2004, a new lava cone has begun to grow, producing steam.

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Mid–ocean Ridges New sea bed is produced wherever tectonic plates diverge. As plates move apart, they create a rift. Magma wells up through this rift from the Earth’s mantle, forming volcanoes and creating an underwater mountain chain, called a mid-ocean ridge. The lava cools as it meets the seawater, and solidifies in vertical basalt dikes or fields of pillow lava (see p.42). Mid-ocean ridges are assembly lines along which new ocean floor is being produced. The ridges and lava fields remain visible for some time before sediments accumulate over them. Sometimes the volcanoes extend above sea level, producing islands such as Iceland. Some mid-ocean ridges spread slowly, allowing deep rift valleys to form down their centers— others are much faster-spreading but lack rift valleys. Sometimes the ridges are disrupted sideways by transform faults. As the new sea bed spreads outward, tensions are created, making it crack. Water seeps into these cracks and reemerges from hydrothermal vents (see p.188). The oceanic ridge system is the third largest feature on the Earth’s surface, after the oceans and continents.

PILLOW LAVA

Under the high pressure of the deep ocean, lava oozes slowly from the mid-ocean crests. When it meets cold seawater, it cools rapidly to form globular masses, called pillow lavas due to their shape. About 1.4 square miles (3.5 square km) of new sea floor is formed each year along mid-ocean ridges.

ASCENSION ISLAND

Ascension Island arises where the Mid-Atlantic Ridge protrudes above sea level in the south Atlantic. It covers 35 square miles (90 square km) and ascends to 2,817 ft (859 m) on Green Mountain. Sooty terns and sea turtles breed around its shores.

Ridges of the World

OCEAN WANDERERS

Macquarie Island, on the Macquarie Ridge, provides a nesting site for the black-browed albatross. Outside of the breeding season, it wanders the Southern Ocean.

The longest mid-ocean ridge occurs where the Eurasian and African plates are diverging from the North and South American plates. The Mid-Atlantic Ridge runs along this boundary for 10,000 miles (16,000 km), from the Arctic Ocean to beyond the southern tip of Africa, rising 6,000–13,000 ft (2,000–4,000 m) above the sea floor. A chain of volcanoes runs down its length, most famously in Iceland. An eruption close to Iceland in 1963 created a new volcanic island, Surtsey. Ascension Island lies very close to the ridge, and the Azores straddle it, while St. Helena and Tristan da Cunha arise from isolated volcanoes, displaced from it. A valley, 15 miles (25 km) wide, extends along the ridge crest. In the Pacific the main ridge system is the East Pacific Rise. This is Earth’s fastest-spreading system, separating at 5–6 in (13–16 cm) per year. A series of mid-ocean ridges encircle Antarctica, along the divergent boundaries between the Antarctic Plate and its neighbors, and the Carlsberg Ridge runs down the center of the Indian Ocean. Mid-Atlantic Ridge with eastern section displaced by fault in southern part of map

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Atlantis fracture zone

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This section of the Mid-Atlantic Ridge has been displaced by the Atlantis Transform Fault. Transform faults occur where two plates slide sideways against each other.

OCEAN ENVIRONMENTS

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SATELLITE OCEANOGRAPHY

Sensors mounted on satellites use various wavelengths to monitor the Earth’s surface, atmosphere, and oceans, as illustrated in this computer-graphic montage of the Indian Ocean. Visible light, infrared radiation, and microwave data are all processed and projected onto maps that chart the ocean’s physical parameters. Satellites update the maps on a weekly, daily, or hourly basis to monitor ocean dynamics.

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Oceanography from Space FEATURES STUDIED FROM SPACE CLOUDS Cloud cover is detected using visible-light cameras, and cloud-top height data is derived from infrared radiometers on satellites such as Meteosat. These systems are used to track storms and forecast the weather.

RAINFALL The Tropical Rainfall Measuring Mission uses a microwave radiometer to see through clouds and detect the presence of liquid water in the atmosphere. Rainfall measures are used in computer models of the climate and ocean.

WEATHER PLANT LIFE

The world’s oceans are too vast to be adequately studied using ships alone. Even if all of the depth soundings that were taken during the 20th century were to be plotted, the resultant map would provide only sparse information on the sea floor and would even be blank in large areas. The advent of satellite remote sensing in the 1960s brought a revolution in oceanography. For the first time, it was possible to take a picture showing an entire ocean basin. Hurricane tracking and warning was one of the first benefits to accrue from early weather satellites. Eventually, a large range of sensors were developed to probe the physical attributes of the ocean surface and the atmosphere above. Ocean colour and temperature, sea-level height, and surface roughness are among the parameters that can be monitored in some detail. Satellite-derived information is a vital component of practical applications such as weather forecasting, commercial fishing, oil prospecting, and ship routing. In some cases, 30 years of continuous observations have been built up, helping scientists to track seasonal and long-term changes in the ocean environment and understand its effects on the global climate.

CHLOROPHYLL Ocean colour cameras use wavelengths of visible light to measure the concentration of chlorophyll, which is present in phytoplankton. This information is used for water-quality assessment, finding fish, and in various aspects of marine biology. MICROWAVE SCATTEROMETER Surface wind speed and direction are measured by satellites that bounce radio beams off the surface of the ocean. Windinduced ocean waves modify the return signal, and the data can be used for meteorology and climate research.

Satellites cannot directly measure the depth of the sea floor, but it can be derived from the height of the sea surface. The sea is not flat. Water piles up above gravity anomalies caused by ocean-floor features such as seamounts, producing variations in the surface that are much larger than those produced by tides, winds, and currents. By comparing the height of the sea surface against a reference height, the depth of the sea floor can be estimated.

WIND SPEED

Measuring Ocean Depth from Space

satellite orbit

ocean floor

SURFACE TEMPERATURE Infrared radiometers can measure the temperature of the sea surface precisely. Shifts in ocean currents, cold-water upwelling, and ocean fronts can be monitored for ocean and climate research.

signal is bounced from satellite off ocean surface and timed water surface varies according to sea-bed profile

reference surface

dish to track satellite height and to receive data

TEMPERATURE

the longer the signal time the lower the ocean surface

SYNTHETIC APERTURE RADAR Imaging radar systems, such as the one carried by Radarsat, penetrate clouds and can operate through the dark of the extended polar night to monitor ice shelves, sea-ice, and icebergs all year round.

THERMAL GLIDER A new generation of instrument platforms is being developed to sample the vast subsurface volume of the world’s oceans. Autonomous Underwater Vehicles, or “sea gliders”, can undertake long cruises, surfacing every day to return their data via satellite communication links.

OCEAN ENVIRONMENTS

the shorter the signal time the higher the ocean surface

satellite

ICE COVER

JASON-2 SATELLITE Jason-2 carries a radar altimeter, which is similar to the instruments on aircraft that measure their height above the surface of the Earth.

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THE OPEN OCEAN AND OCEAN FLOOR

Vents and Seeps HYDROTHERMAL VENTS ARE SIMILAR

to hot springs on land. Located near ocean ridges and rifts, at an average depth of 7,000 ft (2,100 m), they spew out mineral-rich, superheated seawater. Some have tall chimneys, formed from dissolved minerals that precipitate when the hot vent water meets cold, deepocean water. The mix of heat and chemicals supports animal communities around the vents—the first life known to exist entirely without the energy of sunlight. Elsewhere, slower, cooler emissions of chemicals called hydrocarbons occur from sites known as cold seeps.

DISCOVERY

DISCOVERING WHITE SMOKERS The first hydrothermal vents that scientists observed from Alvin, a submersible, in 1977, were black smokers. Scientists then explored other sites near mid-ocean ridges and found more vent systems. Some looked different: their fluids were white, cooler, and emerged more slowly from shorter chimneys. These were called white smokers (see right).

Hydrothermal Vents

DISTRIBUTION OF VENTS AND RIDGES

Since their discovery in 1977, hydrothermal vents have been found in the Pacific and Indian Oceans, in the mid-Atlantic, and even in the Arctic, always near mid-ocean ridges and rifts.

Hydrothermal vents always form close to mid-ocean ridges and rifts (see p.185), where new ocean crust is forming and spreading, and where magma from the Earth’s mantle lies relatively close to the surface. Seawater seeps into rock cracks opened up by the spreading sea floor. It penetrates several miles into the newly formed crust, close to the hot magma below. This heats the water to 660–750ºF (350–400ºC). The high pressure at these depths stops it from boiling, and it becomes superheated, dissolving minerals from the rocks that it is passing through, including sulfur which forms hydrogen sulfide. The hot water rises back up through cracks and erupts out of the vents as a hot, shimmering haze, complete with its load of minerals.

Black and White Smokers As superheated water erupts from a hydrothermal vent, it meets the colder water of the ocean depths. This causes hydrogen sulfide in the vent water to react with the metals dissolved in it, including iron, copper, and zinc, which then come out of solution in the form of sulfide particles. Sometimes these form pools on the seabed. However, if the water is particularly hot, it spouts up a little before being chilled by the surrounding seawater, and the metal sulfides form a cloud of black, smokelike particles. Some of these minerals form a crust around the “smoke” plumes, building up into chimneys that can reach more than 100 feet in height. Such vents are called black smokers. More recently, a different form of vent has been discovered. In these, 375°C the black sulfides come out of solution as solids well beneath 710°F the sea floor, but other minerals remain in the vent water. Silica and a white mineral called anhydrite form the “smoke” from these chimneys, which, because of their color, are called white smokers. 2°C

OCEAN ENVIRONMENTS

35°F

mineral chimney, which can grow at up to 12 in (30 cm) per day

seepage of seawater down through cracks in the oceanic crust

SMOKING CHIMNEYS

The minerals from black smokers, like this one, can increase the height of a chimney by an incredible 12 in (30 cm) a day. However, the chimneys are fragile, and they collapse when they get too high.

THE FORMATION OF A SMOKER

Water, heated by magma deep beneath the seabed, dissolves minerals from the rocks. When it erupts through vents, the water is chilled by the surrounding sea. This makes minerals precipitate as smoky clouds, which can be white or black; other minerals are deposited to form chimneys.

black cloud of metal sulfide particles

white cloud of silica and anhydrite particles

250°C 480°F shaft or conduit

unique ecosystems, including tube worms, develop in clusters around some smokers

cold water descends through cracks

heated water rises through vents

superheated water reaching temperatures above 750°F (400°C)

hot rock, or magma, heats water that has seeped into crust

VENTS AND SEEPS

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Life Without Sunlight The first biologists to explore hydrothermal vents were amazed at the life they saw. Masses of limpets, shrimps, sea anemones, and tube worms cluster close to the vents, beside unusually large clams and mussels. White crabs and a few fish, such as the eelpout, scrabble among them. Not every vent system is the same: in the Atlantic, there are no tube worms, clams, or mussels, but lots of white shrimps. Some animals that live in darkness depend on sunlit waters for their food supply but vent animals are remarkable in that they do not need sunlight for energy. White mats of bacteria around vents are the key. They oxidize sulfides from the vent water to make energy, and VENT FISH are the vent animals’ food source. This fish, called an eelpout, Some animals have the bacteria feeds on mussels, shrimps, and crabs living around vents. living inside their bodies. GHOSTLY CRAB

The hydrothermal vent crab is one of many vent creatures. Each year, about 35 new species living around vents are being described by scientists.

DIFFERENT ANIMAL COMMUNITIES

Animal communities vary between vent systems. Vents on the MidAtlantic Ridge are inhabited by swarms of rift shrimps (shown here), feeding on sulfide-fixing bacteria, but there are no giant clams.

Cold Seeps

OCEAN SMOKER

This black smoker, seen from Alvin, is similar to the one that scientists first observed in 1977, spewing out dark fluids from deep in the ocean crust.

LIFE ON A SEEP

Mussels containing methane-fixing bacteria live alongside tube worms,soft corals, crabs, and an eelpout at this cold seep, 9,800 ft (3,000 m) down on the seabed near Florida.

WORM WITHOUT A MOUTH The vent tube worm (below) can be 6 ft (2 m) long and as thick as a human arm. It has no apparent way of feeding. However, its body sac contains an organ called a trophosome, filled with grapelike clusters of bacteria. The worm’s crimson plumes collect sulfides from vent water, and the bacteria use these to produce organic material, which the worm absorbs as food.

OCEAN ENVIRONMENTS

The discovery of hydrothermal vents proved that not all deep-sea life depends on sunlight for energy. Soon, other seabed communities were found that could survive in the dark. In the Gulf of Mexico, diverse animal colonies live in shallow waters near where oil companies drill for petroleum. Here, seeps of methane and other hydrocarbons (compounds containing carbon and hydrogen) ooze up from rocks beneath the sea. Mats of bacteria feed on these cold seeps, providing energy for a food chain that includes soft corals, tube worms, crabs, and fish. Other animal communities in deep-sea trenches off the coasts of Japan and Oregon, US, rely on methane, which is released by tectonic activity. Cold-seep communities may be more common than first thought at depths below 1,800 ft (550 m), although there is often no obvious seepage. Such communities may instead rely on chemical-rich sediments exposed by undersea landslides or currents.

THE TWO POLAR OCEANS are the Arctic

Ocean in the Northern Hemisphere and the Southern Ocean, which surrounds the continent of Antarctica, in the Southern Hemisphere. They differ from other oceans in several respects, not least in the sheer quantity of ice that floats on them. This includes sea ice, which is frozen seawater, and icebergs and ice shelves, which are frozen fresh water. The polar oceans contain fewer temperature layers than other oceans, being uniformly cold, and they have different circulation patterns, which are partly wind-driven but also influenced by such factors as river inflow (in the Arctic Ocean) and sea-ice formation. The edges of the sea ice are biologically productive zones where plankton blooms occur in summer, attracting many fish, birds, and mammals.

P OL A R O C E A N S PENGUINS UNDER THE ICE

These emperor penguins are swimming in a break in the sea ice off the coast of Antarctica. They can dive to 2,000 ft (600 m), staying down for up to 20 minutes.

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192

Ice Shelves AN ICE SHELF IS A HUGE FLOATING

ice platform, formed where a glacier, or group of glaciers, extends from a continental ice sheet over the sea. The landward side of an ice shelf is fixed to the shore, where there is a continuous inflow of ice from glaciers or ice streams that flow down from the ice sheet. At its front edge, there is usually an ice cliff, from which massive chunks of ice break off (calve) periodically, forming icebergs. Ice shelves are almost entirely an Antarctic phenomenon, with only a few small ones in the Arctic.

PEOPLE

SIR JAMES CLARK ROSS The British naval officer Sir James Clark Ross (1800-1862) spent his early adulthood exploring the Arctic. In 1839, he set off to find the south magnetic pole, and on January 11, 1840 reached Antarctica, near the western side of what is now called the Ross Sea. Later, Ross and his crew discovered an ice cliff 165 ft (50 m) high. This was later named the Ross Ice Shelf.

ICE CLIFF

Antarctic Ice Shelves Fimbul Ice Shelf Lazarev Ice Shelf Ekstrom Ice Shelf

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Weddell Sea

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Riiser Larsen Ice Shelf Brunt Ice Shelf

Larsen Ice Shelf

Amery Ice Shelf

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Filchner Ice Shelf Ronne Ice Shelf

George VI Sound Abbot Ice Shelf

West Ice Shelf

A N TA R C T I C A Shackleton Ice Shelf

Ross Ice Shelf Getz Ice Shelf

This massive ice cliff was photographed at

Ice shelves surround about 44 percent of the continent the seaward edge of the Riiser-Larsen Ice In front of it, emperor penguins line of Antarctica and cover an area of some 600,000 square Shelf. up to enter the water at Atka Bay, miles (1.5 million square km). The largest is the Ross on the Weddell Sea. Ice Shelf, also called the Great Ice Barrier, discovered by Sir James Clark Ross (see panel, above). It is as large as mainland France, with an area of about 190,000 square miles (500,000 square km) and is fed by seven different ice streams. The second largest, the Ronne–Filchner Ice Shelf, covers about 160,000 square miles (430,000 square km). About 15 or so other ice shelves are dotted around the edge of the continent. Since 1995, a few of the smaller ice shelves around the Antarctic Peninsula, including parts of the Larsen Ice Shelf, have disintegrated, most probably as a result of ocean warming (see p.487).

Ross Sea ICE-SHELF LOCATIONS

Voyeykov Ice Shelf

Sulzberger Ice Shelf

The two largest ice shelves—the Ross and Ronne–Filchner ice shelves—sit on either side of west Antarctica.

Cook Ice Shelf

OCEAN ENVIRONMENTS

Structure and Behavior Every ice shelf is anchored to the sea floor (ending at a point called the grounding line) and has a front part that floats. The front part is usually 330–3,300 ft (100–1,000 m) thick, though only about one-ninth protrudes above water. The back of an ice shelf is fixed while the front part moves up and down with the tides, creating stresses that can lead to the formation of cracks. Overall, there is a gradual movement of ice from the rear to the front of an ice shelf, from where large tabular icebergs occasionally calve. There is sometimes also a slow upward migration of ice, due to seawater freezing to the bottom of a shelf and the ice on the CALVING SHELF The front part of an ice shelf will upper surface melting and evaporating in sometimes break up and the pieces summer. Even deposits from the sea floor drift off as tabular icebergs. Each under an ice shelf are sometimes brought piece visible here has a surface area of several square miles. to the surface by this mechanism.

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GAINS AND LOSSES

An ice shelf gains ice from glaciers flowing into its landward end, from new snowfall, and from seawater freezing to its undersurface. It loses ice by iceberg calving, by some summer melting of its upper surface and through evaporation, and by melting of part of on its undersurface.

In fl o wf rom

Sea Level 1000m (3280ft)

2000m (6560ft)

Gains in ice Losses of ice

Summer evaporation From ponds on surface

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Tide Cracks

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Floating ice shelf

Sea level rises and falls with tide Grounded ice

Freezing of seawater onto underside of ice shelf Melting of ice at depth Grounding line

ICE SHELVES

Surface and Interior

Beneath the Ice Shelves

The upper surfaces of Antarctic ice shelves are inhospitable places. For most of the year, cold air streams called katabatic winds blow down from the Antarctic Ice Sheet and over the ice shelves. The surface of the ice is not flat, but is shaped by the winds into a series of ridges and troughs, called sastrugi. These are typically covered in a snow blanket. In some areas, the surface is littered with rocks from the input glacier or glaciers, or even with material that has been carried upward from the sea floor by vertical movement. In summer, small ponds form on some ice shelves and provide a home for various types of microscopic organisms. Internally, an ice shelf usually contains some tide-induced cracks and crevasses.

Underneath the Antarctic ice shelves are extensive bodies of water that are some of the least explored regions on Earth. Seawater is thought to circulate constantly here, caused partly by new ice formation underneath and around the ice shelves. As new ice forms, it “rejects” salt, making the surrounding seawater denser. This causes the seawater to sink, and helps drive the circulation. Recent attempts have been made to explore these areas, using robotic submarines to take measurements. Little is known about the organisms that LIFE UNDER THE ICE live here, although in 2005 a community Organisms such as starfish and of clams and bacterial mats was found on worms live in shallow water the sea floor under the Larsen B Ice Shelf around the edge of Antarctica, and possibly under the ice shelves. after it broke up (see p.487).

CAVE INSIDE AN ICE SHELF

In summer, the internal cracks and crevasses in an ice shelf may enlarge to form caves as some of the ice melts.

new ice ice platelets rise as density decreases

low-salinity water

annually reforming fast ice

marine ice is found beneath sea level

ice shelf

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melting zone

SEAWATER CIRCULATION

A continuous circulation of seawater is thought to occur under large ice shelves, driven by sea-ice formation on its undersurface and partial melting at depth.

high-salinity water grounding line ice pump driven by salt rejection

OCEAN ENVIRONMENTS

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POLAR OCEANS

Icebergs

ICEBERGS ARE HUGE, FLOATING

OCEAN ENVIRONMENTS

chunks of ice that have broken off, or been calved, from the edges of large glaciers and ice shelves. These chunks range from car-sized objects to vast slabs of ice that are bigger than some countries. It is estimated that each year 40,000 to 50,000 substantial icebergs are calved from the glaciers of Greenland. A smaller number of gigantic icebergs break off the ice shelves around Antarctica. Surface currents carry icebergs away from their points of origin into the open ocean, where they drift and slowly melt. They can last for years and are a considerable danger to shipping.

Sizes and Colors Icebergs include pieces of ice that are hundreds of square miles in area, down to ones the size of houses (bergy bits) or cars (growlers). Tabular icebergs may rise to a height of up to 200 ft (60 m) above the sea surface and extend underwater to a depth of up to 1,000 ft (300 m). Most icebergs appear white because of the light-reflecting properties of air bubbles trapped in the ice. Those made of dense, bubble-free ice absorb all but the shortest (blue) light wavelengths and so have a vivid blue tint. Occasionally, icebergs roll over and expose a previously submerged section to view, which appears aqua green because of algae growing in the ice.

Iceberg Properties

ICEBERG PROPORTIONS

Because pure ice is 90 percent as dense as seawater, an iceberg made entirely of ice will have only 10 percent of its mass visible above water.

Icebergs consist principally of frozen fresh water, with no salt content. This is because they originate not from seawater but from glaciers or ice shelves (floating glaciers), and glaciers themselves come from compacted snow. Typically, an iceberg has a temperature of about -4 to 5˚F (-15 to -20˚C) at its core and 32˚F (0˚C) at its surface. In addition to ice, some icebergs contain rock debris. This is material that has fallen onto the parent glacier from surrounding mountains, or frozen to the glacier’s edges, and eventually becomes incorporated into the ice. An iceberg’s rock load affects its buoyancy. An iceberg with a high rock content may float up to 93 percent submerged.

RANGE OF SHAPES

Icebergs come in a range of shapes including tabular (flat-topped), domed, pinnacled or pyramidal, wedge-shaped, and various irregular shapes, as shown here. TABULAR

PINNACLED

IRREGULAR

DOMED

ICEBERGS

North Atlantic Icebergs

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HUMAN IMPACT

ICEBERG DETECTION

Most icebergs seen in the north Atlantic begin as snow falling on Greenland. This snow eventually becomes ice, which over thousands of years is transported from the Greenland ice sheet down to the sea as glaciers. Icebergs calved from ARCTIC OCEAN the glaciers on the west coast of Greenland (and many from Ellesmere Greenland Island G the east coast) move into Baffin Sea R E Bay. The Labrador Current E N carries these icebergs southeast, ICELAND Humboldt past Newfoundland, into the Hayes north Atlantic. There, most of the icebergs rapidly melt, Baffin Jakobshavn but a few reach as far south as Bay 40˚N—around the same latitude as New York and Lisbon. Arctic circle

Because of their threat to shipping, north Atlantic icebergs are monitored by the US Coast Guard. Information on iceberg sightings, obtained by aircraft and ships, is fed into a computer along with ocean-current and wind data. The future movements of the icebergs are then predicted so that ships can be warned. The southernmost iceberg ever spotted in the Atlantic was only 155 miles (250 km) from Bermuda at 32˚N.

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These massive icebergs were calved from Breidamerkurjökull, a glacier in Iceland, and form a surreal tourist attraction, drifting in the glacial lagoon.

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All Southern Ocean icebergs have ANTARCTICA broken off one of the ice shelves that Minimum extent of surround Antarctica (see p.192). Most sea ice start off as extremely large, tabular e eb icebergs—satellite monitoring of their of Ic Maximum Limit extent of drift tracks has provided useful information C L E A sea ice RA about Southern Ocean currents. After N ST U A calving, these icebergs drift westward around Antarctica in a coastal current (the East Wind Drift). A few are carried in an eastward direction by DISTRIBUTION the Antarctic Circumpolar Current. In extreme cases, The approximate limit of they drift further, reaching as far north as 42˚S in the iceberg drift from Antarctica is shown by the red dotted Atlantic Ocean. The largest Southern Ocean iceberg line. Most Southern Ocean ever recorded measured 183 miles (295 km) long icebergs remain close to the and 23 miles (37 km) wide. Antarctic Circle at 67˚S.

Icebergs that contain rock debris gradually release this material as they melt, and the debris sinks to the sea floor. Thus rock fragments DIRTY ICEBERG can be transported from The fact that this iceberg contains considerable Greenland, for example, amounts of rock and dust is plain from its to the bottom of the “dirty” appearance. This rock will end up north Atlantic. The on the sea floor as ice-rafted material. process is called ice rafting. By examining sediment samples taken from the ocean floor, scientists can often identify rock fragments that have been transported in this way. Such studies can provide clues about past patterns of iceberg calving and iceberg distribution. For example, they have shown that there were short cold periods during the last ice age, called Heinrich Events, when vast armadas of icebergs were calved and crossed the Atlantic eastward from the coast of Labrador.

OCEAN ENVIRONMENTS

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Southern Ocean Icebergs

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Most north Atlantic icebergs are calved by glaciers in west Greenland, such as the Jakobshavn and Hayes glaciers.

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ORIGINS AND DISTRIBUTION

NORTH ATLANTIC OCEAN

WRECK OF THE TITANIC

The Titanic’s bow section, of which the upper deck and railings are seen here, is mostly intact, although deeply embedded in the seafloor.

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The Titanic Disaster THE HISTORY OF THE TITANIC

SETTING SAIL

LEAVING SOUTHAMPTON At the time of its launch, the Titanic was the world’s largest passenger liner and also the most opulent. When the ship left Southampton docks on April 10, 1912, it was carrying about 900 crew and 1,300 passengers, including some of the world’s richest and most prominent people.

MEDIA SENSATION The sinking of the Titanic caused shock around the world. This Chicago newspaper dates from April 16, 1912.

DISASTER

The sinking of the ocean liner Titanic on April 15, 1912, in the north Atlantic ranks as one of the worst peacetime maritime disasters in history. It is also arguably the most famous sinking of all time, partly because the ship had been considered unsinkable. A total of more than 1,500 people died in the disaster, while just over 700 survived. The exact sequence of blunders by which the Titanic came to collide with an iceberg has never been fully explained. It is known that during the 12 hours preceding the disaster, messages were sent from other ships that large icebergs lay in the Titanic’s path. However, these messages may not have reached the ship’s bridge. When the collision occurred, the iceberg did not hit the Titanic head-on, but brushed the starboard side. However, this was enough to buckle the hull and dislodge rivets below the waterline, creating leaks into five of the ship’s hull compartments. Although lifeboats were deployed, there were not enough to hold everyone. Furthermore, some were launched before they were full. As a result, about 1,500 people were still on the ship when it sank. Most are thought to have died of hypothermia in the ice-cold waters. In 1985, the wreck of the Titanic was located by an American–French team, by means of an underwater vehicle with a video camera and lights attached. A notable discovery was that the ship had split in two before sinking—the bow and stern were found lying 2,000 ft (600 m) apart, facing in opposite directions.

THE UNSINKABLE SINKS In the early morning of April 15, about 2.5 hours after colliding with an iceberg, the Titanic’s stern rose out of the water as the ship sank. BOB BALLARD Along with French scientist Jean-Louis Michel, American oceanographer Bob Ballard led the team that discovered the wreck of the Titanic on September 1, 1985, at a depth of 12,500 ft (3,800 m).

The Titanic left England on April 10, 1912, bound for New York. After crossing the English Channel, the ship took on additional passengers in France, and also stopped in Ireland the next day, before continuing on its journey. Three days later, on April 14, the ship’s captain altered course slightly to the south, possibly in response to iceberg warnings received over the radio. However, at 11:40 pm, lookouts spotted a large iceberg directly in front of the ship. Despite a frantic avoiding maneuver, the Titanic hit the iceberg, and by 2:20 am, the ship had sunk.

LIFEBOAT WINDLASS This piece of deck machinery was barely recognizable under a covering of rusticles (nodules containing a mixture of iron compounds and microbes that feed on wrought iron). BANKNOTES Banknotes in surprisingly good condition have been retrieved, including this $5 bill found in the purser’s bag.

departs Southampton 10th April

CANADA

Queenstown

sinks 15th April

New York ATLANTIC OCEAN

ARTIFACTS

Cherbourg

CHINA DISHES Rows of dishes were found lying on the seafloor. Such diverse items as books, watches, and wireless messages have also been retrieved, along with a bronze cherub and hundreds of other objects.

OCEAN ENVIRONMENTS

WAS THIS THE ICEBERG? This photograph, taken six days later in the vicinity of the disaster, shows an iceberg that closely accorded with descriptions provided by survivors.

DISCOVERY OF THE WRECK

First and Last Voyage

198

POLAR OCEANS

Sea Ice

TESTING THE ICE

SEA ICE IS SEAWATER THAT HAS FROZEN

at the ocean surface and floats on the liquid seawater underneath. It includes pack ice—ice that is not attached to the shoreline and drifts with wind and currents—and fast ice, which is frozen to a coast. Sea-ice formation and melting influences the large-scale circulation of water in the oceans. It has important stabilizing effects on the world’s climate, since it helps control the movement of heat energy between the polar oceans and atmosphere. Sea ice strongly reflects solar radiation, so in summer it reduces heating of the polar oceans. In winter, it acts as an insulator, reducing heat loss. Today, scientists are concerned about shrinking sea ice in the Arctic because of its possible effects on climate and wildlife.

Pancake ice, consisting of ice platelets, can be up to 4 in (10 cm) thick. Waves and wind have caused these platelets to collide, hence their curled-up edges.

Formation Seawater starts to freeze when it reaches a temperature of 28.8˚F (-1.8˚C), slightly cooler than the freezing point of fresh water. Sea-ice formation starts with the appearance of tiny needlelike ice crystals (frazil ice) in the water. Salt in seawater cannot be incorporated into ice, and the crystals expel salt. The developing sea ice gradually turns into a thick slush and then, under typical wave conditions, into a mosaic of ice platelets called pancake ice. Subsequently, it consolidates into a thick, solid sheet, through processes such as “rafting” (in which the ice fractures and one piece overrides another) and “ridging” (where lines of broken ice are forced up by pressure). Where ridging occurs, each ridge has a corresponding structure, a keel, that forms on the underside of the ice. Newly formed, compacted sheet ice is called first-year ice and may be up to 12 in (30 cm) thick. It continues to thicken through the winter. Any ice that remains through to the next winter is called multi-year ice.

OCEAN ENVIRONMENTS

HOW ICE FORMS

The stages of sea ice formation vary according to whether the sea surface is calm or affected by waves. A typical sequence in an area of moderate wave action is shown below.

GREASE ICE

PANCAKE ICE

FIRST-YEAR ICE

MULTI-YEAR ICE

Fine ice spicules, called frazils, appear in the water. These coagulate into a viscous soup of ice crystals, called grease ice.

Wave action causes the grease ice to break into slushy balls of ice, called shuga. These clump into platter shapes called pancakes.

The ice pancakes congeal, consolidate, and thicken through processes such as rafting and ridging to form a continuous sheet of ice.

Further thickening, for a year or more, produces multi-year ice. This has a rough surface and may be several yards thick.

SEA ICE

Extent and Thickness

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DISCOVERY

c le

The extent of sea ice in the polar oceans varies over an annual cycle. About 85 percent of the winter ice that forms in the Southern Ocean melts in summer, and on average this ice only reaches a thickness of a yard or two. In the Arctic, some of the ice lasts for several seasons, and this multi-year ice attains a greater thickness—on average 7–10 ft (2–3 m). In winter, pack ice covers most of the Arctic Ocean. In summer, it shrinks in area by more than two-thirds. In recent years, the summer retreat has been more pronounced, raising fears that summer ice coverage Arct may disappear altogether ic C ir by 2050 or earlier.

USS NAUTILUS In 1958, a US submarine, the USS Nautilus, crossed the Arctic Ocean underneath its cover of sea ice, passing the North Pole on August 3. The crossing proved that there is no sizable land mass in the middle of the Arctic Ocean. The submarine traversed the Arctic from the Beaufort Sea to the Greenland Sea in four days at a depth of about 500 ft (150 m).

ARCTIC SEA ICE COVERAGE

ARCTIC OCEAN

Coverage varies from a winter high of 6 million square miles (15 million square km) to a summer low of less than 1.75 million square miles (4.5 million square km). year-round ice winter sea ice

Gaps in the Ice

ICE LEAD

An ice lead forms when an area of sea ice shears. Stresses from winds and water currents are thought to be the cause. Here, a group of beluga whales swims along a lead.

Even in parts of the polar oceans that are more or less permanently ice-covered, gaps and breaks sometimes appear or persist in the ice. These openings vary greatly in size and extent and have different names. Fractures are extremely narrow ruptures that are usually not navigable by boats of any size. An ice lead is a long, straight, narrow passageway that opens up spontaneously in sea ice, making it navigable by surface vessels and some marine mammals. Polynyas are persistent regions of open water, up to a few hundred square miles in area and often roughly circular in shape. They sometimes develop where there is upwelling of warmer water in a localized area, or near coasts where the wind blows new sea ice away from the shore as it forms. ANTARCTIC KRILL

Life Around the Ice

ICEBREAKERS Icebreakers are ships designed for moving through ice-covered environments. An icebreaker has a reinforced hull and a bow shape that causes the ship to ride over sea ice and crush it as it moves forward. The shape of the vessel clears ice debris to the sides and under the hull, allowing steady progress. The most powerful modern icebreaker can advance through sea-ice up to 9 ft (2.8 m) thick.

WEDDELL SEAL

The Weddell seal, found only in the Antarctic, is one of nine seal species that inhabit polar oceans. Weddell seals never stray far from sea ice.

OCEAN ENVIRONMENTS

HUMAN IMPACT

These crustaceans form an important

part of the food chain in the Southern Life thrives around sea ice. One reason for this is that as ice forms, Ocean, where they congregate in salt is expelled into the seawater, causing it to become denser and dense masses. sink. This forces nutrient-laden water to the surface. In summer, the combination of nutrients and sunlight encourages the growth of phytoplankton, which provide a rich food source. These organisms form the base of a food chain for fish, mammals, and birds. In the Arctic, sea ice provides a resting and birthing place for seals and walruses and a hunting and breeding ground for polar bears and Arctic foxes. In the Antarctic, it supports seals and penguins. Breaks in the ice are vital to this wildlife. Seals, penguins, and whales rely on them for access to the air, while polar bears hunt near them. Decreases in Arctic sea ice would drastically shrink some habitats, pushing them toward extinction.

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POLAR OCEANS

Polar Ocean Circulation THE ARCTIC AND SOUTHERN OCEANS

each have their own unique patterns of water flow, which link in with the rest of the global ocean circulation. These flows are driven partly by wind and partly by various factors that influence the temperature and salinity of the surface waters in these oceans—including seasonal variations in air temperature and sea ice coverage, and large inflows of fresh water from rivers. Although driven by similar influences, the significantly different water-flow patterns of these two oceans are largely due to the fact that the Arctic Ocean is encircled by land, whereas the Southern Ocean surrounds a frozen continent.

Arctic Surface Circulation The upper 170 ft (50 m) of the Arctic Ocean is affected by currents that keep it in constant motion. There are two main components to this circulation (see p.424–25). In a large area north of Alaska, there is a slow, circular motion of water called the Beaufort Gyre. This clockwise movement is wind-generated and completes one rotation every four years. The second component, the Transpolar Current, is driven by a vast quantity of water discharged into the Arctic Ocean from Siberian rivers.

MOUTH OF THE LENA RIVER

OCEAN ENVIRONMENTS

The Lena flows across Siberia and discharges 100 cubic miles (420 cubic km) of water into the Arctic Ocean every year.

CIRCULATION AND FEEDING

The Southern Ocean meets warmer water at the Antarctic Convergence, creating a biologically rich feeding area for whales, including these humpbacks.

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Arctic Deep-water Circulation

MISTY SEAS

In the deeper waters of the Arctic, there is a slow circulation of cold, dense water. This circulation is restricted by the structure of the Arctic Ocean, which consists of a central deep basin (the Arctic Basin), bisected by several underwater ridges and surrounded on most sides by shallow continental shelf. Only on the Atlantic side is there a connection between the deep waters of the Arctic and deep ocean waters to the south. On the opposite side, the connection with the Pacific is via the shallow and narrow Bering Strait. What little circulation of water occurs in the Arctic Basin mostly involves influxes of Atlantic water at various depths to the north of Russia, and outflows around Greenland.

PA

C

ARCTIC BASIN CIRCULATION

IF

IC

OC

E

AN

tic Circle Bering Arc Strait ARCTIC OCEAN

Atlantic water enters to the north of Russia and Pacific water via the Bering Strait. As it cools, some of the Atlantic water becomes denser and dips far below the sea ice cover, where it flows around slowly. The main outflow is to the east of Greenland.

The seas around the Antarctic Convergence are prone to mists. Here, a cruise liner approaches a channel just south of the Convergence.

The Antarctic Convergence The Antarctic Convergence is a region of the Southern Ocean encircling Antarctica, located roughly at latitude 55˚S (but deviating from this in places), where cold, northward-flowing waters from Antarctica sink beneath the relatively warmer waters to the north. At the Convergence, there is a sudden change in surface ocean temperature of 5–9˚F (3–5˚C) as well as alterations in the chemical composition of seawater. As a result, the Convergence forms a barrier to the movement of animal species, and the groups of marine animals found on either side of it are quite different. This is a turbulent area. The meeting of different water masses brings dissolved nutrients from the sea bed to the ocean surface. This acts as a fertilizer, encouraging the growth of plankton during the Southern Hemisphere summer. PHYTOPLANKTON

atlantic water pacific water

In summer, massive blooms of phytoplankton occur around the Antarctic Convergence, forming the base of a productive food chain.

Southern Ocean Circulation

AT L A N T I C OCEAN

ALBATROSSES

These black-browed and gray-headed albatrosses inhabit the biologically productive Southern Ocean.

In the Southern Ocean, surface waters move under the influence of two wind-driven currents. Off the coast of Antarctica, the Antarctic Coastal Current carries water from east to west around Antarctica. Several hundred miles north, the Antarctic Circumpolar Current (ACC) moves water in the opposite direction, from west to east, and pushes the Antarctic waters northward. The ACC is a major ocean current that connects the Pacific, Atlantic, and Indian oceans and isolates Antarctica from the warmer ocean currents to the north. In the Southern Ocean, an important movement of water also occurs deep down. In an area near Antarctica, masses of dense, salty water form as salt is rejected from seawater as it freezes. This cold water sinks and moves north into the southern Atlantic.

FRIDJTOF NANSEN The Norwegian explorer and scientist Fridjtof Nansen (1861–1930) is most famous for his Arctic voyage of 1893–1895 on a specially built wooden ship called the Fram. Nansen deliberately allowed the Fram to drift across the Arctic Ocean locked in ice, and in doing so proved the existence of the surface current now called the Transpolar Current. In 1895, setting off with one companion from the Fram, Nansen walked and skied to within 400 miles (640 km) of the North Pole, closer than anyone else up to that time.

OCEAN ENVIRONMENTS

PEOPLE

OCEAN LIFE

BY FAR THE LARGEST HABITAT on Earth,

the oceans are more accurately seen as a great range of environments as disparate as mangrove swamps and deep-sea vents. Living organisms have found a place to take hold in every ocean environment, even the deepest trenches, more than 6 miles (10 km) beneath the surface. Ocean life teems with greatest abundance and variety in the sunlit surface waters. Here, microscopic plants and plantlike organisms, the phytoplankton, fuel productive communities of organisms right up to top predators, such as killer whales. Life began in the oceans, and they were the site of many groundbreaking steps in evolution. Tracing the history of this evolution puts into context the astonishing variety of today’s marine life.

IN TR OD U C TI ON TO O C E A N L IF E KELP FOREST COMMUNITY

Ocean life develops into one of a number of characteristic communities, according to physical conditions. Here in cool, shallow water, a canopy of kelp towers above an undergrowth of encrusting red seaweed, while an eagle ray and smaller fish find shelter among the kelp fronds.

206

INTRODUCTION TO OCEAN LIFE

Classification BY CLASSIFYING ORGANISMS AND FITTING

them into a universally accepted framework, scientists have created a massive reference system that accommodates all forms of life. Over 2 million organisms have been described, of which about 16 percent live in the oceans. The marine proportion is likely to increase because many new species continue to be discovered annually, particularly in the deep ocean.

WHAT IS A SPECIES? A species is the basic unit of classification. One commonly accepted definition of a species is a group of living organisms that have so many features in common that they can interbreed and exchange genes in natural conditions. This definition cannot be applied to fossil species. It also does not work for Bacteria and Archaea and there can be no one universal definition. Other factors such as geographical isolation and DNA (see below) are also important.

LINNAEAN HIERARCHY

Principles of Classification

Linnaeus used a hierarchy of ranked categories of increasing exclusiveness. Today’s expanded system includes many ranks, from domain down to species. Below is an example of a series of ranked categories, illustrating those that classify the common dolphin.

Classification helps us make sense of the natural world by grouping organisms on the basis of features that they share. It gives scientists a clear and accurate understanding of the diversity of life, and because everyone uses the same system, the knowledge is accessible on a worldwide basis. The hierarchical system devised by the Swedish scientist Carolus Linnaeus (see panel, left) in the 18th century still forms the basis of today’s classification. Each species is identified with a unique two-part scientific name (made up of the genus and species names), then categorized in a series of ever-larger groupings. However, as our knowledge increases, it is often necessary to revise the groups. Sometimes, this leads to subdivision of categories, for example phylum Arthropoda has been split into four subphyla. Many new species are discovered each year but describing and publishing them is laborious and time-consuming.

DOMAIN Eucarya Includes all Eukaryotes—organisms that have complex cells with distinct nuclei. Only bacteria and archaea fall outside this domain. KINGDOM Animalia Includes all animals—multicellular eukaryotes that need to eat food for energy. All animals are mobile for at least part of their lives. PHYLUM Chordata Includes all chordates—animals possessing a notochord. In most cases, the notochord is replaced before birth by the backbone. CLASS Mammalia Includes all mammals—air-breathing chordates that feed their young on milk. The jaw is made up of a single bone. ORDER Cetartiodactyla Includes all cetaceans (whales and dolphins)— marine mammals that have a tail with boneless, horizontal flukes for propulsion. FAMILY Delphinidae Includes all dolphins (a subgroup of toothed cetaceans) with beaks and 50–100 vertebrae. The skull lacks a crest. GENUS Delphinus Includes a few colorful, oceanic dolphins with 40–50 teeth on each side of the jaw. These dolphins form large social groups. SPECIES Delphinus delphis Specifies a single type of dolphin with a V-shaped black cape under the dorsal fin and criss-cross hour-glass patterning on its sides.

The Evidence In the past, scientists could identify and classify organisms only by studying anatomy, by looking at form, function, and embryological development (animals only), and by examining the fossil record. Recently, scientists have also been able to investigate organisms by looking at their proteins and their DNA. DNA is a DETAILED ANATOMY complex molecule whose sequential By making a detailed structure is unique to each organism. anatomical examination of material in museum The relatedness of organisms can collections, scientists be determined by comparing these can distinguish between DNA molecules for shared features. similar organisms and This molecular evidence has led to classify them according to shared characters. many revisions of classification. ANIMALS WITH A SKULL A skull is a derived character that unites all the organisms below. The skull is said to have evolved in their common ancestor.

OCEAN LIFE

Cladistics JAWED VERTEBRATES By the 1950s, although most people used the same system of Animals beyond this point form a clade of classification, the criteria they used for placing organisms in organisms with jaws, again assumed to have categories were often neither measurable nor repeatable. been inherited from a common ancestor. The idea emerged to analyze many characters using an automatic, computer-like process, not only to classify BONY VERTEBRATES organisms, but also to trace their evolution. All animals beyond this point form a clade This process became known as cladistics, possessing an inherited bony skeleton, not shared by sharks, lampreys, or hagfish. and it is a widely used technique today. LAMPREY A cladistic analysis examines a wide selection HAGFISH FISH CLADOGRAM of characters shared by a study group of RAY-FINNED FISH This simplified Below is a clade of fish with fins organisms. It finds the most likely pattern of cladogram indicates made up of radiating bones only, evolutionary changes that link the organisms, just three of the steps without the limblike lobes of used to classify fish. involving the least number of steps (evolutionary lobe-fins, or limbs of tetrapods. CARTILAGINOUS FISH Clades include all the branching points). It then arranges the organisms descendants of a common in a tree diagram (cladogram) that reflects their ancestor, so some new groups, such relationships. A cladogram is made up of nested as “lobe-finned fish and tetrapods” groups called clades. A clade encompasses all result, since all tetrapods (land LOBE-FINNED FISH RAY-FINNED FISH the descendants of the group’s common ancestor. vertebrates) descend from lobe-fins. AND TETRAPODS

CLASSIFICATION although the numbers of classes and species cited include all organisms within the group whether they are marine or not. Some groupings, such as fish, are shown in dotted lines because although they are useful categories, they are not true taxonomic groups. Others, such as bottomliving phyla and planktonic phyla, are ecological groupings and do not reflect taxonomy or evolutionary history.

Marine Life THE CLASSIFICATION FRAMEWORK USED in this book is shown on the following three pages. In this framework, all living things are divided into three domains. Within domains, only the marine groups are shown,

BACTERIA DOMAIN

Bacteria

PHYLA

ARCHAEA About 80

SPECIES

Many millions

DOMAIN

Archaea

PHYLA

EUKARYOTES THIS DOMAIN INCLUDES ALL ORGANISMS

that have cells with a nucleus and other complex structures not seen in prokaryotes (bacteria, archaea). The eukaryotes comprise protists, chromists, plants, fungi, and animals.

EUKARYOTES 2

SPECIES

Probably millions

DOMAIN

Eucarya

GREEN SEAWEEDS CLASS

Ulvophyceae

ORDERS

Dinoflagellates Myzozoa

INFRAPHYLUM

CLASSES

4

SPECIES

2,436

About 10

SPECIES

8,699

CLASSES

3

SPECIES

4,000

Foraminiferans CLASSES

3–5

SPECIES

6,616

CLASSES

2

SPECIES

CLASSES

8

SPECIES

260,684

SUPERCLASS

Angiospermae

ORDERS

30

SPECIES

260,000

Fungi Fungi

PHYLA

5

SPECIES

46,574

KINGDOM

Animalia

PHYLA

About 30

SPECIES

Over 1.5 million

progresses from organisms with simple body plans and systems, such as sponges, to the most complex phylum, chordates (pp.208–209), which contains humans. Each phylum represents a distinct body plan.

Porifera

CLASSES

4

SPECIES

About 8,700

CLASSES

5

SPECIES

10,886

ORDERS

10

SPECIES

7,095

ORDERS

3

SPECIES

186

ORDERS

2

SPECIES

41

ORDERS

7

SPECIES

3,516

SPECIES

48

258

CNIDARIANS

Ochrophyta

PHYLUM

Ochrophyta

CLASSES

20

ORDERS

12

SPECIES

100,000

ORDERS

4

SPECIES

490

ORDERS

23

SPECIES

2,053

DIATOMS

SPECIES

5,006

Phaeophyceae

Cubozoa

HYDROIDS CLASS

+ SEVERAL MORE PHYLA

Scyphozoa

BOX JELLYFISH CLASS

BROWN SEAWEEDS

Anthozoa

JELLYFISH CLASS

Chrysophyceae

Cnidaria

CORALS AND ANEMONES CLASS

Bacillariophyceae

GOLDEN YELLOW ALGAE

CLASS

13,365

FLOWERING PLANTS

PHYLUM

Haptophyta

CLASS

SPECIES

SPONGES

Coccolithophorids

CLASS

3

THE FOLLOWING LIST OF ANIMAL PHYLA

Foraminifera

PHYLUM

1,500

Animals

Radiozoa

PHYLUM

Trachaeophyta

DIVISION

KINGDOM CLASSES

Radiolarians

PHYLUM

SPECIES

2 million

+ THREE NON-MARINE DIVISIONS

Dinoflagellata

Ciliophora

PHYLUM

SPECIES

+ SEVEN NON-MARINE CLASSES

Ciliates PHYLUM

8–9

At least 8

CLASSES

VASCULAR PLANTS

is complex, difficult, and constantly in flux. Many important marine plankton groups are collectively referred to as chromists. Others are instead plants or protozoans (kingdom Protozoa).

PHYLUM

Bryophyta

DIVISION

THE CLASSIFICATION OF SINGLE-CELLED ORGANISMS

KINGDOMS

+ SIX MORE CLASSES OF MAINLY MICROSCOPIC GREEN ALGAE

MOSSES

Chromists

207

Hydrozoa

STALKED JELLYFISH CLASS

Staurozoa

ORDERS 1

Plants KINGDOM

Plantae

DIVISIONS

8

SPECIES

315,000

PLANTS COMPRISE EIGHT DIVISIONS, only three of which have truly marine species and are included in this book. Mosses (Bryophyta) are additionally included because a few of them live in the intertidal zone.

DIVISION

Rhodophyta

CLASSES

2 or more

SPECIES

6,394

CLASSES

About 8

SPECIES

5,426

Chlorophyta

SPECIES

200

Prasinophyceae

COMB JELLIES PHYLUM

Ctenophora

CLASSES

2

SPECIES

187

PHYLUM

Chaetognatha

CLASSES

1

SPECIES

131

CLASSES

2

SPECIES

2,014

ROTIFERANS

GREEN ALGAE (MICROSCOPIC) CLASS

with the ocean currents in the plankton and are grouped here on this basis. The Ctenophora and Chaetognatha contain so few species that they are known as minor phyla.

ARROW WORMS

GREEN SEAWEEDS AND ALGAE DIVISION

THE FOLLOWING THREE PHYLA FLOAT

ORDERS

3

PHYLUM

Rotifera

OCEAN LIFE

RED SEAWEEDS

PLANKTONIC PHYLA

208

INTRODUCTION TO OCEAN LIFE

FLATWORMS

CHITONS

Polyplacophora

CLASS

PLATYHELMINTHES PHYLUM

Platyhelminthes

CLASSES

6

SPECIES

20,000

CLASSES

2

SPECIES

430

XENACOELMORPHA PHYLUM

Xenacoelomorpha

Arthropoda

PHYLUM

Nemertea

CLASSES

2

SPECIES

1,358

CLASSES

2

SPECIES

15,000

Annelida

4

CRUSTACEANS

Crustacea

CLASS

Branchiopoda

CLASS

Maxillopoda

CLASS

MEMBERS OF THE FOLLOWING PHYLA all live in or on the ocean floor. The list is not comprehensive—the following phyla are among those not included: Entoprocta, Acanthocephala, Placozoa, and Cephalorhyncha.

SPOON WORMS PHYLUM

Echiura

CLASSES

LAMP SHELLS PHYLUM

Brachiopoda

CLASSES

HORSESHOE WORMS PHYLUM

Phoronida

CLASSES

PEANUT WORMS PHYLUM

Sipuncula

CLASSES

3

SPECIES

900

ORDERS

27

SPECIES

16,589

ORDERS

5

SPECIES

7,462

36,759

ORDERS

Cycliophora

CLASSES

Gastrotricha

CLASSES

Nematoda

2

SPECIES

SPECIES

1

SPECIES

1

SPECIES

CLASSES

2

SPECIES

PRIAPULA WORMS AND MUD DRAGONS PHYLUM

Cephalorhyncha Tardigrada Hemichordata

16

15

SPECIES

FAMILIES

17

SPECIES

480

ISOPODS ORDER Isopoda

FAMILIES

94

SPECIES

11,515

AMPHIPODS ORDER Amphipoda

FAMILI ES

119

SPECIES

10,158

KRILL ORDER Euphausiacea

FAMILIES

2

SPECIES

86

SPECIES

15,000

LOBSTERS, CRABS, AND SHRIMPS ORDER Decapoda FAMILIES 105

147 2 847 20,000

SUBPHYLUM

CLASS

Chelicerata

CLASSES

SPECIES

236

CLASSES

3

SPECIES

1,000

SPECIES

130

3

CLASSES

CAUDOFOVEATES CLASS

Caudofoveata

Solonogasters

Monoplacophora Scaphopoda

73,682

SPECIES

131

ORDERS

4

SPECIES

273

ORDERS

1

SPECIES

30

Merostomata Pycnogonida

SUBPHYLUM

70,000

ORDERS

1

SPECIES

4

ORDERS

1

SPECIES

1,342

Hexapoda

CLASSES

4

SPECIES

About 1.11 million

ORDERS

29

SPECIES

1.1 million

BRYOZOANS PHYLUM

1

SPECIES

571

OCEAN LIFE

Bivalvia

17

SPECIES

ORDERS

16

SPECIES

61,682

ORDERS

9

SPECIES

816

ORDERS

GASTROPODS CLASS

Gastropoda

CEPHALOPODS CLASS

Cephalopoda

9,209

CLASSES

3

Echinodermata

CLASSES

5

SEA LILIES AND FEATHER STARS Crinoidea

SPECIES

6,085

Asteroidea Ophiuroidea

SPECIES

638

ORDERS

8

SPECIES

1,851

ORDERS

2

SPECIES

2,074

ORDERS

16

SPECIES

999

ORDERS

6

SPECIES

1,716

SEA URCHINS CLASS

Echinoidea

SEA CUCUMBERS KINGDOM

Holothuroidea

7,278

4

BRITTLESTARS CLASS

SPECIES

ORDERS

STARFISH CLASS

BIVALVES CLASS

Bryozoa

ECHINODERMS

CLASS

ORDERS

Insecta

+ 1 OTHER NON-MARINE SUBPHYLUM, MILLIPEDES AND CENTIPEDES (MYRIAPODA)

PHYLUM

TUSK SHELLS CLASS

SPECIES

1

MONOPLACOPHORANS CLASS

8

ORDERS

SOLENOGASTRES CLASS

71,004

SPECIES

HEXAPODS

CLASS

MOLLUSKS Mollusca

SPECIES

12

INSECTS

PHYLUM

13

ORDERS

SEA SPIDERS CLASS

CLASSES

Arachnida

HORSESHOE CRABS CLASS

4

PTEROBRANCH WORMS AND ACORN WORMS PHYLUM

393

CLASSES

WATER BEARS PHYLUM

ORDERS

SPIDERS, SCORPIONS, TICKS, AND MITES

ROUND WORMS PHYLUM

1

SPECIES

197

6

MANTIS SHRIMPS ORDER Stomatopoda

CLASS

CHELICERATES

GASTROTRICHS PHYLUM

3

SPECIES

MALACOSTRACANS Malacostraca

About 1.25 million

+ 10 MORE MINOR ORDERS

CYCLIOPHORANS PHYLUM

1

Ostracoda

SPECIES

61,710

MUSSEL SHRIMPS

BOTTOM-LIVING PHYLA

970

SPECIES

SPECIES

CLASSES

BARNACLES AND COPEPODS

SEGMENTED WORMS PHYLUM

SUBPHYLA

WATER FLEAS AND RELATIVES

RIBBON WORMS

3

ARTHROPODS

SUBPHYLUM

PHYLUM

ORDERS

CLASSIFICATION

209

CHORDATES PHYLUM

Chordata

3

SUBPHYLA

SPECIES

64,618

THE VERTEBRATES DOMINATE PHYLUM CHORDATA.

The remaining two, much smaller, subphyla are united with vertebrates by the presence of the rodlike notochord, which becomes the backbone before birth in vertebrates. TUNICATES (SEA SQUIRTS AND RELATIVES) SUBPHYLUM

Tunicata

4

CLASSES

LANCELETS SUBPHYLUM

Cephalochordata

3,026

CLASSES

1

SPECIES

30

CLASSES

10

SPECIES

61,562

VERTEBRATES SUBPHYLUM

SPECIES

CLINGFISH ORDER Gobiesociformes

SPECIES

162

PIPEFISH AND SEAHORSES ORDER Syngnathiformes SPECIES 364

NEEDLEFISH ORDER Beloniformes

SPECIES

266

SCORPIONFISH AND FLATHEADS ORDER Scorpaeniformes SPECIES 1,649

SILVERSIDES ORDER Atheriniformes

SPECIES

344

PERCHLIKE FISH ORDER Perciformes

SPECIES

11,061

SQUIRRELFISH AND RELATIVES ORDER Beryciformes SPECIES 161

FLATFISH ORDER Pleuronectiformes

SPECIES

796

DORIES AND RELATIVES ORDER Zeiformes

PUFFERS AND FILEFISH ORDER Tetraodontiformes

SPECIES

437

SPECIES

33

STICKLEBACKS AND SEAMOTHS ORDER Gasterosteiformes SPECIES 29 + 16 MORE ORDERS

Vertebrata

HAGFISH HAVE AT TIMES

been excluded from the vertebrates because they have only vestiges of a vertebral column. However, recent molecular studies confirm they are related to the other jawless fish, the lampreys. Reptiles, birds, and mammals (as well as amphibians, of which there are no marine species) are informally grouped together as tetrapods (Tetrapoda) within the larger group of jawed vertebrates (Gnathostomata), which also include fish.

REPTILES CLASS

Reptilia

ORDERS

4

SPECIES

7,723

FAMILIES

12

SPECIES

300

FAMILIES

44

SPECIES

7,400

FAMILIES

3

SPECIES

23

TURTLES ORDER

Chelonia

SNAKES AND LIZARDS

Squamata

FISH

ORDER

“FISH” IS AN INFORMAL TERM for four classes of animals. Similarly, “jawless fish,” “cartilaginous fish,” and “bony fish” are informal groupings.

CROCODILES

JAWLESS FISH (AGNATHANS)

Crocodilia

BIRDS

HAGFISH CLASS

ORDER

+ 1 NON-MARINE ORDER: THE TUATARAS (SPHENODONTIDA)

Myxini

LAMPREYS CLASS Cephalaspidomorphi

ORDERS

1

SPECIES

79

ORDERS

1

SPECIES

46

CLASS

Aves

ORDERS

29

SPECIES

9,500

IN THIS CLASSIFICATION, the

birds have been divided into 29 orders. Some scientists consider birds to be grouped within the reptiles. WATERFOWL (DUCKS, GEESE, AND SWANS) ORDER

Anseriformes

FAMILIES

2

SPECIES

177

FAMILIES

1

SPECIES

18

FAMILIES

1

SPECIES

5

FAMILIES

4

SPECIES

142

FAMILIES

1

SPECIES

23

FAMILIES

6

SPECIES

65

FAMILIES

6

SPECIES

119

FAMILIES

5

SPECIES

333

FAMILIES

18

SPECIES

385

FAMILIES

9

SPECIES

230

ORDERS

27

SPECIES

PENGUINS

SHARKS, RAYS, AND CHIMAERAS SHARKS, SKATES, AND RAYS CLASS

Elasmobranchii

ORDER

DIVERS AND LOONS

ORDERS

13

SPECIES

FAMILIES

34

SPECIES

1,241

9

523

Gaviiformes

ORDER

Procellariiformes

GREBES

SKATES AND RAYS ORDERS

ORDER

ALBATROSSES AND PETRELS

SHARKS ORDERS

Sphenisciformes

4

FAMILIES

17

SPECIES

718

ORDER

Podicipediformes

PELICANS AND RELATIVES

CHIMAERAS CLASS

ORDER

Holocephali

ORDERS

1

SPECIES

49

HERONS AND RELATIVES ORDER

ORDER

LOBE-FINNED FISH ORDERS

Actinopterygii

Acipenseriformes

ORDERS

SPECIES

Elopiformes

SPECIES

45

SPECIES

31,282

9

LIGHTFISH AND DRAGONFISH ORDER Stomiiformes SPECIES 426

SPECIES

219

Albuliformes

SPECIES

13

Anguilliformes

SPECIES

908

LANTERNFISH AND RELATIVES ORDER Myctophiformes SPECIES 252

SPECIES

263

Charadriiformes

VELIFERS, TUBE-EYES, RIBBONFISH

HERRINGS AND RELATIVES ORDER Clupeiformes SPECIES 399

COD FISH AND RELATIVES ORDER Gadiformes SPECIES 610

MILKFISH ORDER Gonorhynchiformes

SPECIES

37

TOADFISH AND MIDSHIPMEN ORDER Batrachoidiformes SPECIES 83

CATFISH AND KNIFEFISH ORDER Siluriformes

SPECIES

3,604

CUSK EELS ORDER Ophidiiformes

321

ANGLERFISH ORDER Lophiiformes

SPECIES

ORDER

Lampriformes

ORDER

Coraciiformes

+ 18 NON-MARINE ORDERS

MAMMALS CLASS

Mammalia

5,500

SPECIES

SPECIES

SPECIES

25

mammal orders are listed here. The pinnipeds (seals, sea lions, and walruses), until recently classified as order Pinnipeda, do not form a natural group, and have been placed within order Carnivora (cats, dogs, bears, otters, and relatives). The 27 mammal orders includes new orders formerly classified as marsupials. CARNIVORES ORDER

Carnivora

FAMILIES

9

SPECIES

249

FAMILIES

12

SPECIES

85

FAMILIES

2

SPECIES

4

WHALES AND DOLPHINS

Cetacea

531

ORDER

358

SEA COWS ORDER

Sirenia

+ 23 MORE NON-MARINE ORDERS

OCEAN LIFE

SWALLOWERS AND GULPERS ORDER Saccopharyngiformes SPECIES 28

SMELTS AND RELATIVES ORDER Osmeriformes

ORDER

THREE PARTLY OR WHOLLY MARINE

GRINNERS ORDER Aulopiformes

EELS ORDER

8

SALMONS ORDER Salmoniformes

BONEFISH ORDER

SPECIES

28

TARPONS AND TENPOUNDERS ORDER

3

KINGFISHERS AND RELATIVES

STURGEONS AND PADDLEFISHES ORDER

Falconiformes

WADERS, GULLS, AND AUKS

Sarcopterygii

RAY-FINNED FISH SUBCLASS

Ciconiiformes

BIRDS OF PREY

BONY FISH

SUBCLASS

Pelicaniformes

RED SEA REEF

The Red Sea is one of the world’s top 18 coral hotspots. Its colorful reefs are home to an abundance of marine life, including the venomous red lionfish.

211

Biodiversity Hotspots

Tropical coral reefs are popular with divers because they are colorful, shallow and mostly easy to reach. Both with scientists and with many recreational divers involved in collecting data as part of worldwide projects such as Reef Check, we know far more about life on coral reefs than many other ocean habitats. A study in 2002 pinpointed 18 coral reef hotspots (shown in red below). These sites cover 35 percent of the world’s total coral reef area but are home to more than 60 percent of rare and localized reef species, so they are a high conservation priority. An area called the Coral Triangle (outlined in the map below) stretches from the Philippines in the north, to Malaysia, Indonesia, and Timor Leste in the south and west to Papua New Guinea and the Solomon Islands. This giant hot spot supports 600 species of reef-building corals and more than 2000 species of reef fish. ARCTIC OCEAN

ATLANTIC OCEAN

other coral reef areas

Coral Triangle

HIDDEN HOTSPOT BURIED RICHES

abundance of rare and endemic species

SABA BANK A 2006 survey of this atoll in the Caribbean Netherlands found a high species biodiversity. The area was declared a national park in 2012. NEW TO SCIENCE The Saba Bank study discovered a seven-spined goby living on the seabed. It is a new species, and probably a new genus.

GUADALUPE SEAMOUNT Up to a third of species of seaweed, plants, and animals on isolated seamounts may be unique (or endemic) to that seamount, having evolved there over millions of years.

SAMPLING SEDIMENTS Mud cores collected from the seabed can contain thousands of species of microorganisms. Deepsea sediment was once thought to be like a desert but this hidden biodiversity proves otherwise.

OCEAN LIFE

SOUTHERN OCEAN

BENEATH THE SURFACE Underwater, however, Loch Carron is as full of life as any tropical coral reef. Animals include soft corals, dahlia anemones, and brittlestars.

FISH HAVEN Soldierfish and snappers gather at a seamount in the Indian Ocean. The upwelling of nutrient-rich currents around seamounts makes them “oases” of the ocean.

PACIFIC OCEAN

INDIAN OCEAN

LOCH CARRON The northwest Highlands of Scotland may be scenic, but very little biodiversity is found in the harsh, rocky landscape that surrounds Loch Carron.

CARIBBEAN TREASURE CHEST

Coral Reef Hotspots

TYPES OF HOTSPOTS

SEAMOUNT COMMUNITIES

Many people have heard of biodiversity hotspots, particularly in the context of documentaries about ocean life. These sites are very popular with filmmakers for the variety of life they exhibit. However, the term is a slight misnomer. Strictly speaking, such sites are “species diversity hotspots,” places where the largest number of species are concentrated in a small area. Identifying such hotspots helps conservationists to decide where protected areas should be set up. However, places where species diversity is low, such as the ocean trenches, are also important because of the remarkable animals that live there. The problem is that too little is known about the deep ocean for scientists to be sure where the highest species diversity occurs beyond the shallow layer accessible to human divers. However, worldwide assessments have been made of the distribution and richness of coral reefs (see p.152 and below), seagrass beds (see p.146), and mangrove swamps (see p.130). Hot spots where there are many different species of sea turtles, sharks, and open-ocean fish have been found near islands, sea mounts, and shelf breaks. A major tenyear project called the World Ocean Census, completed in 2010, collected a huge amount of new data on where species live in the ocean. Many thousands of new species were documented, and the work of describing these is ongoing. Marine scientists from more than 80 countries took part, and many new hot spots were found, including several important sea mounts.

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INTRODUCTION TO OCEAN LIFE

Cycles of Life and Energy ALL LIFE DEPENDS ON ORGANISMS

that harness energy from either chemicals or the Sun to produce food. These organisms, whether phytoplankton, seaweeds, or bacteria, are called primary producers and form the first link of a food chain. This first link is just one point in a cycle that processes chemical energy and nutrients through the entire community of life in an ecosystem, into the physical environment, and back again.

Energy Flow As each organism in an ecosystem is eaten in turn by the next organism in the food chain, food energy flows from prey to consumer. The primary producers—the organisms such as diatoms and bacteria at the beginning of the food chain—are eaten by organisms called primary consumers, which are eaten by secondary consumers, and so on to top predators—animals not preyed upon by anything else. In land-based ecosystems, the total mass of organisms at each succeeding food-chain level decreases, leaving very few top predators. However, in marine ecosystems with phytoplankton as producers, the mass is greatest at the primary consumer level. This is possible because phytoplankton grow so rapidly that they provide great turnover despite having little mass. FOOD-ENERGY PYRAMID

BIOMASS PYRAMID

At each level of a food chain, energy is lost as heat, so less is available to the next consumer. The diminishing energy at each level can be represented by a pyramid (below) and accounts for the scarcity of top predators.

The biomass pyramid (below) for a system with plankton producers is partly inverted, because the producers have low total mass. Despite this, the rapid reproduction of the plankton keeps the food chain supplied.

top predators

top predators

predators

predators

consumers

consumers

primary producers

Recycling All living things need a supply of chemical nutrients, such as nitrates, phosphates, and silicates, to grow and reproduce. They are taken up by primary producers then passed along the food chain. Although some nutrients are available from seawater, most are derived ultimately from the sea floor. When an organism dies, any parts that are not eaten by other animals gradually sink to the sea floor, where they are broken down by bacteria and other decomposers. Fecal matter also ends up on the seabed and is processed by detritus feeders or decomposers. Eventually, the nutrients are released into the environment in their mineral, nonliving forms. They may then remain at depth, or they may be returned to surface waters by circulating water currents within an ocean basin (see upwelling, opposite). upwelling of nutrients released by bacteria

NUTRIENT CYCLE

phytoplankton absorbs sunlight and use nutrients to grow zooplankton feed on phytoplankton

detritus falls

WARM WATER

HUMAN IMPACT

COLD WATER

fish eats detritus

detritus falls to sea floor

primary producers TOTAL BIOMASS

TOTAL ENERGY

PRIMARY PRODUCERS

PRIMARY CONSUMERS

detritus on sea floor

bacteria process detritus

SECONDARY CONSUMERS

TERTIARY CONSUMERS

QUATERNARY CONSUMERS

phytoplankton krill

Small particles of organic matter, or detritus, are found in the water column. They may be eaten by scavengers or broken down still further by bacteria present in the water. However, many of them rain down on the ocean floor where they decompose, releasing nutrients. The nutrient cycle is completed by upwelling water currents that then carry the nutrients back to the surface where they can be utilized by the phytoplankton.

baleen whales

OVER-HARVESTING These fishermen are harvesting Pacific cod. Cod populations have drastically declined and many important stocks have collapsed because too many are being caught for human consumption before they can reproduce successfully. The imposition of quotas by governments has not solved the problem, although numbers are starting to recover in some areas. COD FISHING

More than 1.5 million tons of cod (Atlantic and Pacific) were caught in 2010 using various methods including trawls and longlines.

birds

protozoans

carnivorous zooplankton

penguins

seals

pelagic fish decomposer bacteria

FOOD WEB squid

OCEAN LIFE

copepods

seaweed

decomposer invertebrate

detritus on sea floor

demersal fish

small toothed whales

killer whales

Many food chains have been combined to form this complex food web, extending from primary producers to quaternary consumers (top predators) for a Southern Ocean ecosystem. Each arrow shows the flow of food energy from prey to predator, grazer, or decomposer. It shows how organisms depend on one another for food. Some animals feed on organisms from several different levels of the food chain, adding to its complexity. Food webs are delicately balanced and easily upset by human interference.

CYCLES OF LIFE AND ENERGY

Productivity

Upwelling

Throughout the world’s oceans, the abundance of marine life varies dramatically. The ocean is more productive in some places and at some times than others. The amount of sunlight is a major influence on productivity and changes with latitude and time of year. The supply of nutrient-rich water from the sea floor and light for photosynthesis is affected by changing water movements and day length, affecting plankton levels. Temperature also affects productivity as it influences the rate of photosynthesis.

The open-ocean surface water can become impoverished, as nutrients are constantly absorbed by phytoplankton and fall with detritus to the sea floor. Nutrient-rich water can be restored to the surface on a large scale by vertical ocean currents in a process called upwelling (see p.60). Near land, coastal upwelling is caused by surface currents, such as the Humboldt Current off South America (see p.58). In the equatorial waters of the Pacific and Atlantic, mid-ocean upwelling occurs when water masses are driven north and south by the trade winds, and cooler, nutrient-rich water rises to take their place. Polar upwelling can happen where winter storms cause intense water movement. When upwelling occurs and there is sufficient sunlight, phytoplankton multiply rapidly to support a vast number of organisms, creating the most productive ocean waters in the world.

CLEAR, TROPICAL OCEAN

Tropical waters are not mixed seasonally, so few nutrients are returned to the surface, and little plankton growth is possible. Here, a solitary turtle cruises in crystal-clear surface waters near Hawaii.

RICH, MURKY TEMPERATE SEA

In coastal and temperate areas, water turbulence circulates nutrient-rich water that supports a variety of algae, such as this kelp forest in the Pacific.

213

NUTRIENT-RICH WATERS

Where there is upwelling, large numbers of small fish gather to feed on the plankton. They, in turn, attract larger predators like these copper sharks feeding on sardines off the coast of South Africa.

OCEAN LIFE

214

INTRODUCTION TO OCEAN LIFE

Swimming and Drifting MOST OF THE OCEAN’S LIVING SPACE IS NOT ON THE SEABED

but in the water column and out in the open ocean—areas known as the pelagic zone. Salt water provides support, as well as the nutrients that allow many plants and animals to live in the water column without ever going near the seabed. Some animals live at the interface between ocean and air, or alternate between both environments, because it is more energy-efficient. The water surface, water column, and seabed are all interconnected, and many animals move between these habitats.

Plankton The sunlit, surface layers of the ocean are home to many tiny plants and animals (plankton) that drift with the water currents. Phytoplankton consist of bacteria or plantlike chromists (see p.234) that can photosynthesize and make their own food. Along with fixed seaweeds and seagrasses, phytoplankton form the basis of ocean food webs. Zooplankton consists of animals, most of which are very small and feed on the phytoplankton. However, jellyfish can grow to a huge size. Many deep-sea forms have strange shapes and soft bodies that are very delicate. Some zooplankton, such as arrow worms, comb jellies, and copepods, live permanently in the plankton, hunting and grazing (holoplankton), while others are simply the larval and dispersal stages of animals, including crabs, worms, and cnidarians (meroplankton) that will spend part or all of their adult lives on the seabed. Many planktonic organisms have elegant spines, long legs, or feathery appendages that help them PLANKTONIC LARVA float. Tropical zooplankton generally have more The eggs of the of these than their temperate or polar equivalents common shore crab because warm water tends to be less dense and hatch into floating, spiny zoea larva. viscous, and so provides less support.

TEMPORARY PLANKTON

Most temporary zooplankton are the larvae of animals that, as adults, live on the seabed. The common jellyfish, however, has a planktonic adult stage (shown above), and a fixed, asexual, juvenile stage (right).

Nekton Fish and most other free-living marine animals can all swim, even if only for short distances, over the seabed. However, some animals spend their whole lives swimming in the open ocean and are collectively called nekton. This group includes many fish and all whales, dolphins, and other marine mammals, turtles, sea snakes, and cephalopods. There are also some representatives from other groups such as swimming crabs and shrimp. Most nektonic animals are streamlined, TYPICAL NEKTON FEATURE Dusky dolphins are typical of nektonic and there is a remarkable similarity in animals, most of which are vertebrates shape between some dolphins and open(animals with backbones). ocean nektonic fish such as tuna.

OCEAN LIFE

The Ocean–air Interface Some animals live at the interface between air and water, either floating at the surface or alternating between the two environments. Oceanic birds such as albatrosses, petrels, gannets, and tropic birds spend their whole lives out at sea. They eat, sleep, preen, and even mate on the ocean surface. Large rafts of such seabirds are particularly vulnerable to oil spillages. Other diving seabirds, such as terns, alternate between hunting at sea and resting on land. Just as these birds plunge down into the water to catch fish, so some sharks lunge out of the water to catch birds and turtles. Flying fish launch into the air to escape their predators. Some planktonic animals live permanently at the water surface with part of their body projecting into the air. The by-the-wind sailor is a small, colonial cnidarian that is supported by a sail-like float and transported by wind blowing against its vertical sail. Drifting with it on a raft of mucous DRIFTING AT THE INTERFACE bubbles is the violet sea snail, which also feeds The large gas-filled float of the on it. There are even surface-living insects, of Portuguese man-of-war supports the whole colony at the water surface. the genus Halobates, that drift the oceans.

FLYING AND DIVING

The brown pelican is one of several species that dive or dip down from the air into the water to catch fish. It uses its capacious beak as a scoop.

215

FLOATING COMMUNITY

Ocean sunfish often drift at the ocean’s surface. They will investigate floating rafts of seaweed and logs for potential food such as small fish and crustaceans.

Drifting Homes

LURING FISH Fish-attracting devices (FADs) have increased catches in many areas by making fish stocks easier to exploit. However, they make no contribution to biological productivity because they simply gather fish together, and so may contribute to overexploitation. Artificial reefs also attract fish, but provide safe breeding sites, too.

FISH-ATTRACTING DEVICE

Even simple FADs, such as this floating buoy in Hawaii, will attract fish. Juvenile jacks and endemic Hawaiian damselfish can be seen sheltering under this one.

OCEAN LIFE

Many pelagic fish species are attracted to floating objects that provide shelter from predators, currents, and even sunlight. Floating logs and seaweed also provide a meeting point. Fishermen have exploited this tendency by using fish-attracting devices (FADs, see panel, right) to concentrate fish in one area. These vary from simple rafts with hanging coconut palm leaves to complex technological devices. Mini-ecosystems often develop on and around large drifting logs. Seaweeds and goose barnacles settle, providing shelter and food for crabs, worms, and fish. Shipworms bore into the wood, and their tunnels provide further refuge. Occasionally reptiles, insects, and plant seeds SARGASSO HAVEN survive and drift on logs, Floating Sargassum seaweed and may eventually be provides a safe haven for the washed ashore to colonize sargassumfish. More than new places, including new 50 animal species have been recorded in this habitat. volcanic islands.

HUMAN IMPACT

216

INTRODUCTION TO OCEAN LIFE

Bottom-living ANIMALS LIVING ON THE OCEAN FLOOR

or within its sand and mud, either moving over it or firmly attached, are called benthic animals. On land, plants provide a structural habitat within which animals live. In the ocean, this is rarely the case, except in shallow, sunlit areas dominated by kelp, seaweeds, or seagrasses. Instead, wherever areas of hard sea bed provide a stable foundation, a growth of benthic animals develops, fixed to the sea bed and often resembling plants. A sea bed of shifting sediments is no place for fixed animals. Here, a community of burrowers develops instead. BENEATH THE SEAWEED

Below the seaweed-dominated zone around northern European coasts, on sea beds too deep and dark for photosynthesis, dead man’s fingers, sponges, and tube worms typically grow attached to subtidal rocks.

Fixed Animals Many benthic animals such as sponges, sea squirts, corals, and hydroids spend their entire adult lives fixed to the sea bed, unable to move around. On land, animals must move around in search of food, whether they are grazers, predators, or scavengers. In the ocean, water currents carry an abundant supply of food in the form of plankton and floating dead organic matter. Fixed animals can take advantage of this by simply catching, trapping, or filtering their food directly from the water, without having to move from place to place. When it is time to reproduce, they simply shed eggs and sperm into the water, where the eggs are fertilized and grow into planktonic larvae. Sometimes, they retain their larvae or eggs, and release them REEF-FORMING TUBE WORM In some Scottish sea lochs, the only when the young are well developed. Water currents distribute the offspring to chalky cases of tube worms form substantial reefs. new areas, where they can settle and grow.

Mobile Animals

OCEAN LIFE

Dense growths of seaweeds or fixed animals provide shelter and food for many mobile animals. Grazers, such as sea urchins, crawl through the undergrowth, eating both seaweeds and fixed animals. Meanwhile, crabs, lobsters, and starfish scramble and swim around, hunting and scavenging for food. Sea slugs are specialist predators, each species feeding on one, or a few, types of bryozoans, hydroids, or sponges. Sea slugs therefore live in close association with their prey and rarely stray far. Kelp holdfasts provide a safe haven for small, mobile animals such as worms.

FISH IN DISGUISE

Scorpionfish live on the seabed among the seaweeds and fixed animals. Their intricate skin-flaps blend in with this habitat.

SEABED IN THE SUN

Seaweeds anchor in the tidal zone of rocky shores and on rocky reefs, such as this one in the Canary Islands. On sunlit, temperate sea beds, it is seaweeds that provide the community structure.

BOTTOM-LIVING

217

Burrowing and Boring Much of the seafloor is covered in soft sediments, such as sand and mud. Living on the surface of the sediment is both difficult and dangerous, and most animals burrow below or build tubes in which to live and hide. Bivalve molluscs and segmented worms cope especially well in this habitat, and many different species can be found in sediments all over the world. Safe under the sediment surface, a bivalve draws in oxygen-rich water and plankton through one of its two long siphons, expelling waste through the other. It never has to come out to feed or breathe. Piddocks and shipworms bore into rocks and wood, then use their siphons in a similar way. Sediment is not a completely safe home—predatory moon snails dig through sand and bore into bivalve shells, eating the contents. Ragworms are also active predators, hunting through the sediment for other worms and crustaceans. Some worms build flexible tubes from sand grains, their own secretions, or both. The tubes stick out of the sand, and they feed by extending feathery or sticky tentacles from the tube to catch plankton. If danger threatens, they can withdraw rapidly. A similar strategy is adopted by tube anemones and sea pens.

REPLACING SIPHONS

BORING INTO ROCK

The siphon tops of buried bivalve mollusks are sometimes nipped off by flatfish but can regrow.

The boring sponge uses chemicals to dissolve tunnels in calcareous shells and rocks, creating a living space for itself.

FIXED TO THE BOTTOM

Christmas-tree worms live attached to the bottom in hard tubes that they cement into coral reefs. They feed by filtering plankton from the water, using their beautiful double spiral of tentacles.

Symbiosis Bottom-living is a challenge for marine organisms. A safe crevice on a coral reef, for instance, is valuable, but fiercely fought over. The solution to finding a home is often to enter an intimate relationship with a different organism—a situation called symbiosis. When only one partner benefits, the relationship is called commensal, and often involves one animal providing a home for the other. MUTUAL RELATIONSHIP Small pea crabs live inside mussels, The Banded Coral Shrimp earns its place gaining shelter and food, while the in the moray eel’s well-defended crevice by cleaning the teeth of its host. mussel merely tolerates their presence. Symbiosis in which both partners benefit is called mutualism. Many tropical gobies live in such relationships with blind or nearly-blind shrimp. The shrimp digs and maintains a sandy burrow that accommodates both, while its sharp-eyed partner goby acts as a lookout. Some anemones adhere to the shells of hermit crabs, gaining from the crab’s mobility and access to its food scraps. The crab is protected, in return, by the anemone’s stinging tentacles. The third type of symbiosis is parasitism, in which one partner, the host, is harmed. The crustacean Sacculina spreads funguslike strands through its host crab’s body to extract nutrients, weakening or killing the crab.

Large reef anemones often provide a haven for clownfish and tiny cleaner shrimp. The anemone benefits from the housekeeping activities of its guests.

OCEAN LIFE

A HOME IN EXCHANGE FOR CLEANING

218

INTRODUCTION TO OCEAN LIFE

Zones of Ocean Life

HUMAN IMPACT

NO PART OF THE OCEAN IS DEVOID

The northern and southern geographical limits of many shallow-water marine species are dictated by water temperature. Most species breed and disperse only within certain temperature limits. Climate change is slowly raising water temperatures and in the Northern Hemisphere, records have shown that some warmwater species are extending their ranges farther north. Similarly, some cold-water species may be expected to retreat farther north.

of organisms, from polar seas to the tropics and from coasts and the seashore to the deepest depths. The seabed and the water column above it both support a huge variety of life. However, marine organisms are distributed unevenly both horizontally and vertically. As on land, climate (mainly temperature) and food play a large part in determining distributions and biodiversity. In the harsh environment at the poles, there is less coastal life than in the warm tropics, but beneath the surface, Antarctic seas support rich marine communities. Although there is life at every depth, most creatures can only survive within particular depth zones at particular pressures, temperatures, and light regimens.

Geographical Zones Seawater temperatures are much more stable than those on land because water loses and gains heat more slowly than does air. However, the distribution of marine coastal and continental shelf communities still follows a global pattern, with distinct polar, temperate, and tropical ecosystems. Coastal salt marsh in temperate parts is replaced in the tropics by mangroves. Kelp forests only grow in cool waters but extend into the tropics in places where cold water upwells from the deep, such as off the coast of Oman on the Arabian peninsula. Planktonic species and bottom-living species with planktonic larvae might be expected to occur anywhere that ocean currents take them. However, a boundary between water masses with different physical characteristics may present as effective a barrier in an ocean as mountains do on land. Below a certain depth, there are fewer such barriers, and conditions are stable and similar worldwide, so deep-sea animals often have very wide distributions. KEY

CLIMATIC ZONES

The shape and tilt of our planet results in differences in the amount of solar radiation reaching land and ocean at different latitudes. This produces large-scale climatic zones that ring Earth.

equatorial

temperate

tropical

subpolar

subtropical

polar

OCEAN LIFE

Endemic Species Some marine organisms, especially pelagic species, have a wide MALDIVES ANEMONEFISH global distribution, since there are few barriers to their dispersal. This endemic fish is not a Others live in restricted geographical ranges and are said to be strong swimmer. It does not planktonic larvae and endemic to a particular sea, island, or country. The most remote have lives only in the Maldives patches of habitat, such as small oceanic islands, tend to have and Sri Lanka in the Indian the most endemic species. This is Ocean. Its host anemone has a wider distribution, because animals in their dispersive because its larvae disperse stages, such as eggs and larvae, may on ocean currents. survive only for short periods and so never reach distant shores. The Red Sea holds many endemic fish species. It is connected to the Indian Ocean only by a narrow channel and so is effectively isolated. Endemic fish are often those that cannot or do not swim GALAPAGOS PENGUIN far. Anemonefish, for example, lay This penguin species lives only their eggs on rocks under their around the Galápagos islands. The cold, upwelling Cromwell anemones and the young search for Current keeps them cool in spite new anemones on the same reef. of the tropical climate. They Flightless marine birds such as are isolated by the surrounding warm waters, so cannot disperse penguins are likewise restricted in beyond their home islands. their ability to colonize new areas.

SHIFTING ZONES

TROPICAL INVADER

Warm-water triggerfish stray as far north as southern Britain and have now begun to breed there. With continued ocean warming, they may become a native species.

ZONES OF OCEAN LIFE

219

Depth Zones As depth increases, so does pressure, while light, temperature, and food supply decrease. These changes impose limits on the types of marine organisms that can survive and prosper at different depths. The areas on and over continental shelves around the world are rich in life as they are well-supplied with nutrients from river discharge and stirred-up sediments. Shoaling fish, such as herring, feed on plankton sustained by the nutrients. Most commercial fisheries are over continental shelves. Below the continental shelf, no phytoplankton or seaweeds grow. Pelagic animals either eat each other or make daily feeding migrations into the upper layers. Rocky areas support a diverse fauna including coldwater coral reefs, sponge reefs, and hydrothermal vent communities. Fine sediments cover the immense, flat abyssal plains at 0 ft the foot of the continental slope. seaweeds While microorganisms abound, 160 ft sponge (50 m) large animals are relatively scarce. starfish

330 ft (100 m)

phytoplankton

zooplankton

500 ft (150 m) 650 ft (200 m)

SEABED IN THE SUNLIT ZONE

whale shark

Portuguese man-of-war

660 ft (200 m) SUNLIT ZONE On seabed, high biodiversity— seaweeds, corals, sessile animals; in water, rich plankton, abundant fish, cetaceans

mackerel salp

shark

TWILIGHT ZONE On seabed, crinoids, sponges, sea fans, sea pens, 6,500 ft sea cucumbers, Greenland (2,000 m) shark; in water, zooplankton, squid, shrimp, predators— sperm whale, silvery fish with large eyes, such as hatchet fish and lanternfish DARK ZONE On seabed, similar to twilight zone; in water, mostly small, darkcolored fish with large mouths and stomachs, gulper eels, rattails, anglerfish, red shrimp, deep-sea jellies

Seal breathing holes in sea ice create oases on the seabed beneath, where benthic organisms enjoy the benefits of a greater supply of light and nutrients.

squid

hatchetfish

Environmental conditions change gradually as depth increases, but zones can be recognized based on both physical and biological parameters. The types of marine life in each zone are shown here.

comb jelly

crinoid sponge

deep-sea anglerfish

9,800 ft (3,000 m)

VERTICAL LIFE ZONES

OASIS BENEATH THE ICE

tuna jellyfish

3,300 ft (1,000 m)

black swallower

hagfish ABYSSAL ZONE On seabed, few large animals, rattails, hagfish, and sea cucumbers, very diverse protists, nematode worms, bacteria; in water, some deep-sea fish

13,100 ft (4,000 m)

16,400 ft (5,000 m) HADAL ZONE Little-known region, but some large organisms found in deepest depths; deepest fish caught at 26,200 ft (8,000 m) 19,700 ft (6,000 m)

Ocean Deserts

OCEAN LIFE

cusk eel Some areas of ocean are similar to deserts on land and support few species. Clear, blue surface water over the deep oceans often supports only small amounts of plankton, because it is very poor in the nutrients and minerals needed by phytoplankton to grow. This is especially the case in areas where there are few storms to stir the water and bring nutrients up from deep water. The nutrient iron can be a limiting factor, and experiments in which areas were seeded with iron have shown greatly increased phytoplankton production. The ocean floor in abyssal depths can support only a few large animals BARREN POLAR SHORE and was once considered to be a virtual desert. This polar shore in Greenland However, recent work on deep-sea sediments has supports little life due to the grinding action of winter ice, though shown the opposite. If all the bacteria and tiny animals living between the sediment particles are counted, below the reach of the ice, rich communities may develop. then this habitat is as diverse as a tropical rainforest.

220

INTRODUCTION TO OCEAN LIFE

Ocean Migrations

DISCOVERY

FEEDING AND BREEDING ARE THE MAIN REASONS

Until recently, any journey made by a marine animal, such as the leatherback turtle shown below, was poorly understood because tracking devices used on land were inappropriate for use in water. This changed when satellitetracking devices became available. Attaching one to a turtle does not impede or harm it in any way but it can still pose problems.Yet turtles are threatened in the wild, so knowing where a female goes after laying her eggs is vital to conservation work.

TRACKING

that animals migrate. They move from one place to another, often at the same time of day or year, and usually follow the same, well-defined routes. Migratory species include many of the larger marine animals, such as whales and turtles, but smaller creatures, such as squid and plankton, also make spectacular journeys in order to survive and reproduce. Animal migration in the oceans is more complicated than on land because animals can move both horizontally and vertically through the water column.

Types of Migration The driving force behind any animal migration is survival. Individuals must eat to live, and some will travel long distances to find food. Such journeys often coincide with peak production times of plankton and other food sources in particular places, such as sites of seasonal upwellings. A shorter, more regular feeding migration is made daily by plankton and active swimmers such as squid (see p.221). A species’ survival depends on reproductive success. Gathering together and breeding in a few places at the same time optimizes conditions for offspring survival. Breeding grounds where food is abundant and conditions favorable are used repeatedly, with individuals often returning to their birthplace to breed. Some shore animals also migrate up and down the beach, following the outgoing tide to feed and avoiding immersion by returning before the tide turns.

T

NURSERY AREA

SPAWNING SITE

migration as plankton

MARINE MIGRATORY CYCLE

Some marine organisms migrate to a specific spawning site to release their eggs. The eggs hatch into larvae that join the plankton and drift in the currents to another nursery area, where they feed and mature before joining the adult population.

I OCEAN

OCEAN

A tracking device is being attached to this leatherback turtle on Juno Beach, Florida. In case an opportunity does not arise to remove it manually, parts of the harness are designed to gradually disintegrate.

spawning migration

OCEAN

C

PACIFIC

TRACKING TURTLES

migration of young adults

PACIFIC

N

migration route

ARCTIC TERN MIGRATION

return of adults after spawning

AT L A

MIGRATING TERN

ADULT POPULATION

INDIAN OCEAN

This small bird flies from the Antarctic to the Arctic to breed and then returns south, a round trip of nearly 22,000 miles (35,500 km). Terns spend 90 days at the nesting grounds each year. The rest of the time is spent mostly on the wing. summer distribution

winter distribution

LOBSTER MIGRATION

Caribbean spiny lobsters migrate in single file across the sea floor in winter, seeking warmer water, and return to shallow water in summer.

Migrating between Salt and Fresh Water Although some marine species can cope with a great range of salinity and temperature, only a few move between fresh and salt water at particular stages of their lives. Some, such as salmon, start and finish their lives in fresh water and spend the rest of their time in the ocean. Such fish are described as anadromous. Eels, on the other hand, start and finish their lives in the sea, but spend 10 to 14 years in fresh water while maturing. Fish such as these are termed catadromous. At maturity, both of these fish return to their birthplace to breed, after which they die. Changing from fresh to salt water or vice versa would be fatal to most fish, but various physiological adaptations, including the way their kidneys function, allow both anadromous and catadromous fish to make the transition without experiencing any ill effects.

OCEAN LIFE

SALMON RETURNS TO FRESHWATER SPAWNING GROUNDS

At three to five years of age, a coho salmon is ready to return to the river where it was born to spawn. Some mature at only two years, returning to their home river as “jacks.”

1

In migrating upstream to its spawning grounds, the salmon may swim 2,175 miles (3,500 km) against the water current, negotiating several waterfalls and rapids.

2

As soon as the female has deposited her eggs in the gravel on the riverbed, the male swims over them and releases his sperm, optimizing the chance of fertilization.

3

Newly hatched salmon live among the gravel until they absorb their yolk sacs and become fry. They then begin their journey downstream to the sea.

4

221

HORIZONTAL AND VERTICAL TRAVEL

Some animals migrate horizontally and vertically. Here, longfin squid migrate to spawn in May. They also move up and down the water column each day to feed.

Navigation While satellite tracking provides information on migration routes and confirms that many individuals travel the same path, how animals navigate over vast distances is still poorly understood. Salmon return to their spawning grounds by smelling the unique chemical composition of the water, but they first have to get close enough to pick up this scent. Some aquatic species may use water currents to guide them, while others use the Earth’s magnetic field to navigate. Animal migration is amazingly accurate, in terms of both direction and timing. Oceanic birds, turtles, and mammals can also navigate using the sun, the stars, and familiar landmarks.

DAY

Vertical Migrations

NIGHT

phytoplankton

phytoplankton

mackerel

jellyfish lanternfish copepods

mackerel

shark squid

660 ft (200 m)

BELUGA WHALES MIGRATING

copepods

Belugas, like these in Lancaster Sound, Canada, live in the Arctic and subarctic, but some migrate to warmer waters in summer.

squid

In temperate and tropical regions, zooplankton migrates to the ocean surface at night and then moves down again during the hours of daylight. In a single day, this vertical movement may range from 1,310 to 3,300 ft (400 to 1,000 m), depending on the size and type of animal involved. In polar regions, where darkness lasts for several months, zooplankton migrates up and down on a seasonal basis, being at the surface during summer and at depth in winter. It is thought that zooplankton rises to feed on the phytoplankton that lives in the surface waters, but then retreats to depth for safety, or possibly because it expends less energy in cooler water. Maturing planktonic larvae of animals such as crabs will eventually migrate to the sea floor and become benthic.

jellyfish

EARTH’S GREATEST MASS MIGRATION

lanternfish squid

3,300 ft (1,000 m)

OCEAN LIFE

shark

During the day, when many animals remain in the depths, out of sight of predators, the phytoplankton utilizes the Sun’s energy to produce food. At night, the biomass of the surface waters (the sunlit zone) increases by as much as 30 percent, as zooplankton comes up to feed on phytoplankton and is, in turn, eaten by various fish and other animals. This regular movement of animals up and down the water column is the greatest mass migration on Earth.

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INTRODUCTION TO OCEAN LIFE

Living Down Deep

THE DEEP-SEA ENVIRONMENT APPEARS INHOSPITABLE—cold, dark, and

with little food. However, it is remarkably stable: temperatures remain between 35 and 39ºF (2 and 4ºC) year-round, salinity is constant, and the perpetual darkness is overcome by novel communication methods (see pp.224–225). Although deep-sea pressures are immense, most marine animals are unaffected, since they have no air spaces, while animals living below about 5,000 ft (1,500 m) show subtle adaptations. Species diversity of large animals decreases with depth, but there is a huge diversity of small organisms living within deep-sea sediments.

OCEAN LIFE

Pressure Problems

DEEP-SEA ADAPTATIONS

Anglerfish have a lightweight skeleton and muscles for neutral buoyancy. This specimen’s muscles have been “cleared” to show the bone, which is stained red.

Deep-ocean animals experience huge pressures, but problems arise only in gas-filled organs such as the lungs of diving mammals and the swim bladders of fish. Sperm whales, Weddell seals, and elephant seals all dive to depths where their lungs are compressed, but their flexible rib cages allow this. While underwater, they use oxygen stored in blood and muscles. Deep-sea fish can cover a large vertical range because pressure changes at depth are proportionately less, per foot, than near the surface, so the pressure or size of their swim bladders does not change radically. In oceanic trenches, the pressure is so great that it affects the operation of biological molecules, such as proteins. Pressure-loving bacteria in this habitat have specialized SPERM WHALE proteins—they cannot Sperm whales can dive to at least 3,300 ft (1,000 m), where grow or reproduce when brought to the pressure is 100 times greater than at the surface. the surface.

LIVING DOWN DEEP

Finding Food

mouth surrounded by modified tube feet

The major problem of deep-sea living is finding enough food. With the exception of communities based around hydrothermal vents and cold seeps (see pp.188–89), animals living in the deep ocean and on the deep-ocean floor are ultimately reliant on food production in the sunlit layer, thousands of feet above. In the depths, it is too dark for plant plankton to live and to provide food. Sometimes, large mammal or fish carcasses reach the sea bed, but most food arrives as tiny food fragments, slowly sinking from above. Much is eaten before it reaches the sea floor, but much is also added in the form of skins, shed from mid-water crustaceans and salps. Bacteria grow on such material, helping it to clump together and so fall more rapidly.

SEABED CONSUMER

The fangtooth lives at midwater depths of about 1,600–6,500 ft (500–2,000 m). Food is scarce, so its large mouth and sharp teeth help it to catch all available prey.

DISCOVERY

OBSERVING DEEP-SEA LIFE Before the advent of modern research submersibles, few biologists had the opportunity to see deep-sea animals alive and in the wild. Dredged and netted specimens are often damaged, and little can be learned from them about the animal’s way of life. Modern submersibles have an excellent field of view, are equipped with sophisticated cameras and collecting equipment, and can operate to depths of 3,300 ft (1,000 m) or even 20,000 ft (6,000 m).

tube foot, used to move across seafloor

MIDWATER FEEDER

223

Sea cucumbers vacuum up organic remains from the sea floor. At high latitudes, more food rains down in spring, following surface phytoplankton blooms; these rains may trigger sea cucumbers to reproduce.

Scavenging Giants Many deep-sea animals are smaller than their relatives in shallow water. This is an evolutionary response to the difficulties of finding food in the deep ocean. However, some scavengers survive by growing much larger than their shallow-water counterparts. For example, amphipod and isopod crustaceans that measure only about ½ in (1 cm) long are common in shallow water, where they scavenge on rotting seaweed and other debris. Carrion in the deep sea is sparse, but it comes in big, tough lumps such as whale carcasses. Some deep-sea amphipods grow to a length of 4–6 in (10–15 cm), more than ten times larger than shallow-water species, and so are able to tackle such a bonanza. In the low temperature of the deep ocean, these animals move and grow slowly and reproduce infrequently, but live much longer than their shallow-water counterparts. Sea urchins, hydroids, seapens, and other animals also have giant deep-sea forms. Similar giants are found in cold Antarctic waters.

A WINDOW ON DEEP-SEA LIFE

Deep Rover is a two-person submersible capable of diving to 3,300 ft (1,000 m), launched from a semi-submersible platform. The occupants can see all the way around through the acrylic hull.

Staying Aloft Huge areas of the deep-sea floor are covered in soft sediments many yards thick, called oozes (see p.181). Seabed animals need ways of staying above these sediments so that they can feed and breathe effectively. Many sedentary filter-feeding animals, such as sea lilies, sea pens, and some sponges, have long stalks, enabling them to keep their feeding structures above the sediment. Some sea cucumbers have developed stiltlike tube feet that help them walk over the sediment surface, instead of having to plow through it. Similarly, the tripodfish props itself up on its fin tips. One species of sea cucumber, Paelopatides grisea, has an unusually flattened shape that allows it to lift itself off the sea bed with slow undulations of its body. SEA LILIES ANCHORED IN THE OOZE

To catch food, sea lilies reach up into the current on stalks up to 2ft (60cm) high. The stalk extends deep into the sediment to provide an anchor.

DEEP-SEA GIANT

The widespread deep-sea scavenger amphipod Eurythenes grows to over 3 in (8 cm).

OCEAN LIFE

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INTRODUCTION TO OCEAN LIFE

Bioluminescence BIOLUMINESCENCE IS A COLD LIGHT

produced by living organisms. On land, only a few nocturnal animals, such as fireflies, produce light, but in the ocean, thousands of species do so. Deep-water fish and squid use bioluminescence extensively, but there are many other light producers, such as species of bacteria, dinoflagellates, sea pens, jellyfish, mollusks, crustaceans, and echinoderms. Evidence suggests that marine organisms use bioluminescence for defense (as camouflage or distraction), for finding and luring prey, and for recognizing and signaling to potential mates.

Light Production

pigment cup

Many bioluminescent marine organisms use their light in communication. This bristlemouth fish can signal to its own kind with its specific photophore pattern.

light source lens

rays Bioluminescence is produced by a chemical into reaction in special cells known as photocytes, focused beam and carried away usually contained within light organs called from source photophores. A light-producing compound called luciferin is oxidized with the help of an LENS enzyme called luciferase, releasing energy in the form of a cold light. Most bioluminescent light is pigment light cup source blue-green, but some animals can produce green, yellow, or, more rarely, red light. A range of light-producing structures is found in different animals. The hydroid Obelia has single photocytes scattered in its tissues, while certain fish and squid have complex photophores with lenses and light filters. Some animals, including flashlight and eyelight pipe LIGHT PIPE fish, some anglerfish, ponyfish, and some squid, adopt a different strategy. pigment TYPES light They culture symbiotic, PHOTOPHORE cup source Photophores often feature a bioluminescent bacteria pigment cup and a lens that directs in special organs. The the light into a parallel beam. With a light pipe, light can be bacteria produce their filter allows light and are, in return, channeled from the photophore, deep-red which might be buried in the only pigment fed nutrients by their animal’s body. Color filters in deep-red filter light host and given a safe front of the light source fine-tune COLOR FILTER to pass place in which to live. the color of the emitted light.

HUNTING WITH A SPOTLIGHT

The dragonfish produces a beam of red light, from a photophore beneath its eye, to spotlight its prey. Red light is invisible to most deep-sea animals.

Light Disguise

body covered with tiny, flashing photophores

Animals using bioluminescence to attract prey, or to signal to each other, risk alerting their own predators to their presence. However, lights can also be used for camouflage. Hatchetfish live at depths where some surface light is still dimly visible. To keep their silhouette from being seen from below, they manipulate the light they emit from photophores along their belly, to mimic the intensity and direction of the light coming from above. Bioluminescence is also used to MANIPULATING LIGHT confuse potential predators. Flashlight fish The silvery, vertical flanks of turn their cheek lights on and off. Some hatchetfish reflect downwelling squid, shrimp, and worms eject luminous light, and their photophores shine secretions or break off luminous body parts downward, camouflaging their silhouette from below. that act as decoys, while they escape.

OCEAN LIFE

USING LIGHT TO COMMUNICATE

LUMINOUS SMOKESCREEN

organs producing downward-directed beams of light

A firefly squid presents a predator with a myriad of confusing pinprick lights emitted from its body. It can also secrete a cloud of luminous particles into the water to act as a smokescreen, allowing it to escape.

squid’s ink is bioluminescent

BIOLUMINESCENCE

bioluminescent organ produces light and directs it downward; the light merges with light downwelling from the sky and conceals the animal from predators below

225

light organs form a distinctive pattern recognized by other bristlemouths

Predators In the unlit regions of the deep ocean, many hunters try to attract prey, rather than go in search of it. After all, hunting light-producing bacteria cause by sight and chasing prey is difficult lure to glow where the only available light is from bioluminescence. An obvious way of attracting prey is to use a luminous lure, and anglerfish are especially good at this. Anglerfish in the genus Linophryne have a head lure, like a fishing rod, lit by luminous bacteria, and a chin barbel with tiny photophores that produce their own light. Midwater fish often have thin skeletons and weak muscles to improve their buoyancy, so luring prey is an energy-efficient way for them to hunt. Stauroteuthis syrtensis, an `unusual deep-sea octopus with glowing suckers, sets a deadly trap. Its eight tentacles are connected into a web, and GLOWING JELLYFISH its modified suckers, which have lost the ability to LUMINOUS LURE The mauve stinger glows grasp, are bioluminescent. Although this species has Fish are attracted to the luminous lure of with bioluminescence when never been seen hunting, its prey (which are primarily deep-sea anglerfish and are quickly snapped it is disturbed by waves, and copepods) is probably lured toward the raised, up. Most anglerfish are brown or black so can also produce a luminous that they do not light themselves up. mucus if it is touched. light-emitting arms, and then enfolded and eaten.

Phosphorescence

Dinoflagellates are tiny, single-celled organisms that emit bright flashes of light when disturbed. In large numbers, they produce “phosphorescent” seas.

OCEAN LIFE

On a still, warm night, especially in the tropics, moving boats leave a glittering trail of light in their wake and divers can create swirling pinpricks of light by simply moving around. This phenomenon is caused by bioluminescent plankton, mostly dinoflagellates. Their light is often informally called phophorescence, because it is emitted when they are disturbed, but decays after a few seconds. Biological phosphorescence is thought to be an anti-predation device. When dinoflagellates are attacked by planktonic copepods, they flash. This alerts nearby shrimp and fish to the copepods’ presence, and the copepods themselves may then become prey. Some dinoflagellates, such as Gonyaulax polyedra, only produce light at night, so they do not waste energy on light production when it cannot be seen. Deep-sea jellyfish may use a similar antipredator strategy. The jellyfish light up only when disturbed by vibrations, which indicate an approaching predator. Often, a series of erratic flashes travels over the entire body surface. Such lights may serve to distract the predator.

BIOLUMINESCENT PLANKTON

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INTRODUCTION TO OCEAN LIFE

The History of Ocean Life LIFE HAS BEEN PRESENT IN THE OCEANS

for over 3,500 million years. The great diversity of today’s marine life represents only a minute proportion of all species that have ever lived. Evidence of early life is hard to find, but it is seen in a few ancient sedimentary rocks. The fossil record has many gaps, but it is the only record of what past life looked like. Fortunately, many marine organisms have shells, carapaces, or other hard body parts, such as bones and teeth. They are more likely to be preserved than entirely soft-bodied creatures, although in exceptional circumstances these have also been fossilized. Using fossils, and information from the sediments in which they are preserved, scientists can reconstruct the history of marine life.

3,800–2,200 Million Years Ago The Origin of Life

EARLY MICROFOSSILS

This micrograph of a section of chert (a form of silica) from the Gunflint Formation, Canada, includes 2,000 million-year-old microfossil remains. These micro-fossils contain the oldest and best-preserved fossil cells known.

When arth formed, it was totally unsuitable for life. The atmosphere changed, however, and the oceans formed and cooled (see pp.42–43), so that by 3,800 million years ago, conditions allowed biochemical reactions to take place. It is thought that simple, water-soluble organic compounds called amino acids accumulated in the water, eventually forming chains and creating proteins. These combined with other organic compounds, including selfreplicating DNA, to form the first living cells. Earth’s atmosphere was further developed by mats of algae and cyanobacteria called stromatolites, whose fossil record stretches from over 3,500 million years ago to the present day. Stromatolites could perform photosynthesis, and their growth eventually flooded the atmosphere with oxygen. Cyanobacteria are single-celled organisms with DNA but no nucleus or complex cell organelles. It was not until 2,200 million years ago that cells with nuclei and complex organelles (eukaryote cells) appeared.

620–542 MYA Precambrian Life Ancient life, though soft-bodied, fossilizes under certain conditions, offering rare glimpses of early multicellular life. About 620 million years ago, a community of soft-bodied animals known as the Ediacaran fauna left their body impressions and trackways in a shallow sea bed. The sea bed now forms the sandstone of the Ediacaran Hills in Australia, where the fauna was discovered in the 1940s. The ancient sea was inhabited by strange, multicellular animals. Some resembled worms and jellyfish, but others were thin, flat, and unfamiliar, making it difficult to know if they are related to existing animals or a separate, extinct, evolutionary line. These animals are the only link between the single-celled organisms that preceded them and the rapid diversification of life that followed. Ediacaran fauna are also found in Namibia, Sweden, Eastern Europe, Canada, and the UK. EDIACARAN FOSSILS

OCEAN LIFE

These are typical examples of Ediacaran fossils preserved as impressions in rock. Mawsonite (left) is believed to be a complex animal burrow; Spriggina (below) may be an arthropod, or a new life-form.

PEOPLE

A.I. OPARIN In 1924, Russian biochemist Aleksandr Oparin (1894-1980) theorized that life originated in the oceans. He suggested that simple substances in ancient seas harnessed sunlight to generate organic compounds found in cells. These compounds eventually evolved into a living cell.

THE HISTORY OF OCEAN LIFE

227

550–530 MYA Cambrian Explosion

FIRST REEFS

The Cambrian reefs were built by extinct sponges called archaeocyathids. They resembled tube sponges (above), having a similar shape and a calcareous skeleton.

Over the course of 20 million years, around the start of the Cambrian Period, many life-forms made a sudden appearance. Indeed, most of today’s major animal groups (phyla) abruptly appear in the fossil record. The Cambrian Explosion of evolution may have been caused by the creation of new ecological niches as the coastline increased, due to the breakup of the Rodinia supercontinent. Further niches arose as a rise in sea level produced large expanses of warm, shallow water. The Cambrian seas were dominated by arthropods, chiefly trilobites, but there were also foraminiferans, sponges, corals, bivalves, and brachiopods. All readily fossilize, as they each have some sort of mineralized “skeleton.” ARTHROPOD TRAILBLAZERS

Trilobites evolved a multitude of different body forms and remained a ubiquitous arthropod group for the next 100 million years. They became extinct during the Permian Period.

BRACHIOPODS

Brachiopods may resemble bivalve molluscs, but they are unrelated life-forms and were among the first animals to appear in the Cambrian Period. Over 3,000 genera have been described. Only about 400 species survive today.

418–354 MYA The Age of Fish LIVING MARINE STROMATOLITES

Built by Earth’s oldest type of organism, stromatolites are now found in only a few places such as here, in the hyper-saline water of Hamelin Pool, Australia.

The earliest vertebrate fossils known are jawless fish that lived some 468 million years ago. Jawed fish appeared in the Silurian Period, following the development of massive coral and sponge reefs that provided them with a multitude of habitats in which to diversify. The now-extinct acanthodians, with their prominent spines on the leading edges of their fins, were among the earliest of these. Having hinged jaws allowed fish to feed more efficiently, and paired fins gave them the speed and manoeuvrability to hunt. The following Devonian Period (418–354 million years ago) saw an evolutionary radiation that could be called the “Age of Fish.” Armored fish called placoderms dominated Devonian seas, some reaching lengths of 20 ft (6 m). Ray-finned fish, sharks, and lobe-finned fish also appeared at this time and have survived to the present day, although marine lobe-finned fish are known only from the Coelacanth. Lobe-finned fish are important in the fossil record because one group gave rise to early tetrapods (limbed vertebrates).

EVOLUTIONARY INSIGHT EARLY JAWLESS FISH

Jawless fish first evolved in the ocean, later spreading into brackish and freshwater habitats. The bony head shield and dorsally situated eyes of this Cephalaspis suggest it is a bottom-dweller.

This lobe-finned fish, Tiktaalik roseae, has gills and scales like a fish, but has tetrapodlike limbs and joints. This “missing link” helps to reveal how animals moved from the oceans onto land.

Mimia, a small, ray-finned fish

Cladoselachii, one of the few sharks in the seas at this time

The Devonian reef fauna (right) from Gogo, Australia, is typical of the time. It is dominated by a wide variety of armored placoderms, but ray- and lobe-finned fish, and a shark, have also been found there.

Rolfosteus, a long-snouted placoderm with crushing toothplates

Bothriolepis, a bottom-dwelling placoderm

phyllocarid, a relatively common shrimp-like crustacean

Nautiloid, a primitive marine shelled cephalopod

rugose coral; common in Devonian seas, now extinct tabulate coral, now extinct

OCEAN LIFE

DEVONIAN COMMUNITY

Eastmanosteus, a large placoderm and active predator

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INTRODUCTION TO OCEAN LIFE

252–65 MYA Giant Marine Reptiles

PEOPLE

MARY ANNING

During Triassic, Jurassic, and Cretaceous times, evolution of reptiles, similar to that of the dinosaurs on land, occurred in the oceans. Between 252 and 227 million years ago, three groups appeared—turtlelike placodonts, lizardlike nothosaurs, and dolphinlike ichthyosaurs. Of these, only ichthyosaurs survived until the Jurassic. The Jurassic oceans teemed with life. Modern fish groups were well represented, as were ammonites, mollusks, squid, and modern corals. A variety of ichthyosaurs evolved, some giant forms reaching 30 ft (9 m) in length, but they soon died out and were replaced by modern sharks. The gap left by the extinction of the placodonts and nothosaurs was filled by long-necked plesiosaurs. Those with a short body and tail and a small head lived in shallow water, while larger forms, called pliosaurs, probably lived in deep water. It is also likely that some of the flying reptiles, called pterosaurs, lived on coastal cliffs and survived by eating fish caught at the water’s surface. During the Cretaceous Period, reptiles remained the largest marine carnivores, (plesiosaurs now coexisting with mosasaurs, distant relatives of monitor lizards,) but none survived the mass extinction that occurred 65 million years ago.

Lyme Regis in Dorset, UK, is famous for its Jurassic fossils, and is where Mary Anning (1799-1847) found and collected her nowfamous ichthyosaur and plesiosaur skeletons. She was one of the first professional fossil collectors. FOSSILIZED ICHTHYOSAUR

The dolphinlike features of this ichthyosaur are evident from its fossilized remains. The powerful tail was half-moon-shaped, but here only the down-turned backbone is preserved.

dorsal vertebrae with attachment points for long ribs rib

long neck comprising 30 vertebrae

PLESIOSAUR

Cryptoclidus eurymerus is a mid-Jurassic plesiosaur. It has a small head, long neck, and short tail, which is typical of shallowwater forms. Its sharp teeth indicate that it ate small fish or shrimplike crustaceans. bones of shoulder girdle are flattened into thin plates

pointed, interlocking teeth trap prey

paddlelike hind flipper large bones of pelvic girdle

TIMELINE OF EARTH HISTORY 4,000 MYA

Million 4,100 MYA years ago CRYPTOZOIC EON 4,500–542 MYA

first organic molecules

3,500 MYA

3,000 MYA

first stromatolites

50–14 MYA Return to Water

OCEAN LIFE

ANCIENT WHALE SKELETON

This skeleton has been exposed in a desert in Saccao, Peru. Whales evolved over the last 50 million years, so this area must have been an ancient sea at some point in this period. SKULL WITH A BLOWHOLE

The nostrils of Prosqualodon davidi are positioned on top of the head, forming a blowhole. This feature proves that this fossil skull is from a primitive whale.

Following the mass extinction that saw the demise of marine reptiles, some mammals that had evolved on land began returning to the water. Around 50 million years ago, the oceans started to resemble modern oceans in terms of their geographical positions and fauna. The ancestors of whales, however, were unlike their modern counterparts. The earliest whale, Pakicetus, was probably a close relative of the hoofed mammals (ungulates), but it is known only from its skull. Ambulocetus, which means “walking whale,” is another early form. It had few adaptations for living in water and probably still spent much time on land. The productivity of the oceans increased, whales diversified, and other marine mammals appeared. Whales similar to today’s toothed whales appeared first, and a few million years later, baleen whales evolved. By 24 million years ago, baleen whales had reached today’s giant sizes, suggesting that plankton was present in vast numbers for them to feed on. Only 14 million years ago, pinnipeds and sirenians (dugongs and manatees) evolved. It is thought that pinnipeds arose from a family of carnivores not unlike otters. Their present-day forms are seals, sea lions, and walruses.

2,500 MYA first microfossils

2,200 MYA

first eukaryotes and multicellular algae

HUMAN IMPACT

LIFE ON THE MOVE Humans have long had a profound effect on the oceans through pollution, overfishing, and linking oceans with canals. People have also transported marine organisms all over the world, in and on their ships, without knowing what long-term impact this will have.

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Today: Life in Modern Oceans

GRAY REEF SHARK

Like its close relative the Caribbean reef shark (below), this shark lives in warm, shallow waters, near coral atolls and in adjacent lagoons. It is found in the Indian and Pacific oceans, but it is cut off from the Atlantic.

CARIBBEAN REEF SHARK

PA L 65 AE –2 OG 3.3 E M NE YA NE O 23 GE .3– N QU 1.8 E 1.8 ATE MYA –P RN RE AR SE Y NT

CR 14 ETA 2– CE 65 O M US YA

JU 19 RAS 9.5 S –1 IC 42 M YA

Like the gray reef shark (above), this species lives in shallow water near coral reefs. Its range is isolated from the Indo-Pacific by the deep, cold ocean around South Africa, so it is restricted to warm parts of the Atlantic, from the Caribbean to Uruguay.

M I 35 SSI 4– SS 32 IP 3 M PI YA AN PE NN 32 S 3– Y 29 LV 0 M AN YA IAN PE R 29 MI 0– AN 25 2M YA TR I 25 ASS 2– IC 19 9.5 M YA

SI L 44 UR 3– IA 41 N 8M YA DE 41 VON 8– IA 35 N 4M YA

OR 49 DOV 0– IC 44 IA 3M N YA

CA 54 MB 2– RI 49 AN 0M YA

ED 63 IAC 5– AR 54 AN 2M YA

We know much more about life in today’s oceans because, as well having entire organisms to study, we can also observe life cycles, locomotion, and behavior. Each of the five oceans supports a wide variety of life. Some species are very specialized and are restricted to a small area, while others are migratory or generalists and have a wider distribution. Sometimes, closely related species live in the same habitat in different oceans, separated by land or other physical barriers (see right). By studying living organisms and the characteristics of the water they live in, scientists can also better understand ancient ocean environments and organisms. The deep ocean is still poorly known, but it contains an ecosystem that could be crucial to our understanding of life—black and white smokers (see p.188). Isolated from sunlight and from the surrounding water by a steep thermal gradient, it is possible that this is the type of environment in which life first evolved 3.5 billion years ago.

earliest sharks appear fourth mass extinction Cambrian Explosion: rapid evolution of body forms

635

600

550

first lobe-finned fish appear

first armored fish appear

450

500

400

earliest penguins

third mass extinction

350

300

first turtles appear

250

200

150

100

second mass extinction plactodonts (earliest marine reptiles) appear

earliest jawless fish, representing the first vertebrates, appear

1,500 MYA

2,000 MYA

plesiosaurs replace placodonts ichthyosaurs appear

1,000 MYA

700 MYA

mosasaurs replace ichthyosaurs

635 MYA PHANEROZOIC EON 542 MYA–PRESENT

first fossil evidence of mineralized skeletons

Mass Extinctions

This ammonite species is one of the few to survive the lateTriassic mass extinction event.

fifth mass extinction kills last ammonites

PRESENT DAY

beginning of the Ediacaran period, which soon features the first multicellular life

VOLCANIC ARMAGEDDON

Volcanic activity in the western Ghats of India is now thought to have been a factor in the most recent mass extinction. The eruptions would have caused destruction and climate change on a global scale.

OCEAN LIFE

The history of life is punctuated by five mass extinctions—catastrophic events in which many life forms died out. The first occurred 443 million years ago, when prominent marine invertebrates disappeared from the fossil record. About 368 million years ago, global cooling and an oxygen shortage in shallow seas caused about 21 percent of marine families to disappear, including corals, brachiopods, bivalves, fishes, and ancient sponges. At the end of the Permian Period, 252 million years ago, the cooling and shrinking of oceans killed over half of all marine life. Another mass-extinction event at the end of the Triassic Period, 199.5 million years ago, caused major losses of cephalopods, especially the ammonites. The fifth extinction, 65 million years ago, caused the demise of the dinosaurs; in the oceans, it caused the giant marine reptiles to disappear. The next mass extinction is likely to be a result of human activity. AMMONITE FOSSIL

50 whales diversify

first mass extinction

Ediacaran fossils show early multicellular life

whales evolve from terrestrial mammals

LIFE ON EARTH was once thought to fall into

five great kingdoms—the animals, plants, and fungi, and the two microscopic kingdoms, the protists and the bacteria. Scientists are now looking at life ever more closely, and each discovery expands our perspective on life’s vast variety. Many experts now consider that the familiar life-forms, plants and animals, represent just two of 30 or more kingdoms. The oceans are the ancestral home of life and are still home to all major groups of animals. Although plants are far more diverse on land, their place is taken in the oceans by a range of seaweeds and microorganisms. The following section showcases the entire range of ocean life. It is organized into kingdoms and further divided into the smaller units used by scientists to order and understand nature.

KI N GD OMS OF O C E A N L IF E SUCCESS IN WATER

This violet-spotted reef lobster is a flamboyant example of one of the marine success stories of the animal kingdom—the varied and abundant crustaceans. The crustaceans as a group include crabs, crayfish, shrimp, and some of the most common members of the zooplankton.

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BACTERIA AND ARCHAEA

Bacteria and Archaea THE SMALLEST ORGANISMS ON EARTH

are the bacteria and their relatives, the archaea. Bacteria occupy virtually Archaea all oceanic habitats, whereas many archaea are confined KINGDOMS 13 to extreme environments, such as deep-sea vents. Bacteria SPECIES Many millions and archaea play vital roles in the recycling of matter. Many are decomposers of dead organisms on the ocean floor. Others are remarkable in being able to obtain their energy from minerals in the complete absence of light.

OCEAN LIFE

DOMAINS Bacteria

Anatomy

Habitats

Bacteria and archaea are singlecelled organisms that are far smaller than any other, even protists. Most have a cell wall, which, in bacteria, is made from a substance called peptidoglycan. None has a nucleus or any of the other cell structures of more complex organisms (eukaryotes). Some bacteria and archaea can move by rotating threads called flagella; others have no means of propulsion. Scientists separated the Archaea and Bacteria groups on the basis THRIVING IN THE RIGHT CONDITIONS of chemical differences in their cell The bacterium Nitrosomonas forms colonies make-up. All living cells contain wherever there is enough ammonia and oxygen in the water. tiny granules (ribosomes), which help to make proteins, but those in archaea are differently shaped to those in bacteria. The oily substances that make up their cell membranes are also different. Additionally, archaea have special molecules associated with their DNA that protect them in the harsh environments in which they live. Scientists now think that their chemical HEAT-LOVING ARCHAEA differences are sufficiently important to rank Most archaea can adapt Archaea as a distinct evolutionary branch of to extreme conditions. This life. Initially considered to be primitive, the heat-loving example, GRI, archaea are now thought to be closer to the was ejected from the sea ancestors of eukaryotes than are the bacteria. floor in an undersea eruption.

Bacteria are found throughout the ocean environment, because nearly all habitats provide them with the materials necessary to obtain energy. Most bacteria get energy by breaking down organic matter. Much of this matter accumulates on the ocean floor and provides excellent conditions for the decomposer bacteria. Bacteria are also found in large numbers in the water column, feeding on suspended matter. A few kinds of bacteria, such as cyanobacteria, can photosynthesize and so live nearer to the surface, in brightly lit waters. Some form colonies and build huge structures, called stromatolites, near the shore. Many archaea and bacteria can live in extreme conditions, such as high temperatures, water with high acidity, or low oxygen levels. For example, archaea and bacteria live around deep-sea vents, getting their energy from chemical reactions of methane and sulphide compounds ejected by the vents. Others survive in the very high concentrations of salt on some sea shores.

HYPER-SALINE CONDITIONS

The hyper-saline water of Hamelin Pool, west Australia, is one of only three places where stromatolites are found. The rocks are formed by the cyanobacteria cementing sediment particles together.

PEOPLE

CARL WOESE Born in New York Carl Woese (1928—2012) was the microbiologist who is responsible for the current division of living organisms into three domains, Archaea, Bacteria, and Eucarya, on the basis of his research into the RNA (a chemical related to DNA, called ribonucleic acid) found in ribosomes. Woese put forward his new classification in 1976, but it was not until the 1980s that his hypothesis was accepted.

LIVING ON THE SEA BED

Bacterial mats form on the sea bed where oxygen supply is low. This mat of Beggiatoa sp. is at the mouth of the Mississippi, USA.

BACTERIA AND ARCHAEA DOMAIN BACTERIA

DOMAIN BACTERIA

Oscillatoria willei SIZE

DISTRIBUTION

DOMAIN BACTERIA

Trichodesmium erythraeum 1–10mm per colony

DISTRIBUTION

SIZE

Tropical waters

Once known as blue-green algae, cyanobacteria are bacteria that are able to use photosynthesis to make foods in a similar way to plants. Oscillatoria willei and other related cyanobacteria occur in rows of similarly sized cells that form filaments called trichomes. Many trichomes are enveloped in a firm casing, but in Oscillatoria the casing is thin or may be absent altogether, which allows the filaments to glide quickly forwards, backwards, or even to rotate. Some species of Oscillatoria can fix nitrogen but, unlike Trichodesmium (below), they may not have cells specialized for the purpose.

SIZE

Calothrix crustacea

Filament length 0.13mm

Tropical and subtropical seas

worldwide

Filament length 0.15mm

DISTRIBUTION

Fragments of filaments, called hormogonia, which consist of dozens of cells, sometimes break off and glide away to establish new colonies. These bacteria may cause skin irritations in humans who come into contact with them in tropical waters.

Worldwide

Forming single filaments or small bundles, bacteria of the genus Calothrix are widespread in oceans everywhere. Unlike those of Oscillatoria and Trichodesmium (left), the filaments of Calothrix crustacea have a broad base and a pointed tip that ends in a transparent hair. The filament has a firm or jelly-like coating, which is often made up of concentric layers that may be colourless or yellow-

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brown. Unusually, the filament grows in much the same way as a plant root, its growth being confined to a special region just behind the tip, called a meristem. Sometimes, the filament sheds the tapering tip above the growth region, enabling Calothrix to reproduce asexually by casting off fragments called hormogonia from the meristem. These fragments are able to form new filaments far away from the parent. These kinds of cyanobacteria often form slimy coatings on coastal rocks and seaweeds. At least one species of Calothrix is known to make up the photosynthetic part of some rocky shore lichens, such as Lichina pygmaea (p.255).

oceanic food chains. The bacteria form long colonial filaments, in which some cells carry out nitrogen fixation, while others are specialized for photosynthesis. These tasks must be separated because the oxygen by-product that results from photosynthesis would interfere with the nitrogen-fixing process, so they cannot both occur in the same cell.

Individual filamentous colonies of the cyanobacteria Trichodesmium erythaeum are just visible to the naked eye, and these bacteria have traditionally been known as sea sawdust by mariners. Under warm conditions, the bacteria is able to multiply extremely rapidly to create massive blooms that may have such an extent that they are visible from space. This is a prolific nitrogen-fixing bacterium that harnesses about half of the nitrogen passing through

DOMAIN BACTERIA

Vibrio fischeri SIZE

0.003mm cell length

DISTRIBUTION

Worldwide

Many marine organisms, particularly those in the deep sea, make use of bioluminescence, the biochemical emission of light. Many of these creatures depend on bacteria, such as the rod-shaped Vibrio fischeri, to generate the light, and in these cases

the bacteria live within the body of their host in a mutually beneficial relationship. The bacteria produce light using a chemical reaction that takes place inside their cells. Vibrio fischeri also occurs as a free-living organism, moving through water by means of a flagellum and feeding on dead organic matter. The distinctive, comma-shaped cells seen in Vibrio fischeri, below, are characteristic of the genus. Other Vibrio species (which are not luminescent) are responsible for the potentially fatal disease cholera.

EYE LIGHTS Eyelightfish (such as the one shown below) have light-emitting organs called photophores under each eye. The light is produced by colonies of Vibrio fischeri living in the photophores. The light organs can be covered and uncovered, and may be used as an aid to recognition and communication between fish of this species. The ability to emit light may also play a part in prey capture and the avoidance of predators.

DOMAIN ARCHAEA

Halobacterium salinarium SIZE

0.001–0.006mm

DISTRIBUTION

Dead Sea and other hypersaline areas

of the world

OCEAN LIFE

Archaea that have adapted to live in waters with exceptionally high salt concentrations are called halophiles. One example of this type of organism is Halobacterium salinarium, which is rod-shaped, produces pink pigments called carotenoids, and forms extensive areas of pink scum on salt flats. The cell membranes of halophiles contain substances that make them more stable than other types of cell membrane, preventing them from falling apart in the high salt concentrations in which they live. Their cell walls are also modified, for the same function. These archaea obtain nourishment from organic matter in the water. In addition, their pigments absorb some light energy, which the bacteria then use for fuelling processes within the cells.

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CHROMISTS

Chromists

GIANT CHROMISTS

The largest chromists are brown seaweeds called kelps. Firmly attached to rocks, they are seen flourishing in this clear, shallow water along the coast of South America.

MOST CHROMISTS

are microscopic in size, including many of the PHYLA At least 11 important photosynthetic SPECIES 31,200 plankton groups such as diatoms. However, brown seaweeds, which can grow to a huge size, are also chromists and unlike green seaweeds are not considered to be true plants. Like true plants, chromists make their own food by photosynthesis but they use different pigments to capture the sun’s energy. DOMAIN Eucarya

Anatomy Brown seaweeds and the various kinds of microscopic chromists all have very different shapes and structures. Their shared characteristics are at the cellular level. Chromists use an additional type of chlorophyll (a pigment) for photosynthesis and, unlike true plants, the food they manufacture is not stored as starch. They also have other colored pigments, which give brown seaweeds their color. Like green and red seaweeds, brown seaweeds do not need roots to absorb water and nutrients. Some have stiff stalks (stipes) and gas-filled bladders (pneumatophores) that hold up their leaflike fronds to the light. Some microscopic chromists, such as diatoms, have a rigid outer skeleton and float passively. Others, including dinoflagellates, can propel themselves along using whiplike threads called flagella.

BROWN SEAWEED

In place of roots, brown seaweeds have a holdfast which acts as an anchor. In this one, called Laminaria hyperborea, the holdfast is a small disk. DIFFERENT SHAPES

There are thousands of species of diatoms. Each has a differently shaped silica skeleton.

OCEAN LIFE

CHROMIST OR PROTIST?

DRIFTING PLANKTON

Radiolarians use their delicate arms to trap food particles and aid buoyancy as they float in the plankton.

Scientists used to place all single-celled eukaryotes including microalgae, protozoans, and chromists in one taxonomic group, the Protista. Today the term protist is used informally to indicate any of these diverse unicellular organisms. But there is no final agreement as to whether all the organisms included as chromists in this book really belong together in this kingdom.

CHROMISTS

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Habitats Chromists live in every ocean in the world. Others need sunlight to photosynthesize, so the microscopic forms, most of which are phytoplankton, are only found in the well-lit surface layers. Some, such as foraminiferans can live on the seabed, along with brown seaweeds, which often dominate rocky seashores in cooler climates. Great underwater forests of brown kelps grow in colder waters but they and most other brown seaweeds do not usually grow below about 66 ft (20 m). Some brown seaweeds grow unattached in sheltered lagoons and sea lochs, and a few grow in salt marshes anchored in mud.The brown sargassum or gulfweed, Sargassum natans, is unusual in that it floats at the surface of the open ocean, forming the basis for a unique ecosystem (see p.238). PLANKTON BLOOM

The milky bloom in this satellite image off Cornwall, UK, is of the coccolithophore Emiliania huxleyi, which has multiplied rapidly in favorable conditions.

Life Strategies Most single-celled chromists drift in the ocean surface layers as phytoplankton. They reproduce by splitting into two and some can do so very rapidly (see above). They can also reproduce sexually, forming the equivalent of egg and sperm cells. Their number increases dramatically with the warmth and longer days of spring and summer. Many seashore brown seaweeds produce slippery mucus, both to protect from drying out and to deter grazers. While some brown seaweeds are annuals, living for only a year, large species are usually perennial. NEW KELP GROWS FROM OLD

A new, yellow frond is growing from the top of this kelp stipe. The old frond, which will drop off, is covered in white animals called bryozoans, which block vital photosynthesis. upper valve of pillbox-shaped diatom

DIATOM DIVISION

When this diatom Coscinodiscus granii divides, the two halves will separate such that each daughter cell inherits one valve from its parent and creates another itself.

HUMAN IMPACT

FARMING THE OCEANS Seaweeds are harvested wild, but more are now grown in ocean nurseries and farms, especially in Asia. They are used for food, and seaweed extracts are used in a wide range of products—for example, in gels as a stabilizer, in cosmetics and pharmaceuticals, in beer-making, and as a fertilizer. SEAWEED HARVEST IN ZANZIBAR

Many seaweeds grow readily on floating rafts, as seen here. They flourish in strong light, away from grazing invertebrates, and provide vital income for coastal communities.

OCEAN LIFE

236

CHROMISTS INFRAPHYLUM DINOFLAGELLATA

Noctiluca scintillans DIAMETER HABITAT

Up to 1/16 in (2 mm)

Suface waters

DISTRIBUTION

Worldwide

Also known as sea sparkle, Noctiluca scintillans is a large, bioluminescent dinoflagellate that floats near the surface of the ocean, buoyed up by its oily cell contents. It is one of the naked dinoflagellates, which do not have a protective outer theca (shell). Like all dinoflagellates, it has two flagella but one is tiny. This species feeds on other plankton, and its second large flagellum helps sweep food particles toward it, which it then engulfs. Other dinoflagellates also feed in this way but there are many that are photosynthetic.

BIOLUMINESCENCE Floating just below the surface of the water at night, dinoflagellates, and in particular Noctiluca scintillans, are the most common cause of bioluminescence in the open ocean. Millions of Noctiluca scintillans cells twinkle in the waves, hence the common name sea sparkle. The blue-green light is emitted from small organelles within the cells and is generated by a chemical reaction. Unlike many bioluminescent fish, it does not depend on light-emitting bacteria.

INFRAPHYLUM DINOFLAGELLATA

Gymnodinium pulchelum DIAMETER HABITAT

0.025 mm

Surface waters

Temperate and tropical waters above continental shelves, and Mediterranean DISTRIBUTION

Some red-tide organisms such as Gymnodinium pulchellum produce toxins that affect the nervous system and the clotting properties of the blood, causing high mortality among fish as well as

invertebrates.The cause of red tides is not well understood but some scientists think they may be influenced by coastal pollution providing nutrients that might otherwise be in short supply and so normally limit the population size. Rapid reproduction by simple cell division results in huge numbers of Gymnodinium pulchellum being present in the water, turning it a characteristic brown-red color, as shown here in the seas around Hong Kong. Unlike many other types of dinoflagellate, this species lacks a test and also produces food by photosynthesis.

INFRAPHYLUM DINOFLAGELLATA

Neoceratium tripos

Strombidium sulcatum

LENGTH

0.2–0.35 mm

DIAMETER

HABITAT

Surface waters

HABITAT

DISTRIBUTION

Worldwide

0.045 mm

Surface waters

DISTRIBUTION

apical horn

lateral horns aid floatation

OCEAN LIFE

PHYLUM CILIOPHORA

The unique three-pronged shape of the dinoflagellate Ceratium tripos makes it easy to identify among the phytoplankton, where it is one of the dominant organisms. Although this species is usually solitary, several individuals may be seen together, attached to each other by the single apical horn. This occurs when a cell divides and the daughter cells remain linked in short chains. Ceratium tripos is sometimes parasitized by other protists.

Atlantic, Pacific, and Indian Oceans

Organisms such as Strombidium sulcatum are classified as ciliates because the cell membrane has many hairlike projections, called cilia, that are used in locomotion. In Strombidium sulcatum, the cilia are restricted to a collar at one end of its spherical body, which has no shell. Ciliates are the most complex of all protists and have two nuclei in their single cell, a macronucleus and a micronucleus. For most of the time Strombidium sulcatum reproduces asexually by splitting both nuclei and the cell into two. Periodically it must undergo a type of sexual reproduction called conjugation. Two individuals partially merge so that once the micronuclei have divided they can each obtain one part from the other. They then separate and each forms a new macronucleus from its micronucleus and then divides. Ciliates and dinoflagellates share some cell characteristics, and both belong to a group known as the alveolates.

CHROMISTS PHYLUM RADIOZOA

Cladococcus viminalis DIAMETER HABITAT

0.08mm

Surface waters

DISTRIBUTION

Mediterranean

Radiolarians produce extremely complex silica tests of spines and pores that are laid down in a well-defined

PHYLUM HAPTOPHYTA

Emiliania huxleyi DIAMETER HABITAT

0.006 mm

Surface waters

DISTRIBUTION

Atlantic, Pacific, and Indian Oceans

Emiliana huxleyi is a protist belonging to a group of haptophytes commonly known as coccolithophores. The name comes from a covering of intricately sculptured calcite plates called coccoliths with patterns that are unique to each species. Like some other protists, E. huxleyi can multiply

geometric pattern. The spines aid buoyancy and the pores provide outlets for cell material, called pseudopodia, which engulf any food that becomes trapped on the spines and carry it to the centre of the cell to be digested. Cladococcus viminalis is a polycystine radiolarian, which are the most commonly fossilized radiolarians and are frequently found in chalk and limestone rocks. very quickly in favorable conditions and form blooms that can cover areas of up to 38,600 square miles (100,000 square km). These blooms are visible from space because the coccoliths act like tiny mirrors and reflect sunlight so the water they are in appears a milky white. By reflecting light and heat and by “locking up” carbon in their calcite coccoliths, they help reduce ocean warming. They have been found worldwide in chalk deposits dating from 65 million years ago. The famous white cliffs of Dover in the UK are mainly formed from coccolith plates.

PHYLUM FORAMINIFERA

Hastigerina pelagica LENGTH 1/4 in HABITAT

(6 mm)

Warm waters at depth of 660 ft (200 m)

DISTRIBUTION Subtropical and tropical waters of North Atlantic and western Indian Ocean

Foraminiferans are unicellular organisms found only in marine habitats. Hastigerina pelagica is one of the larger forms. It is often pinkish red and has a calcareous test with several globular-shaped chambers from which radiate calcite spines

Ethmodiscus rex DIAMETER 1/16–1/8 in (2–3 mm) HABITAT

Warm, nutrient-poor water

DISTRIBUTION

Open ocean worldwide

Ethmodiscus rex is the largest of all diatoms and can be seen with the naked eye. It is a single cell with a rigid cell wall, called a test, which is impregnated with silica and covered in regular rows of pits. The test is made up of two disk-shaped halves, called valves, which fit tightly together. Because each diatom has a unique test, Ethmodiscus rex can be easily identified in the fossil record. It is found in rocks that date from the Pliocene and the fossils can be up to 5 million years old. The cells need to remain near the water surface in order to utilize the Sun’s energy for food, which they do by transforming the

PHYLUM OCHROPHYTA

Chaetoceros danicus LENGTH HABITAT

0.005–0.02 mm Surface waters Worldwide

First described in 1844, Chaetoceros is one of the largest and most diverse genera of marine diatoms, containing nearly 200 species. Chaetoceros danicus is a colonial form, and groups of seven cells are not uncommon (as shown here). It is easily recognized

globular-shaped chamber of calcareous test

Dictyocha fibula LENGTH

0.045 mm

HABITAT

Surface waters

Atlantic, Mediterranean, Baltic Sea, and eastern Pacific off coast of Chile DISTRIBUTION

The golden-yellow pigments visible in this image of Dictyocha fibula are typical of two groups of golden algae known as Chrysophyceae and Dictyochophyceae (this species). The word Dictyocha means “net” and refers to the large windows in the silica test. Fewer than 20 species of Dictyocha are alive today. They

products of photosynthesis into oily substances that increase their buoyancy. Ethmodiscus rex can reproduce sexually but, if conditions are favorable, it multiplies rapidly, simply by dividing into two. Over a 10-day period, one individual that divides three times a day can theoretically have more than 1.5 billion descendants.

valve forms one half of test

rigid cell wall (test)

are all that remains of a group of organisms that flourished more than 5 million years ago. Their fossils are abundant in some Miocene deposits. golden yellow pigments used in photosynthesis

projection from silica test

OCEAN LIFE

DISTRIBUTION

because it has highly distinctive long, stiff hairs, called setae, which project perpendicularly from the margins of its test. and have prominent secondary spines along their length. Chloroplasts, which contain pigments used in photosynthesis, are numerous and found inside both the cell and the setae. The setae are easily broken and if large quantities lodge in the gills of a fish, they may kill it. The secondary spines anchor the setae to the sensitive gill tissue causing irritation, and the fish reacts by producing mucus. Eventually, it dies from suffocation.

covered with cytoplasmic strands (pseudopodia) for collecting food. Hasterigina pelagica is unique in surrounding its test with a gelatinous capsule of tiny frothy bubbles, which is thought to aid buoyancy. Dinoflagellates sometimes live on the surface of the capsule and up to 79 have been counted on a single individual, although 6–10 is more usual. The relationship between the two organisms is not clearly understood because Hasterigina pelagica is carnivorous, yet the dinoflagellates are unharmed.

calcite spines aid buoyancy

PHYLUM OCHROPHYTA

PHYLUM OCHROPHYTA

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238

CHROMISTS PHYLUM OCHROPHYTA

Limey Petticoat Padina gymnospora HEIGHT

Up to 10cm (4in)

Rock pools and shallow subtidal rocks

HABITAT

WATER TEMPERATURE

20–30˚C (68–86˚F) DISTRIBUTION Coasts in tropical and subtropical areas worldwide

Padina is the only genus of brown seaweeds to have calcified fronds, hence this species’ common name of Limey Petticoat. The reflective chalk shows as bright white concentric bands on the upper surface of the fan-shaped fronds. The fronds are only 4–9 cells thick and curled inwards. Older fronds may become split into wedge-shaped sections. This species is widespread in tropical seas, often growing in masses on shallow subtidal rocks, and on old coral and shells.

PHYLUM OCHROPHYTA

Giant Kelp Macrocystis pyrifera LENGTH

45m (150ft)

Rocky sea beds, occasionally sand

HABITAT

WATER TEMPERATURE

5–20˚C (41–68˚F) Temperate waters of southern hemisphere and northeastern Pacific

DISTRIBUTION

Giant Kelp (pictured on pp.240–41) is the largest seaweed on Earth. It can grow at the rate of 60cm (24in) per day in ideal conditions, and reaches lengths of over 30m (100ft) in a year. Giant

PHYLUM OCHROPHYTA

Oyster Thief Colpomenia peregrina DIAMETER

Up to 10cm

(4in) Intertidal and subtidal rocks and shells

HABITAT

WATER TEMPERATURE

6–28˚C (49–83˚F) Coasts of western North America, Japan, and Australasia; introduced in Atlantic

DISTRIBUTION

The Oyster Thief gets its unusual name from its habit of growing on shells, including commercially grown oysters. The frond is initially spherical and solid, but as it grows, it becomes irregularly lobed and hollow and fills with gas. Sometimes, this can make it sufficiently buoyant to lift the oyster,

PHYLUM OCHROPHYTA

PHYLUM OCHROPHYTA

Landlady’s Wig

Sea Palm

Desmarestia aculeata LENGTH

Postelsia palmaeformis Up to 1.8m (6ft)

LENGTH

Up to 60cm

(24in)

Subtidal rocks, and kelp forests

HABITAT

HABITAT

Wave-exposed

shores

WATER TEMPERATURE

0–18˚C (32–64˚F)

WATER TEMPERATURE

8–18˚C (46–64˚F) DISTRIBUTION

Near coasts in temperate, cold, and

DISTRIBUTION

West Coast of North America

polar regions

OCEAN LIFE

This large seaweed has narrow brown fronds with many side-branches. Its bushy appearance is the reason for its common name of Landlady’s Wig. The smallest branches are short and spinelike, hence the species name aculeata, which means “prickled”. In summer, the whole plant is covered with delicate branched hairs. This species is particularly abundant on boulders and in kelp forests disturbed by waves.

Sea Palms are kelps, which are large brown seaweeds that belong to the order Laminariales, as does Giant Kelp (above). Unusually for a kelp, Sea Palm grows on the midshore, where it forms dense stands on wave-exposed coasts. It has a branched holdfast, and a stout, hollow stalk, which stands erect when the tide is low. The top of the stalk is divided into many short, cylindrical branches, each of which bears a single frond up to 25cm (10in) long, with toothed margins and deep grooves running down both faces. Spores are released into the grooves and drip off the frond tips onto the holdfasts and nearby rocks at low tide, so that the developing seaweeds grow as dense clumps. Some Sea Palms attach to mussels and are later ripped off during storms, making more rock available for other Sea Palms to grow.

Kelp normally grows at a depth of 10–30m (30–100ft), but it can grow much deeper in very clear water. The huge branched holdfast, which is about 60cm (24in) high and wide after three years, is firmly attached to the sea bed. From it, a number of stalks (or stipes) stretch towards the surface, bearing many strap-like fronds, each buoyed by a gas-filled bladder. The stem and fronds continue to grow on reaching the surface, floating as a dense canopy. Giant Kelp has a two-phase life cycle. Fronds (sporophylls) at the base of the kelp produce spores that develop into tiny creeping filaments. The filaments produce eggs and sperm, which combine to produce embryonic kelp plants. which is not fixed to the sea bed, and they may both be carried away by the tide. This seaweed has a thin wall with only a few layers of cells. The outer layer is made of small, angular cells which contain the photosynthetic pigments that give the Oyster Thief its brown colour.

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CROFTER’S WIG In very sheltered bays and sea lochs, detached pieces of “normal” Knotted Wrack will continue to grow, lying loose on the sea bed. In situations where the fronds are alternately covered by salt and fresh water, they divide repeatedly to form a dense ball that has no bladders or reproductive structures. This unattached form, which is known as Crofter’s Wig, appears very different to the attached form, even though it is genetically identical.

PHYLUM OCHROPHYTA

Knotted Wrack Ascophyllum nodosum LENGTH

Up to 3m (10ft)

Sheltered seashores

HABITAT

WATER TEMPERATURE

0–18˚C (32–64˚F) DISTRIBUTION Coasts of northwestern Europe, eastern North America, and north Atlantic islands

PHYLUM OCHROPHYTA

Neptune’s Necklace Hormosira banksii LENGTH

Up to 30cm

(12in) Lower shore and subtidal rocks

HABITAT

WATER TEMPERATURE

10–20˚C (50–68˚F) Coasts of southern and eastern Australia and New Zealand DISTRIBUTION

Knotted Wrack belongs to a group of tough brown seaweeds that often dominate rocky seashores in cooler climates. It is firmly attached to the rocks by a disc-shaped holdfast, from which arise several narrow fronds that often grow to 1m (3ft) in length, and exceptionally to 3m (9ft) in very sheltered situations. Single oval bladders grow at intervals down the frond. The fronds produces about one bladder a year, so the seaweed’s age can be roughly estimated by counting

PHYLUM OCHROPHYTA

Japweed Sargassum muticum LENGTH

2–10m

(6–33ft) Intertidal and subtidal rocks and stones

HABITAT

WATER TEMPERATURE

5–26˚C (41–79˚F) Coasts of Japan, introduced in western Europe and western North America DISTRIBUTION

Japweed can reproduce all year round and forms dense stands in quiet waters. Native to Japan (hence its common name), it was accidentally introduced to western North America and Europe, and is steadily expanding its range in these areas. It outcompetes other seaweeds and in these regions is regarded as an invasive species. This long, bushy seaweed has numerous side-branches, which have many leaflike fronds up to 10cm (4in) long. The fronds bear small, gas-filled bladders, either singly or in clusters.

OCEAN LIFE

Neptune’s Necklace is one of the many brown seaweeds endemic (unique) to New Zealand and the cooler waters around Australia. Its distinctive fronds, which look like a string of brown beads, are made up of chains of ovoid, hollow segments joined by thin constrictions in the stalk. Small reproductive structures are scattered over each “bead”. Dense mats composed almost entirely of this one species can be found on seashore rocks. The fronds are attached to the rock by a thin, disc-shaped holdfast. Neptune’s Necklace also lives unattached among mangrove roots. The shape of its segments varies according to habitat. They are spherical and about 2cm (3/4 in) wide in fronds growing on sheltered rocks, mussel beds on tidal flats, or in mangrove swamps. Fronds growing on subtidal rocks on moderately exposed coasts have smaller segments that are just 6mm (1/4 in) long.

a series of bladders. The bladders hold the fronds up in the water so that they gain maximum light, which is an advantage in the often turbid waters where Knotted Wrack grows. This also makes it harder for grazing snails to reach the fronds when the tide is in. The dark brown fronds may be bleached almost to yellow in summer. Reproductive structures that look like swollen sultanas are borne on short side-branches, and orange eggs can sometimes be seen oozing from them.

GIANT KELP

This enormous seaweed can grow at a rate of 20 in (50 cm) per day in favorable conditions, such as the relatively cold water off California (shown here). Air bladders help keep the kelp’s blades afloat as they grow upward toward the surface, where there is an enhanced supply of light and nutrients.

242

PLANT LIFE

Plant Life

HUMAN IMPACT

BEACH PLANTS

PLANTS FORM A GREAT

kingdom of life-forms, all of which use the pigment chlorophyll to KINGDOM Plantae fix carbon dioxide from the atmosphere into SPECIES 315,000 organic molecules, using energy from sunlight. Most organisms in the plant kingdom are “higher” plants, which evolved on land and remain land-based. Of these, several unrelated families of flowering plants (see p.250) have since returned to the sea or taken up residence on the coast. The plant kingdom, as defined in this book, also encompasses more primitive organisms that first evolved in water—the microscopic green algae (microalgae) and the green and red seaweeds (macroalgae). Brown seaweeds appear very similar but may not be closely related to true plants and are classified in this book in the phylum Chromista (see p.236). DOMAIN Eucarya

Marine Plant Diversity

TEMPERATE MARINE PLANTS

dune flower

mangrove tree

The sand crocus of the Canary Islands grows only in a few coastal locations on Lanzarote and Fuerteventura. It is protected, but threatened by tourism development.

Seagrasses are abundant in tropical lagoons, and green seaweeds include calcified species. Mangroves line estuaries and creeks, and other flowering plants, including shrubs and trees, colonize the back of sandy beaches. Although not shown here, seaweeds may grow seasonally on rocky shores.

H AC

BE

P

M WA ES

coconut palm

V RO

NG

MA

high tide mark intertidal zone of beach mermaid’s wine glass alga, Acetabularia

sea campion

S

NE

DU

SAND CROCUS

TROPICAL MARINE PLANTS

Plants are united by their use of chlorophyll for photosynthesis. The higher plants include several major land-based groups, including ferns and conifers. Because higher plants evolved on land, they are adapted to life in air and to fresh water. They have tissues bearing vessels that transport water and food. Of the higher plants, it is mainly the flowering plants (the largest group) that have invaded marine habitats. Along with mosses, they inhabit the coastal fringes, with only the seagrasses being fully marine. Green seaweeds and microscopic green algae (microalgae) lack stems and roots, have neither woody tissues nor transport vessels, and are mostly aquatic. Temperate seas are rich in phytoplankton, including green algae. Green algae commonly grow on rocks and red algae on mud flats. F LIF Seagrasses have true roots AC E and live in sediment in the S shallow subtidal and intertidal zones, and in brackish lagoons. Above high water, cliffs, sand dunes, and salt marshes are home to flowering plants, mosses and lichens.

Beach plants grow in places used by humans for recreation. We can coexist, especially when people use paths in coastal dune areas. In fact, paths maintain low-growing plants, such as mosses, which might otherwise become overgrown. However, fragile dunes are damaged by erosion, and plants that grow only in a limited strip of coastal habitat are highly vulnerable to human development.

Halophila sea grass clear water with few algae

moss

SH

marram grass

OR

E

red seaweeds on intertidal rocks

Caulerpa seaweed green seaweeds on intertidal rocks

thrift

SH AR

TM AL

S

LA GO

ON

sea lettuce seaweed on boulders and bedrock

CO

RA

LR

EE

F

red seaweeds in subtidal zone Codium seaweed on boulders and bedrock

OCEAN LIFE

brackish lagoon

SEA ROCKET

Ulva seaweed in channel sea rocket above high tide intertidal zone

ED

ER ELT H -S E MI OR SE SH

eelgrass in sediment in subtidal zone surface water thick with green microalgae

ED ER ELT RE H S HO S

D SE PO RE X E O SH

A European member of the brassica family, sea rocket can grow on pure sand, just above high tide, where it traps sand, forming small foredunes. Its waxy leaves repel sea spray, while its stubby fruit pods are dispersed by the tide.

PLANT LIFE

243

Above High Water

PLANTS OF SHIFTING SHORES

Sea mayweed, with daisylike white flowers, and oyster plants, with their dark blue-green leaves, are salt-tolerant flowering plants that grow on semi-sheltered shores of shingle.

Above the reach of the highest tides, the environment is essentially terrestrial, but its proximity to the sea makes life hard for all but a few specialized flowering plants and lichens. In places, the coast is covered with dunes of sand blown from the seashore. Dunes are often alkaline, being rich in calcium carbonate from marine shells and maerl (see p.245). With few nutrients, dunes only support hardy colonizers tolerant of infertile and salty soil. Acidic dunes made from sand with little shell support many lichens and mosses such as golden dune moss. Marram, a grass with a fast-growing root and rhizome network stabilizes dunes and takes the first steps toward soil formation. Plants that can fix nitrogen in root nodules, such as the casuarina tree, have an advantage here. On rocky cliffs plants are safe from grazing animals but must withstand salty spray, drying winds and scanty soil. Plants such as sea campion have very long roots that reach deep into rock crevices for water draining from the land. Plants with succulent leaves and waxy cuticles can store the water they find.

ABOVE AND BELOW THE TIDE LINE

Marine plants range from coastal trees growing above the high tide mark, such as the Coconut Palm, to seagrasses, the only wholly aquatic marine flowering plants, below it.

Between the Tides Plants between the tides have to live both in and out of water in variable conditions sometimes hot, dry, and salty, and at other times drenched with cold, fresh rainwater. Intertidal zones support green and red seaweeds, seagrasses, and mangroves. Many green seaweeds are tolerant of brackish water and grow down the upper shore in strips following freshwater seeps and streams. Lower down, delicate red seaweeds thrive in pools or in the damp beneath tough brown seaweeds. Many are ephemeral, growing quickly in fair conditions and dispersing many spores. They may quickly cover tropical coasts where monsoons bring humid conditions, but then dry up and blow away when the sun returns. Seagrasses grow on lower intertidal flats; here the sediments retain moisture until the tide returns. In the tropics, mangroves colonize intertidal sediments, but only their roots are regularly submerged, while the rest of the plant remains in the air. In colder climates, salt-marsh vegetation develops on mudflats.

SUBMERGED SALT MARSH

The salt-tolerant sea pink grows in salt marshes, which develop on sheltered coasts in temperate regions. Like other salt-marsh plants, the sea pink is submerged only in the highest tides.

Aquatic Plants

OCEAN LIFE

Only microalgae, seaweeds, and seagrasses live permanently submerged in seawater. All seaweeds can absorb nutrients and gases over their whole body surface, so they do not need the transport systems of land plants, and their holdfast simply attaches them to the seabed. Seagrasses have a land-plant anatomy, so they need extra structures such as air spaces (lacunae) to aid gas exchange. Plants living in seawater can only thrive in the top few yards, because enough light for SEAWEED BED photosynthesis cannot Green seaweeds in the English Channel include penetrate beyond this. Codium (in the foreground) Many marine plants are and sea lettuce (lower right). tough to deter grazing They are growing here with animals or produce toxic an unrelated brown seaweed called serrated wrack. or distasteful chemicals.

244

RED SEAWEEDS

Red Seaweeds RED SEAWEEDS

are attractive marine plants and are found KINGDOM Plantae in shallow seas around DIVISION Rhodophyta the world. Their red color CLASSES 2 or more comes from the extra SPECIES 6,394 pigments they have in addition to green chlorophyll. While they appear to be plants, they differ in some cellular details and metabolism. Many scientists do not consider them to be true plants, but there is as yet no full consensus. DOMAIN Eucarya

Anatomy

Habitats and Distribution On the shore, red seaweeds mostly live at the lowest levels where they are less likely to dry out. In deeper water their additional pigments allow them to flourish in the dim blue light that remains and they extend deeper than brown and green seaweeds. Red (and brown) seaweeds are less abundant in tropical waters, an exception being the red oralline encrusting seaweeds, which play a very important role in cementing coral reefs.

BARBED COLONIZER

This red seaweed has barbed branches enabling detached fragments to hook onto other organisms and even ships’ hulls. It disperses in this way and has been transported outside its native range.

DULSE

The shape and form of red seaweeds is highly diverse but in general they are relatively small and delicate. Like green and brown seaweeds most have a holdfast, stipes (stems) and fronds that absorb water, nutrients, and sunlight. Coralline seaweeds have a heavily calcified frond, which is too hard for most grazers to eat. They look more like pink crusts or small corals than plants. Maerl forms unattached nodules that resemble twiggy coral lying on the seabed. Some red seaweeds have two phases, growing as a tiny long-lived crust and as an annual bushy frond. These look so different they were first described as separate species.

Red seaweeds rely on moving water to bring them nutrients and oxygen. The fingerlike fronds of this dulse increase its surface area while preventing it from tearing in rough conditions.

midrib

frond

stipe

holdfast

PERENNIAL SPECIES

This beautiful red seaweed is called sea beech. It grows new fronds each year from a perennial stipe, and reproduces from spores in winter.

DIVISION RHODOPHYTA

Small Jelly Weed Gelidium foliaceum LENGTH

2 in (5 cm) HABITAT

OCEAN LIFE

Intertidal rocks WATER TEMPERATURE

50–68˚F (10–20˚C) Coasts of southern Africa and southern Japan

DISTRIBUTION

There are many species of Gelidium worldwide, and they are difficult to identify because the plants can look very different depending on their habitat and whether they have been

grazed by seashore animals such as limpets. Ongoing work on molecular sequencing is gradually resolving some of these problems, and Gelidium foliaceum is one species that has recently been reclassified. It has a flattened, much lobed and curled frond, which grows in dense clumps on rocky seashores.The fronds are tough and cartilaginous, and the seaweed is attached to the rock at frequent intervals by small hairlike structures, or rhizoids, from a creeping stem, or stolon. This creeping habit is probably the main method of spreading, but some species of Gelidium also reproduce sexually. Some Gelidium species are a source of the gelatinous substance agar, which is used in cooking and microbiology.

RED SEAWEEDS DIVISION RHODOPHYTA

Laver Porphyra dioica LENGTH

Up to 20 in (50 cm) HABITAT

Intertidal rocks WATER TEMPERATURE

43–64˚F (6–18˚C) DISTRIBUTION Coasts of northeastern and western Europe and Mediterranean around Italy

DIVISION RHODOPHYTA

Irish Moss Mastocarpus stellatus LENGTH

7 in (17 cm)

Lower shore and subtidal rocks

HABITAT

WATER TEMPERATURE

32–77˚F (0–25˚C) Coasts of northeastern North America, northwestern Europe, and Mediterranean DISTRIBUTION

This tough red seaweed is common on exposed shores, often forming a dense turf on the lower shore. Its frond is attached to rock by a disk-shaped holdfast, from which arises a narrow stipe (stalk) that gradually expands

This species of red seaweed has only recently been separated from the very similar P. purpurea on the basis of how they reproduce. P. dioica is dioecious (male and female reproductive cells are on separate fronds), while P. purpurea is monoecious (male and female reproductive cells are on the same frond). P. dioica grows on intertidal, sandy rocks and is most abundant in the spring and early summer. The membranous frond is only one cell thick and is olive-green to purple-brown or blackish. This species appears to have a limited distribution in western Europe, but the genus is widespread throughout the world. All species of Porphyra are edible and are often harvested for food worldwide, especially in Japan where they are cultivated and known as nori. In the UK, wild laver is collected and made into the Welsh delicacy laverbread. into a divided blade, which is slightly rolled to form a channel with a thickened edge. Reproductive structures housed in small nodules on the blade’s surface produce a very different seaweed in the form of a thick black crust (it was originally named Petrocelis cruenta because it was thought to be an entirely different species). Spores from this crust grow back into the erect form, in a typical two-phase life history. Mastocarpus stellatus and the similar Chondrus crispus are both known as Irish moss or carrageen moss and are collected on an industrial scale on both sides of the north Atlantic to produce the gelling agent carrageenan.

DIVISION RHODOPHYTA

245

DIVISION RHODOPHYTA

Maerl

Cotton’s Seaweed

Phymatolithon calcareum DIAMETER

Kappaphycus alvarezii

Up to 23/4 in

LENGTH

(7 cm)

20 in (50 cm)

Intertidal and shallow subtidal rocks

HABITAT

Subtidal seabed sediments

HABITAT

WATER TEMPERATURE

50–86˚F (10–30˚C)

WATER TEMPERATURE

32–77˚F (0–25˚C) DISTRIBUTION Coasts of Atlantic islands, northern and western Europe, Mediterranean, and Philippines

The term “maerl” describes various species of unattached coralline seaweeds that live on seabeds. Phymatolithon calcareum forms brittle, purple-pink, branched structures that look more like small corals than seaweed. It grows as spherical nodules at sheltered sites, or as twigs or flattened medallions at more exposed sites. In places with some water movement from waves and tides, but not enough to break the maerl nodules, extensive beds can develop. Maerl is as much a habitat as a species, and both the living maerl and the maerl-derived gravel beneath it harbour many small animals. Maerl grows slowly and the beds are vulnerable to damage from bottom trawlers.

DIVISION RHODOPHYTA

Coral Weed

DISTRIBUTION Coasts of Africa, southern and eastern Asia, and Pacific islands

Formerly called Eucheuma cottonii, this is a much-branched, cylindrical red seaweed that is farmed extensively in the Philippines for extraction of carrageenan, a gelling agent similar to agar (see panel opposite). In the wild, it grows attached to rocks or lies loose in sheltered places. Like some other red seaweeds, its fronds are often shades of green and brown rather than red.

Corallina officinalis LENGTH

Up to 43/4 in

(12 cm) Rock pools and shallow subtidal rocks

HABITAT

WATER TEMPERATURE

DIVISION RHODOPHYTA

Spectacular Seaweed Drachiella spectabilis

32–77˚F (0–25˚C) DISTRIBUTION

LENGTH

Up to 21/2 in

(6 cm)

Coasts worldwide except for far north

and Antarctica

Subtidal rocks at 6–100 ft (2–30 m)

HABITAT

WATER TEMPERATURE

46–64˚F (8–18˚C) Off western coasts of Scotland, UK, Ireland, France, and Spain DISTRIBUTION

OCEAN LIFE

Coral weed belongs to a group of red seaweeds known as coralline seaweeds, which have chalky deposits in the cell walls that give them a hard structure. Coral weed fronds have rigid sections that are separated by flexible joints. The branches usually lie in one plane, forming a flat, featherlike frond, but the shape is very variable. On the open shore, the fronds are often stunted, forming a short mat a few inches high in channels and rock pools and on wave-exposed rocks. These mats often harbor small animals, and other small red seaweeds attach to the hard fronds. Subtidally, the fronds grow much longer. The color of coral weed varies from dark pink when it lives in the shade to light pink in sunny locations. When the seaweed dies, its hard white skeleton becomes part of the sand.

This colorful seaweed is rarely seen, except by divers, because it normally grows in relatively deep water and is rarely washed ashore. It also grows in shallower water within kelp forests. It has a thin, fan-shaped frond, split into wedges, that spreads out over the rock and reattaches with small rootlike structures called rhizoids.Young plants have a purple-blue iridescence, which is lost as the seaweed ages. Sexual reproduction is unknown in this species and spores are produced asexually.

246

PLANT LIFE

Green Seaweeds

frond

GREEN ALGAE LARGE ENOUGH

to be seen with the naked eye are known as green seaweeds. They are classified with the microscopic green algae, or microalgae (see p.248). True plants of the sea, they have pigments and other features in common with higher plants. They can be abundant in tropical lagoons, and proliferate seasonally on many temperate seashores. Ulva (sea lettuce) is grown for food.

DOMAIN Eucarya KINGDOM Plantae DIVISION Chlorophyta CLASSES About 8 SPECIES 5,426

Habitats

Anatomy

Green seaweeds often attach to rocks on rocky coasts, particularly in temperate and cold waters, and are ephemeral colonizers in seasonally disturbed tidal and shallow subtidal habitats. Ulva species, such as sea lettuce, dominate in high-level rock pools, or where fresh water seeps over the shore, since they can withstand changes in saltiness and temperature. The more delicate Cladophora and Bryopsis species live in rock pools or among red and brown seaweeds in the shallow subtidal zone. Green seaweeds also thrive in shallow, tropical lagoons, where species of Caulerpa, Udotea, and Halimeda are often abundant. Caulerpa species have runners (stolons), which creep through sand or cling to rock, while the bases of Udotea and Halimeda are a bulbous mass of fibers that anchor in sand. Halimeda (cactus seaweed) is heavily encrusted with calcium carbonate, which breaks up when the plant dies, contributing to the lagoon sand.

The body structure of green seaweeds lacks stems and roots. Green seaweed shapes range from threadlike (filamentous) to tubes, flat sheets, and more complex forms. Their bright green color is due to the fact that their chlorophyll is not masked by additional pigments, unlike red and brown seaweeds. Many of the features of green algae, including their types of chlorophyll, are shared by higher plants (mosses, liverworts, and vascular plants), so green seaweeds appear to be more closely related to higher plants than to red and brown seaweeds.

large, fibrous holdfast

SEAWEED BODY PARTS

Green seaweeds have a simple structure, with an erect frond and a disk-shaped or fibrous holdfast. This tropical Udotea species has calcified fronds with many branched siphons. FRAGILE FRONDS

This delicate Bryopsis plumosa has coenocytic fronds, meaning its fronds do not have the crosswalls common in other green seaweeds.

CODIUM FOREST

This mini-forest of Codium fragile is growing on shallow rocks in a sheltered bay in Scotland. The fronds are buoyant, holding the plants up to the light.

FLEXIBLE SEAWEED

Able to handle fluctuations in salinity and temperature, Ulva species thrive in this freshwater stream as it flows across the seashore.

CLASS ULVOPHYCEAE

Flaccid Green Seaweed Ulothrix flacca SIZE

Up to 4 in (10 cm)

Intertidal on various shore types

HABITAT

HABITAT

CLASS ULVOPHYCEAE

Sea Lettuce Ulva lactuca SIZE

Up to 40 in (100 cm)

Intertidal and shallow subtidal

HABITAT

WATER TEMPERATURE

32–86˚F (0–30˚C)

32–68˚F

(0–20˚C)

OCEAN LIFE

attached to its rock by a single cell called a basal cell, which may be given additional anchorage by outgrowths called rhizoids. This seaweed reproduces by releasing up to a hundred gametes, each with two flagellae, from some of the cells. In another phase of its life cycle it is a single globular cell.

DISTRIBUTION Northern Atlantic, Mediterranean, waters off South Africa, Pacific

This seaweed is made up of many unbranched green filaments, which themselves consist of strings of cells. The filaments form soft, woolly masses or flat green layers that stick to intertidal rocks. Each filament is

DISTRIBUTION

Coastal waters worldwide

Sea lettuce is common worldwide on seashores and in shallow subtidal areas, growing in a wide range of conditions and habitats. Its frond is a bright green, flat sheet, which is often split or divided, and has a wavy edge. The plant is very variable in shape and size, ranging from short, tufted plants on exposed shores to

sheets over a yard long in sheltered, shallow bays, especially where extra nutrients are available in polluted harbors. Sea lettuce reproduces by releasing gametes from some cells, and it can also spread vegetatively by regeneration of small fragments. Large fronds lying on the seabed may be full of holes made by grazing animals. It is a also popular food for humans in many parts of the world.

GREEN SEAWEEDS CLASS CLADOPHOROPHYCEAE

Giant Cladophora Cladophora mirabilis LENGTH

Up to 40 in (100 cm) HABITAT

Subtidal rocks and kelp WATER TEMPERATURE

50–59˚F (10–15˚C) DISTRIBUTION

Southern Atlantic off southwest

Africa

CLASS BRYOPSIDOPHYCEAE

Sea Grapes Caulerpa racemosa HEIGHT

Up to 12 in (30 cm) HABITAT

Shallow sand and rock WATER TEMPERATURE

59–86˚F (15–30˚C) CLASS CLADOPHOROPHYCEAE

Sailor’s Eyeball Valonia ventricosa SIZE

Up to 11/2 in (4 cm)

Rock and coral to 100 ft (30 m)

HABITAT

WATER TEMPERATURE

50–86˚F (10–30˚C) DISTRIBUTION Western Atlantic, Caribbean, Indian and Pacific oceans

CLASS BRYOPSIDOPHYCEAE

This odd seaweed looks like a dark green marble, and consists of a single large cell attached to the substrate (which is often coral rubble) by a cluster of filaments called rhizoids. Younger plants have a bluish sheen, but older ones become overgrown with encrusting coralline red seaweeds. Sailor’s eyeball has an unusual way of reproducing vegetatively: daughter cells are formed within the parent, which then degenerates, releasing the young plants in the process.

DISTRIBUTION

Warm waters worldwide

247

A giant among Cladophora species, C. mirabilis grows to 40 in (1 m) long. It is bluish green and filamentous, with many straggly side-branches. It is made up of strings of cells, but individual cells in the main axis may be 1/2 in (12 mm) long. The plant attaches using a disk made of interwoven extensions of its basal cell, and often has red algae growing on it. It has a very limited distribution in South Africa, but other species of Cladophora are common worldwide.

KILLER SEAWEED A strain of Caulerpa taxifolia that is widely used in marine aquariums is an invasive species. It is toxic to grazers, grows rapidly, and forms a dense, smothering carpet on the seabed. In 1984 it was discovered in the Mediterranean off Monaco, and has since spread rapidly along the coast, altering native marine communities.

This seaweed has creeping stolons (stems) that anchor it to rocks or in sand, and from which arise upright shoots covered with round sacs, or vesicles, hence the common name sea grapes. Each plant is a single huge cell. Old plants may become densely branched and entangled, growing to 6 ft (2 m) across. There are many varieties of sea grapes, and around 60 species of Caulerpa worldwide.

CLASS BRYOPSIDOPHYCEAE

Cactus Seaweed

Velvet Horn

Halimeda opuntia

Codium tomentosum SIZE

SIZE

Up to 10 in (25 cm)

Up to 8 in (20 cm)

Intertidal pools, shallow subtidal rocks HABITAT

HABITAT

Rock and sand

WATER TEMPERATURE

46–86˚F (8–30˚C)

WATER TEMPERATURE

68–86˚F (20–30˚C) DISTRIBUTION

Red Sea, Indian Ocean, and western

DISTRIBUTION

Coastal waters worldwide

Pacific

CLASS DASYCLADOPHYCEAE

Mermaid’s Wineglass Acetabularia acetabulum SIZE

11/4 in (3 cm)

calcium carbonate, and it terminates in a small cup. The cup is made up of fused rays that produce reproductive cysts. The cysts are released after the remainder of the plant has decayed, and they then require a period of dormancy in the dark before they begin to germinate.

HABITAT

Shallow subtidal rocks WATER TEMPERATURE

50–77˚F (10–25˚C) Eastern Atlantic off North Africa, Mediterranean, Red Sea, Indian Ocean DISTRIBUTION

This curious little green alga grows in clusters on rocks or shells covered with sand in sheltered parts of rocky coasts within its range. Although it grows to 11/2 in (3 cm), it consists of just one cell. Its calcified frond appears white because it is encrusted with

OCEAN LIFE

The heavily calcified skeletons of species of Halimeda contribute much of the calcareous sediment in the tropics. The plant consists of strings of flattened, kidney-shaped, calcified segments, linked by uncalcified, flexible joints. By day, its chloroplasts are in the outer parts of the frond; at night they withdraw deep into the plant’s skeleton. This, along with sharp crystals of aragonite, and the presence of toxic substances in the frond, protects them from nocturnal grazing.

The spongy fronds of velvet horn are made up of interwoven tubes, arranged rather like a tightly packed bottlebrush, with each tube ending in a swollen bulb. Many of these bulbs packed together make up the outside of the frond, which is usually repeatedly branched in two. Many short, fine hairs cover the seaweed, giving it a fuzzy appearance when in water. The plants are attached to rocks by a spongy holdfast. Although this seaweed is present year-round, its maximum development is in winter, and it also reproduces during the winter months.Velvet horn, like all Codium species, is often grazed by sacoglossans, small sea slugs that suck out the seaweed’s contents, but can keep the photosynthetic chloroplasts alive and use them to make sugars inside their own tissues. The chloroplasts color the sea slugs green, which helps to disguise them from predators. There are about 50 species of Codium.

248

PLANT LIFE

Green Algae

Anatomy

THESE MICROSCOPIC, MOSTLY single-celled

DOMAIN Eucarya KINGDOM Plantae

plants live in the surface layers of the ocean in CLASS Prasinophyceae immense numbers, and SPECIES 200 they form an important part of the phytoplankton (see p.212). Sometimes referred to as the “grasses of the sea,” like most plants, they produce their own food through photosynthesis. Large green algae, visible to the naked eye, are called green seaweeds and are discussed elsewhere in this book (see p.246). Microscopic algae are often termed “microalgae.” Green microalgae are frequently classified as protists. Numerous other groups of protists (see p.236) are also termed algae, and also live as phytoplankton. DIVISION Chlorophyta

Habitats With a few exceptions, marine microalgae swim and float, in countless millions, in the sunlit layers of the ocean so that photosynthesis can occur. They are more numerous in nutrient-rich waters, such as those benefiting from coastal runoff. In temperate coastal waters, green microalgae multiply rapidly each spring in response to rising nutrient and light levels, creating abundant food for zooplankton. Such population explosions, or blooms, can reduce the water clarity for weeks. Some green algae live inside the bodies of animals (see panel, right) and inside protist plankton—in the appendages (rhizopoda) of radiolarians (see p.237) and within compartments inside the dinoflagellate Noctiluca (see p.236).

HALOSPHAERA

These microalgae (shown greatly enlarged) are green with chlorophyll and bear hairlike swimming appendages called flagellae.

Marine microscopic green algae mostly belong to a class of algae called the Prasinophyceae. Each consists of a single living cell that is generally too small to be visible to the naked human eye. Even the larger species, such as members of the genera Halosphaera and Pterosperma, measure just 0.1–0.8 mm across, so appear as no more than a speck. Some green algae can swim, and beat two or more hairlike structures, called flagellae, to move through the water. Others lack flagellae and cannot propel themselves. Several groups of these plants have a two-stage life history, including both swimming and non-swimming forms. All green algae possess chloroplasts—structures GREEN BEACHES that contain the green pigment chlorophyll A few green algae and worms form symbiotic partnerships, in that plants use in which both species gain. The photosynthesis. beach-living worms ingest algae, giving them a green color. At low tide, they move up through the sand to pools on the surface, where the algae photosynthesize. In return, the worms absorb food from the algae.Vast numbers of the worms tinge beaches green.

ANIMAL–ALGA PARTNERSHIP

When young, these marine flatworms ingest green algae, which may multiply until there are 25,000 algal cells living in each worm. The adult worms obtain all their nutrition from the algae.

GREEN TIDE

Green algae grow quickly and are the first to respond in spring when nutrients become available. While grazer levels are low, the algae are free to multiply until their density turns the ocean green.

CLASS PRASINOPHYCEAE

Halosphaera viridis SIZE

20–30 micrometers (motile phase)

CLASS PRASINOPHYCEAE

Tetraselmis convolutae SIZE

10 micrometers

OCEAN LIFE

DISTRIBUTION

Northeastern Atlantic, eastern Pacific

Halosphaera viridis is a small, pearshaped cell with four swimming flagellae at one end. It reproduces by splitting in two, allowing it to reach high concentrations and from time to time some cells become small cysts whose contents divide into small disks. Each disk eventually becomes a flagellated cell that will be released into the sea. There can be hundreds of cysts per square yard in the open ocean, and they are probably a vital food source for larger zooplankton.

Northeastern Atlantic, off the western coasts of Britain and France

DISTRIBUTION

Although it can survive free-living, the tiny cells of Tetraselmis convolutae often live inside a worm host (see box, above) in a symbiotic relationship.The worm provides them with shelter and a constant environment inside its body.The worm’s light-seeking behavior gives the algae ideal conditions for photosynthesis, which in turn provides both algae and worm with nutrients and energy.

MOSSES

Mosses

249

Anatomy MOSSES ARE LOW-GROWING

plants that thrive in damp habitats on land, KINGDOM Plantae where they may carpet the ground or DIVISION Bryophyta rocks. They dislike salty environments SPECIES 13, 365 and only a few species manage to live in the intertidal zone of coasts, mainly in cooler climates. A much wider variety of mosses can be found slightly farther inland, away from the direct effects of sea spray but within range of moisture-laden sea mists. DOMAIN Eucarya

Most mosses have a recognizable structure of stems and leaves, which, as in other plants, gather sunlight and perform photosynthesis. However, unlike flowering plants (see p.250), they do not have woody tissues for support, and they also lack the conducting tissues that transport water and nutrients. Mosses have a very thin outer layer of cells, or cuticle, that can absorb (and lose) water, nutrients, and gases over their entire surface. Their “roots” are simple strands called rhizoids, which anchor the plant to its growing surface. Mosses SPORE PRODUCTION reproduce sexually by means of Mosses have low-growing leaves, but sprout wind-blown spores, or asexually taller structures with bulbous tips called capsules, from which spores are released. by spreading across the ground.

Habitats Mosses generally prefer moist, shady places and are most numerous in the cooler and damper climates of temperate regions. This is because they lack the thick cuticle that enables other types of plant to retain moisture. Without the protection of this skinlike surface, mosses soon shrivel up in dry conditions. However, some mosses have an amazing capacity to recover quickly when wetted after a long period of drought. A few species grow in salt marshes or among the lichens at the top of rocky shores; on sheltered coasts, where there is little salt spray, they may live only just above the high tide level. Sand-dune mosses grow rapidly to keep pace with accumulating sand, and blown fragments of moss can colonize new areas of dunes. Many more moss species grow on sea cliffs and in damp gullies away from the intertidal zone. SYNTRICHIA RURALIFORMIS

This moss grows in coastal sand dunes. Its leaves curl up when dry (left of picture) but unfurl a few minutes after wetting (on right).

CLASS BRYOPSIDA

CLASS BRYOPSIDA

CLASS BRYOPSIDA

Golden Dune Moss

Salt Marsh Moss

Seaside Moss

Syntrichia ruraliformis

Hennediella heimii

Schistidium maritimum

SIZE

1/ –11/ 2 2

in (1–4 cm)

SIZE

Yellow-green to orange-brown cushions and carpets

FORM

HABITAT

1/ 8

FORM

in (3 mm)

Single green

plants Salt marshes, other coastal areas

HABITAT

Mobile dunes

SIZE

1 in (2 cm)

Dark blackish green, compact cushions

FORM

Hard, acidic rocks, salt marshes

HABITAT

DISTRIBUTION

Patchy distribution on temperate and cool waters worldwide

DISTRIBUTION Western and eastern coasts of North America, coasts of western Europe

This is one of the first mosses to colonize mobile dunes. It often forms extensive colonies that cover many square yards of sand, giving the sand a golden tinge. Its leaves are covered by hundreds of small papillae that enable swift absorption of water. The leaves gradually taper into long white hair points. This moss is able to establish new plants from fragments dispersed by the wind.

This tiny moss is a halophyte, meaning it is adapted to growing in highly saline conditions. It is rarely found growing inland. One of the few mosses that may be regularly found in salt marshes, it grows on patches of bare ground between the other vegetation in the upper parts of the salt marsh. It also grows in various other coastal habitats, including the banks of creeks, behind sea walls, and on footpaths. Although small, the plants may be abundant and may appear conspicuous from a distance, due to their prolific number of stout, dark, rusty-brown capsules, which are borne on short stalks less than 1/2 in (1 cm) tall. These have a little cap with a long point, which lifts to allow spores to escape, but remains attached to the capsule by a central stalk. The Salt marsh Moss has a wide distribution in colder climates.

This moss grows as small, dark green cushions on hard, acidic rocks, with seashore lichens, just above high-tide mark. It also occurs in salt marshes. It is often soaked by salt spray and occasionally covered by

CLASS BRYOPSIDA

Southern Beach Moss Muelleriella crassifolia SIZE

1–5 in (2–13 cm) FORM

Black cushions and mats HABITAT

Rocks DISTRIBUTION Southern tip of South America, islands in the Southern Ocean

This moss is the southern version of seaside moss (see above), growing on coastal rocks in the usually lichen-dominated splash zone, where it is often inundated by the sea in stormy weather. It grows in southern Chile and on subantarctic islands, where it can become dominant. On Heard Island, for example, a salt spray community of plants found on exposed coastal lava rock, at elevations of less than 16 ft (5 m), is dominated by southern beach moss, which has also colonized derelict buildings.

OCEAN LIFE

DISTRIBUTION Eastern Pacific, northwestern Atlantic, Mediterranean

the highest tides. Seaside moss appears to be a true halophyte, functioning normally even after immersion in sea water for a few days, and growing only in saline conditions; in Britain, it is found no farther than 1,300 ft (400 m) from the sea. Its leaves curl when dry. In winter, it produces small brown capsules on short stalks.

250

PLANT LIFE

Flowering Plants PLANTS CONQUERED LAND,

and then land-based flowering plants KINGDOM Plantae grew to be among the most DIVISION Trachaeophyta abundant and diverse life-forms CLASS Angiospermae on Earth. However, relatively SPECIES 260,000 few have adapted to the poor soil, salt spray, and drying wind of coastal dunes and cliffs. These few include some fascinating plants found nowhere else. Few flowering plants have returned to the sea: salt-marsh plants and mangroves get wet at high tide, but only the seagrasses live fully submerged. DOMAIN Eucarya

Anatomy

OCEAN LIFE

Flowering plants, technically called angiosperms, uniquely possess fruit and flowers, unlike mosses, seaweeds, and other algae. They are adapted to life in air, absorbing fresh water through their roots. If they take salt water into their vascular system, water from their own cell sap is attracted to the more concentrated salts and sucked out by osmosis. This is fatal to cells, but mangroves cope by excreting the salt, while succulents partition it within their cells. Seagrasses have fully adapted by matching their cells’ salt concentration to that of seawater. Most seagrasses have a similar form, with thin, grasslike blades that allow easy exchange of nutrients and gases. Mangroves grow in mud that lacks oxygen by growing aerial roots to waterproof assist gas exchange in their underground roots. Many seed case angiosperm seeds are killed by seawater, but those of the coconut can stay viable at sea for long periods inside a waterproof case. Seagrasses are germinating water-pollinated, and to plant GERMINATING SEED increase the chances of a This coconut is a fruit—a defining pollen grain catching onto characteristic of flowering plants. The a female stigma, pollen is coconut has the marine adaptations of buoyancy and a waterproof case. released as a sticky string.

Seawater Plants Seagrasses are monocotyledons (the group of flowering plants with narrow, straplike leaves), but are not true grasses, and they do not share a single evolutionary origin. There are 59 species in 5 families, although the Ruppiaceae, living mainly in brackish water, is not always accepted as a seagrass family. Salt-marsh plants are mainly small and herbaceous, with early colonizers including the salt-excreting cord grass and small succulents, such as common glasswort. Further salt-tolerant flowering plants grow farther up the shore in established salt marshes, forming a dense, grassy turf. Salt marshes (see p.124) form in cooler climates, and are replaced in tropical seas by mangroves—trees with characteristic aerial roots. There are 16 families and 54 species of mangroves. Like seagrasses, they do not have a single origin, so the mangrove habit evolved separately, several times. EELGRASS MANGROVES SUBMERGED

When the tide is in, mangroves form a mini-jungle of arching roots where small fish hide.

Seagrasses, such as this eelgrass in a Scottish sea loch, can be found from the cold waters of Alaska to tropical seas.

Coastal plants A greater variety of flowering plants can grow above the high-water mark. Salt-tolerant grasses are important constituents of the upper parts of salt marshes, and at the seaward edge of sand-dune systems, grasses are often the first to stabilize the shifting sand. In sand and sheltered gravel at the top of the shore, a few deep-rooted plants grow. A much wider variety of flowers and a few mosses colonize sand dunes and slacks just inland from the coast. Here they are subjected to salt spray but never inundated by tides. Nitrogen fixers thrive in these poor, sandy soils. In warmer climates, annuals bloom like desert flowers after seasonal rains. On cliff-tops, plants may be fertilized by sea-bird guano, stimulating lush growth.

DUNE-SLACK FLORA COASTAL FLOWERS

The beautiful pink flower heads of sea pink transform rocky seashores and salt marshes in late spring. The sea pink’s compact cushions resist wind and cold.

Here, in dune slacks behind a beach in the Canary Islands, annual plants bloom for a short period after rain. They flower and produce seeds quickly before drying up in the summer sun.

FLOWERING PLANTS ORDER NAJADALES

ORDER HYDROCHARITALES

Marram grass is a tall, spiky grass that plays a key role in binding coastal sand and building sand dunes. Its underground stems (rhizomes) spread

through loose sand, and upright shoots develop regularly along their length. When the tangle of stems and leaves impede onshore breezes, sand carried in the wind is deposited. Progressively, the sand builds up, the stems grow up through the sand, and a sand dune is formed. In dry weather, the leaves curl into a tube. The underside of the leaf then forms the outer surface and its waxy coating helps to reduce water loss from the plant. Marram grass is widely planted to stabilize eroded dunes, and has been introduced for this purpose to North America (where it is known as European beach grass), Chile, South Africa, Australia, and New Zealand.

thick, waxy skin. It is able to prevent the salt absorbed through its roots from doing any damage by locking it away in vacuoles (small cavities) within its cells. The plant stores water inside its succulent stems, hence its cactuslike shape. For centuries, glasswort was gathered and burnt to

produce an ash rich in soda (impure sodium carbonate). The ash was then baked and fused with sand to make crude glass—hence its common name. Glasswort can also be eaten boiled or pickled in vinegar. It has a mild, salty flavor, and is also known as poor man’s asparagus.

ORDER POALES

Neptune Grass

Paddle Weed

Marram Grass

Posidonia oceanica

Halophilia ovalis

Ammophila arenaria

DISTRIBUTION

TYPE

TYPE

TYPE

Perennial

Perennial

Perennial

HEIGHT

HEIGHT

HEIGHT

12 in (30 cm)

21/2 in (6 cm)

11/2–4ft (0.5–1.2 m)

HABITAT

HABITAT

HABITAT

Rocks and sand

Sand

Coastal sand dunes

Mediterranean

Coasts of Florida, USA, East Africa, Southeast Asia, Australia, and Pacific islands

DISTRIBUTION

Neptune grass (also known as Mediterranean tapeweed) forms meadows from shallow water to a depth of 150 ft (45 m) in the clearest waters. It grows on both rock and sand, has a tough, fibrous base, and persistent rhizomes (stems) that grow both horizontally and vertically. These build up into a structure known as “matte,” which can be several meters high and thousands of years old. Around the island of Ischia, Italy, more than 800 species have been associated with Neptune grass beds.

DISTRIBUTION Western Europe and Mediterranean (natural occurrence); introduced elsewhere

251

Members of the genus Halophila look quite unlike other seagrasses, having small, oval leaves that are borne on a thin leaf stalk. As its scientific name indicates, paddle weed is particularly tolerant of high salinities (halophila means “salt-loving”). Pollination takes place underwater, and the tiny, oval pollen grains are released in chains, which assemble into rafts like floating feathers. This is thought to increase the chances of pollination of a female flower. Despite its small size, paddle weed is an important food for the dugong (see p.419). An adult can eat more than 88 lb (40 kg) of it a day.

ORDER CARYOPHYLLALES

Common Glasswort Salicornia europaea Annual

4–12 in (10–30 cm)

HEIGHT

Coastal mudflats and salt marshes

HABITAT

DISTRIBUTION Coasts of western and eastern North America, western Europe, and Mediterranean

OCEAN LIFE

TYPE

Glasswort, also known as marsh samphire, is an early colonizer of the lower levels of salt marshes and mudflats, where plants are inundated twice a day by the tide. It is a small, cactuslike plant with bright green stems that later turn red. The tiny flowers and scale-like leaves are sunk into depressions in the fleshy stem. Glasswort is protected externally from salt water and moisture loss by a

252

PLANT LIFE ORDER PLUMBAGINALES

Common Sea Lavender Limonium vulgare

in Wales, while others are only found in parts of Sicily or Corsica.Varieties of sea lavender, often called statice, are grown commercially as “everlasting” flowers. The colored, papery “flowers” are actually what remains after the true flowers have fallen.

ORDER PAPAVERALES

Yellow Horned-poppy Glaucium flavum

Perennial

Biennial or perennial

HEIGHT

HEIGHT

TYPE

TYPE

20–36 in (50–90 cm)

8–20 in (20–50 cm)

HABITAT Shingle, sometimes sand

HABITAT

Muddy salt marshes DISTRIBUTION Coasts of western Europe, Mediterranean, Black Sea, and Red Sea

DISTRIBUTION

Coasts of western Europe, Mediterranean, and Black Sea

This showy plant, which flowers in late summer, often forms dense colonies in salt marshes, particularly along the sides of muddy creeks. Several closely related species of sea lavender are highly localized in their distribution. For example, two species are confined to two rocky peninsulas

Also known as yellowhorn poppy, this plant has leaves covered in a waxy coating to protect it from salt spray and reduce water loss. Its taproot penetrates deep into shingle in search of water beneath. It blooms through most of the summer, producing flowers that are up to 31/2 in (9 cm) across.

ORDER MYRTALES

ORDER POLEMONIALES

Beach Morning-glory

Pacific Stilt-mangrove

Ipomoea imperati

Rhizophora stylosa TYPE

Perennial

LENGTH

HABIT

Woody perennial

Commonly 5–8 m (16–26 ft), but can be up to 40m (130 ft)

Up to 16 ft

HEIGHT

(5 m) Coastal beaches and grasslands

HABITAT

HABITAT

Intertidal

mudflats DISTRIBUTION Widespread on many coasts and islands with tropical or warm temperate climates

This pioneer plant helps to stabilize coastal sands, creating a habitat into which other species move. It can endure low nutrient levels, high soil temperatures, abrasion and burial by blown sand, and occasional frosts, but not hurricanes, according to studies in Texas. It also grows occasionally on disturbed ground inland. Beach morning-glory is recorded on six continents and many isolated islands.

PROFILE CAPPARALES

Scurvy-grass Cochlearia officinalis HABIT Biennial or perennial HEIGHT 4–16 in (10–40 cm)

Coastal rocks and salt marshes

HABITAT

OCEAN LIFE

DISTRIBUTION Coasts of northern Europe and Asia and northern North America

The thick, fleshy leaves of this coastal plant help it to store water in an environment where fresh water soon drains away (scurvy-grass plants found on mountains have thinner leaves and may belong to a different species). Scurvy-grass leaves are rich in vitamin C. They were once eaten, or pulped and drunk, to prevent scurvy—a disease caused by vitamin C deficiency to which sailors were prone (“grass” is Old English for any green plant).

Coasts of northern Australia, Southeast Asia, and South Pacific islands

DISTRIBUTION

The aerial roots of Pacific stiltmangroves arch down from the main trunk, with secondary roots coming off the primary ones before they reach the ground to form a tangle of roots growing in all directions. When the tide is in, these form a sheltered refuge for many small fish. This species of mangrove can tolerate a wide range of soils, but thrives best in the fine, muddy sediments of river estuaries. Its roots absorb water selectively, so much of the damaging salt is not taken up, but it still has to excrete some salt through the leaves.

FLOWERING PLANTS ORDER CARYOPHYLLALES

Grand Devil’s-claw Pisonia grandis TYPE

Woody perennial

46–98 ft (14–30 m)

HEIGHT

Coastal and island forests

HABITAT

DISTRIBUTION Coasts and islands in Indian Ocean, Southeast Asia, and South Pacific

ORDER ARECALES

The grand devil’s-claw is typically found on small tropical islands and its distribution is associated with sea bird colonies. It can grow as tall as 98 ft (30 m), the trunk can be up to 61/2 ft (2 m) in diameter, and it is often the dominant tree in coastal forests that are undisturbed by humans. The trees provide nesting and roosting sites for many species of sea bird, whose guano is an important fertilizer on isolated islands. The branches break easily, and can root in the ground.

BIRD-KILLING TREE The seeds of grand devil’s-claw are produced in clusters of 50–200 and exude a resin that makes them extremely sticky. They attach to the feathers of sea birds and may subsequently be flown to remote islands. This is an effective means of dispersal, but the seeds are so sticky that small birds often become completely entangled and die.

253

ORDER CASUARINALES

Casuarina Casuarina equisetifolia TYPE

Woody perennial

66–98 ft (20–30 m) HEIGHT

Coastal and island forests

HABITAT

DISTRIBUTION Southeast Asia, eastern Australia, and islands in southeast Pacific

Casuarina has many common names, including Beach she-oak, beefwood, ironwood, and Australian pine. It is typically found at sea level, but also grows inland to 2,600 ft (800 m). Casuarina is fast-growing, reaching a height of 65 ft (20 m) in 12 years. It is drought-tolerant, and can grow in poor soils because it can fix nitrogen in nodules on its roots. Its wood is very hard and is used as a building material and as firewood. The bark is widely used in traditional medicines.

COCONUT TREE

Coconut Palm Cocos nucifera HABIT

Woody perennial

The coconut palm can live as long as 100 years, a mature tree producing 50–80 coconuts a year. The trunk is ringed with annual scars left by fallen leafbases.

66–72 ft (20–22 m)

HEIGHT

Coastal rocky, sandy, and, coralline soils

HABITAT

DISTRIBUTION

Tropical and subtropical coasts

worldwide

The coconut palm was once the mainstay of life on Pacific islands. It provided food, drink, fuel, medicine, timber, mats, domestic utensils, and thatching for roofs. It remains an important subsistence crop on many Pacific islands today. Its original habitat was sandy coasts around the Indo-Malayan region, but it now is found over a much wider area, assisted by its natural dispersal mechanism, and deliberate planting by humans. The fibrous husk of the coconut fruit is a flotation aid that enables the seeds to be carried vast distances by ocean waves and currents. The coconut palm cannot develop viable fruits outside of the tropics and subtropics. COCONUT FRUIT

The fruit of the Coconut Palm weighs 2¼–4½ lb (1–2 kg). It contains one seed, which is rich in food reserves and is part solid (flesh) and part liquid (coconut milk).

fibrous husk

OCEAN LIFE

edible flesh

254

FUNGI

Fungi FUNGI FORM A GREAT KINGDOM OF SINGLE-CELLED

and filamentous life-forms, including yeasts and moulds. Some organise their filaments KINGDOM Fungi into complex fruiting structures, such as mushrooms. Truly marine PHYLA 5 fungi are rare, but a few fungus-like organisms survive within a slime SPECIES 46,574 covering, avoiding contact with salt water. Fungi are abundant on shorelines, but only in close association with certain algae. Alga and fungus grow in partnership in a kind of symbiotic, compound organism called a lichen. Lichens proliferate in the hostile, wave-splashed zone of bare rock just above high tide. DOMAIN Eucarya

Anatomy A lichen’s body (thallus) is composed mainly of fungal filaments called hyphae. The cells of the fungus’s algal partner are restricted to a thin layer below the surface, where they cannot dry out. Lichens grow in one of four ways: bushy (fruticose); leaf-like (foliose); tightly clustered (squamulose); or lying flat (crustose). Marine fungus-like organisms, such as slime nets (labyrinthulids) and thraustochytrids, are microscopic, usually transparent, and encased in a network of slimy threads. The cells move up and down within the threads and react positively towards food. They are increasingly recognized as protists, however, rather than fungi. LICHEN COMPOSITION

This false-colour micrograph of a lichen (below) shows the smooth surface of the thallus, to the left, and fungal hyphae, to the right.

ENCASED IN SLIME

This thraustochytrid (above) is a fungus-like organism that lives as a parasite within certain bivalves. Its slime net forms a complete cover.

OCEAN LIFE

Habitats Most lichens require alternating dry and wet periods, but marine lichens can withstand continuous drought or dampness. On most rocky shores, yellow and grey lichens dominate surfaces splashed by waves at high tide (the splash zone). They endure both the drying Sun and wind, and the salt spray of the sea. Below, in the tidal zone, the brightly coloured lichens give way to black encrusting lichen, such as Verrucaria maura, which covers the bedrock and any large, stable boulders. Verrucaria serpuloides lives yet further down the shore and is the only lichen to survive permanent immersion in sea water. Slime nets can live in the sea because they are protected from the dehydrating effects of salt water by slime, or because they live as parasites within seagrasses, green algae, or clams. BELOW THE SPLASH ZONE

Some lichens, such as this crustose black Verrucaria, live below the splash zone, and may be surrounded by seaweeds.

LICHEN ENCRUSTATION

Fungi thrive on the coast if they grow in association with algae, in an intimate symbiosis called lichen. Here, encrusting and foliose lichens cover sandstone cliffs in the Shetland Isles, Scotland.

255 PHYLUM ASCOMYCOTA

Sea Ivory

PHYLUM ASCOMYCOTA

Yellow Splash Lichen

Ramalina siliquosa

Xanthoria parietina

LENGTH (BRANCHES)

WIDTH

1–4 in (2–10 cm)

Up to 4 in (10 cm) HABITAT

HABITAT

Splash zone; favors surfaces high in nitrogenous compounds

Hard siliceous rocks above the splash zone DISTRIBUTION Northeast and southwest Atlantic, coasts of Japan and New Zealand

DISTRIBUTION

Temperate Atlantic, Gulf of Mexico, Indian and Pacific oceans

Nutrient-poor siliceous rocks are the favorite habitat of gray lichens, such as sea ivory. This lichen is usually gray-green in color, with a brittle, bushlike (fruticose) structure and disk-shaped fruiting bodies, called apothecia, at its branch tips. Sea ivory cannot withstand being trampled or extensively grazed, and so it grows best on vertical rock faces, to which it sticks by a single basal attachment.

On most rocky shores, different species of lichen have a marked vertical territory related to their tolerance of salt exposure. The yellow splash lichen is found in the splash zone and forms a bright orange band across the shore, with gray lichens above it and black lichens below. It has a leaflike (foliose) form, with slow-growing, leafy lobes held more or less parallel to the rock on which it lives. Usually bright orange in color, it tends to become greener if in shade. Lichens are widely used to monitor air pollution because they simply disappear when conditions deteriorate. The yellow splash lichen is particularly sensitive to sulfur dioxide, a by-product of industrial processes and of burning fossil fuels.

PHYLUM ASCOMYCOTA

Black Tar Lichen PHYLUM ASCOMYCOTA

Verrucaria maura THICKNESS

Black Shields

1/32

in (1 mm)

HABITAT

Tephromela atra

Intertidal WIDTH

Up to 4 in (10 cm) HABITAT

DISTRIBUTION

In and above the splash zone

Ocean, Japan

Temperate and polar coasts, Indian

This smooth, black, crustose lichen covers large areas of bedrock or stable boulders in a thin layer, making them appear as though they have been covered with dull black paint. Many types of lichen accumulate heavy metals, and the black tar lichen is no exception, having been found to have levels of iron that are about 2.5 million times more concentrated than the surrounding seawater. That may be an adaptation to deter grazers, such as gastropods, from eating it.

PHYLUM ASCOMYCOTA

Gray Lichen Pyrenocollema halodytes SIZE

Not recorded HABITAT

Upper shore on rocks and on shells of some sedentary invertebrates DISTRIBUTION

Temperate northeast and southwest

Atlantic

Seen on hard, calcareous rocks, where it forms small, black-brown patches, gray lichen is unusual in being an association of three organisms— a fungus, a cyanobacteria, and an alga. The fungus anchors the lichen to the rock; the cyanobacteria and the alga contain chlorophyll and make food by photosynthesis. The cyanobacteria can also utilize nitrogen, a process that uses a lot of energy, and this comes from the sugar made during photosynthesis.

Polar coasts, coast of California, US, Gulf of Mexico, Mediterranean, Indian Ocean DISTRIBUTION

Crustose lichens such as black shields, which form a crust over the rock, attach themselves so firmly using fungal filaments that they cannot be easily removed from it. Over time, these anchoring filaments break down the rock as they alternately shrink when dry and swell when moist. Black shields is a thick, gray lichen with a rough, often cracked, surface from which project a number of characteristic black fruiting bodies. PHYLUM ASCOMYCOTA

Black Tufted Lichen Lichina pygmaea To 1/2 in (1.5 cm) HABITAT

Lower littoral fringe to middle shore, regularly covered by the tide Northeast Atlantic from Norway to northwest Africa

DISTRIBUTION

OCEAN LIFE

WIDTH (LOBES)

Typically found on exposed sunny rock faces, this lichen looks rather like a seaweed, being fruticose (bushlike) in form with branching, brownish black, flattened lobes. Its fruiting bodies form in small swellings at its branch tips. It is often seen growing in association with barnacles but does not tolerate algal (seaweed) growth. Its compact growth and rigid branches provide a refuge for several mollusks, particularly Lasaea rubra, a small, pink-shelled gastropod. All Lichina species are limited to coastal habitats.

256

ANIMAL LIFE

Animal Life ANIMAL LIFE FIRST APPEARED IN THE OCEAN

over one billion years ago. It has since diversified into a vast KINGDOM Animalia array of different organisms. The range of scale among PHYLA About 30 marine animals is immense: the smallest invertebrates SPECIES Over 1.5 million are over half a million times smaller than the largest whales. Despite this huge disparity, animals all share two key features. First, they are heterotrophs, meaning they obtain energy from food. Second, they are multicellular, which distinguishes them from single-celled life forms. DOMAIN Eucarya

Marine Animal Diversity

CHANGING SHAPE

Most invertebrates change shape as they develop. Feather stars start as drifting larvae, which eventually attach themselves to corals or rock before changing into swimming adults.

Animals are classified into 30 or more major groups (phyla), all of which include at least some marine animals. Twenty-nine of these phyla are composed of animals without backbones (invertebrates), each phylum representing a completely different body plan. Only one phylum, the chordates, contains animals with backbones (vertebrates). In salt water, vertebrates include fish, reptiles, birds, and mammals— animals that are often described as the dominant forms of ocean life. However, in terms of abundance and diversity, invertebrates have a stronger claim to this title. Invertebrates exist in all ocean VERTEBRATE habitats and outnumber marine Active predators, such vertebrates by a million to one. as this barracuda, need sharp senses and rapid They include an array of fixed reactions to catch prey. (sessile) animals, such as corals and Unlike invertebrates, they sponges. They also form most of the have fast-acting nerves zooplankton, a drifting community and well-developed of tiny animals and animal-larvae. brains.

INVERTEBRATE

This yellow tube sponge, from the sea off Belize, is a typical sessile invertebrate. Instead of moving to find food, it filters out particles of food by pumping water through its pores.

Support and Buoyancy On land, most animals have hard skeletons to counteract gravity’s pull. Life is different in the sea, because water is denser than air. It buoys up soft-bodied animals, such as jellyfish, enabling them to grow large. They use internal pressure to keep their shape, the same principle that works in balloons. Animals with hard body parts, such as fish and mollusks, are often denser than water, and would naturally sink. To combat this, many have a buoyancy device. Bony BUBBLE RAFT The violet sea snail fishes have an adjustable gas-filled swim bladder, stays afloat by producing while squid have an internal float made of chalky bubbles of mucus. material, containing many gas-filled spaces. Some The mucus slowly surface dwellers, such as the violet sea snail, have hardens, forming a permanent raft. gas-filled floats that prevent them from sinking.

OCEAN LIFE

Groups and Individuals Among marine animals, there is a social spectrum from species that live on their own to those that form permanent groups. The whale shark is a typical solitary species, spending its entire life on its own apart from when it breeds. It can do this because its huge size means it has few natural predators. Smaller fish often form shoals, which reduce each fish’s chances of being singled out for attack. Many invertebrates, from corals to tunicates, live in permanent groups, known as colonies. In most coral colonies, the individual animals, or polyps, are anatomically identical and function as independent SAFETY IN units, even though they are joined. NUMBERS Crowded together Other animal colonies, such as the in a ball, gregarious Portuguese man-of-war, are made striped catfish of individuals with distinct forms. (right) make a Each form carries out a different confusing target for predators. task, like parts of a single animal.

COLONY ON THE MOVE

LONE GIANT

A diver films a pyrosome colony in the sea off Florida. It consists of thousands of tiny soft-bodied animals called tunicates, joined together to form a tube.

The whale shark (below) is a solitary species with a pantropical range. It only congregates in particular regions during the breeding season.

ANIMAL LIFE

257

SINGLE PARENT

Reproduction Animals reproduce in two ways. In asexual reproduction, which occurs in many marine animals from flatworms to sea anemones, a single parent divides in two, or grows (buds off) parts that become independent. In sexual reproduction, the eggs of one parent are fertilized by the sperm of another. Sessile animals, such as corals and clams, usually breed sexually by shedding their eggs and sperm into the water, leaving them to meet by chance. In some fish, all mammals, and birds, fertilization is internal, which means that the two parents have to mate. Marine animals vary greatly in reproductive potential. Most whales have a single calf each time they breed, but an ocean sunfish can produce over 300 million eggs a year. COURTSHIP

This sea anemone is budding off young that will eventually take up life on their own. Asexual reproduction is quick and simple, but it does not produce genetic variation, making it more difficult for a species to adapt to change.

SEA SYMPHONY

A wrasse feeds among coral in the Red Sea. Coral reefs contain the greatest diversity of animal life in the oceans, and are one of the few habitats that are actually created by animals.

Two waved albatrosses display to each other in the Galápagos Islands. Complex courtship rituals like this ensure that each parent finds a partner of the right species and the right sex, and they cement the bond once breeding begins.

OCEAN LIFE

258

ANIMAL LIFE

Sponges

osculum

Anatomy THIS ABUNDANT AND

diverse group DOMAIN Eucarya of often colorful invertebrates lives KINGDOM Animalia permanently attached to the sea floor. PHYLUM Porifera Naturalists once thought they were CLASSES 4 plants, but they are now known to SPECIES About 8,700 be very simple animals with no close relatives. Sponges live by drawing water into their bodies through tiny holes called pores, filtering it for food and oxygen and pushing it out again. Many species are found on coral reefs or rocks, and a few live in fresh water.

The body plan of a sponge is based on a system of water canals lined with special cells known as collar cells. Collar cells are unique to sponges. They draw water into the sponge through pores, by each beating a long, whiplike flagellum. A ring of tiny tentacles around the base of the flagellum traps food particles, and the water and waste material then flows out of the sponge through larger openings. Rigidity is provided by a skeleton made up of tiny splinters (spicules) of silicon dioxide or calcium carbonate scattered throughout the body.

Habitats Most sponges need a hard surface for attachment, but some can live in soft sediment; a few species are able to bore into rocks and shells. Sponges are common on rocky reefs, shipwrecks, and coral reefs in a wide range of temperatures and depths. The largest populations occur where there are strong tidal currents, which bring extra food. Animals such as crabs and worms sometimes live inside sponges, but little manages to settle and grow on their surface. This is because sponges produce chemicals to discourage predators.

central cavity collar cell flagellum spicule

pore

BODY SECTION

A sponge has specialized cells, but no organs. Water enters the sponge through hollow pore cells and exits via larger openings called osculae.

CHANGING SHAPE

Many sponges grow different shapes in different habitats. This sponge develops fingers in strong currents (above), but has an encrusting form (right) when it grows in wave-exposed sites.

VARIETY OF FORM

Sponges come in many forms, including tubes, spheres, and threadlike shapes. Pictured are a brown tube sponge and an irregular deep red sponge.

CLASS DEMOSPONGIAE

Barrel Sponge Xestospongia testudinaria HEIGHT

Up to 6 ft (2 m) DEPTH

6–165 ft (2–50 m) HABITAT

Coral reefs DISTRIBUTION

Pacific

CLASS HEXACTINELLIDA

OCEAN LIFE

Reef-forming Sponge Heterochone calyx HEIGHT Up to 5 ft (1.5 m) DEPTH 300–800 ft (100–250 m) HABITAT

Deep hard

seabed DISTRIBUTION

Deep cold waters of north Pacific

The reef-forming sponge not only looks like a delicate glass vase, but its skeleton spicules are made from the same material as glass, silica. Each spicule has six rays, hence the scientific name of its class, Hexactinellida. Many glass sponges grow very large—off Canada’s British Columbian coast, the reef-forming sponge forms huge mounds nearly 65 ft (20 m) high spread over several miles. Other members of their class also contribute to these reefs, which may have started forming nearly 9,000 years ago. Like coral reefs, sponge reefs provide a home for many other animals.

Tropical waters of western

These gigantic sponges grow large enough to fit a person inside. Their hard surface is deeply ridged, but their rim is thin and delicate. The barrel sponge belongs to the Demospongiae, the largest class of sponges, containing about 95 percent of sponge species. The skeleton of sponges in this class is made from both scattered spicules of silica and organic collagen called spongin. An almost identical barrel sponge, Xestospongia muta, occurs in the Caribbean.

259 CLASS HOMOSCLEROMORPHA

Flesh Sponge Oscarella lobularis About 0.3 in

HEIGHT

(1 cm) HABITAT

Sublittoral rock

DISTRIBUTION

CLASS DEMOSPONGIAE

Breadcrumb Sponge Halichondria panicea To more than 12 in (30 cm)

WIDTH

Shore to sublittoral zone

DEPTH

HABITAT

Hard surfaces

DISTRIBUTION Temperate coastal waters of northeastern Atlantic and Mediterranean

The appearance of this soft encrusting sponge varies from thin sheets to thick crusts and large lumps. On waveexposed shores, it usually grows under ledges as a thin, green crust, its osculae opening at the tops of small mounds. Its green color is produced by photosynthetic pigments in symbiotic algae in the sponge’s tissues. In deeper, shaded waters, the sponge is usually a creamy yellow. In waters with strong currents, this sponge may cover large rocky areas and kelp stems.

Mediterranean and south to Senegal

The blue color of this species is unusual among sponges but this species can also be green, violet, or brown. It grows as irregular lobules that look and feel smooth and soft because it has no spicules. It doesn’t have many other skeletal fibers either and collapses when out of water. This genus of sponges, along with six others, have recently been separated out from the demosponges and placed in their own class. A similar yellow sponge that occurs around the UK is called by the same name but the two forms are thought to be different species.

CLASS DEMOSPONGIAE

Tube Sponge Haliclona fascigera HEIGHT

Up to 3 ft (1 m) DEPTH

Below 33 ft (10 m) HABITAT

Coral reefs DISTRIBUTION Tropical reef waters of western Pacific; likely to be more widespread than shown

The elegant, tubular branches of this beautiful sponge are easily torn, and so it occurs only on deeper reef slopes, where wave action is minimal.

CLASS DEMOSPONGIAE

CLASS DEMOSPONGIAE

Mediterranean Bath Sponge

Coralline Sponge Vaceletia ospreyensis

Spongia officinalis

SIZE

Not recorded

WIDTH

DEPTH

Up to 14 in (35 cm)

At least 65 ft (20 m)

DEPTH

HABITAT

3–165 ft (1–50 m)

Dark reef caves

HABITAT

DISTRIBUTION Not fully known, but includes tropical waters of western Pacific

Rocks DISTRIBUTION

It sometimes grows as a single tube, but it is more often seen as bunches of tubes joined at the base. The tips of the tubes are translucent and slightly rolled in. The color of this sponge is usually pinkish violet, although some specimens are pinkish blue. When this sponge releases sperm, it resembles smoking chimneys. The taxonomic status of this species and its relationship to other species in the same family has not been fully determined, and it is listed under various names in different sources. Such uncertainties are not unusual in the study of sponges and mean that the exact distribution of this and many other species is yet to be established.

Mediterranean, especially the

eastern part

CLASS CALCAREA

Lemon Sponge Leucetta chagosensis WIDTH Up to 8 in (20 cm) DEPTH

Shallow

Steep coral reef and rock slopes HABITAT

DISTRIBUTION

Tropical reef waters of western

Pacific

The lemon sponge is a beautiful, bright yellow color and is easy to spot underwater. It grows in the form of sacs, which may have an irregular,

OCEAN LIFE

The Mediterranean bath sponge, as its name suggests, is collected and processed for use as a bath sponge. It grows as rounded cushions and mounds, and is usually dull gray to black outside but yellowish white inside. It can be used as a sponge because it has no sharp skeletal spicules, just a network of tough fibers made from an elastic material called spongin. Huge numbers were once harvested, but today they are rare.

lobed shape. Each sac has a large opening—the osculum—through which used water flows out of the sponge. Through the osculum, entrances to the water-intake channels that run throughout the sponge can be seen. The lemon sponge belongs to a small class of sponges in which the mineral skeleton is composed entirely of calcium carbonate spicules, most of which have three or four rays. The densely packed spicules give the sponge a solid texture. Like all sponges, this sponge is hermaphroditic. It incubates its eggs inside and releases them as live larvae through the osculum. Each larva is a hollow ball of cells with flagellae for swimming.

Vaceletia ospreyensis is a living member of the coralline sponges group, most of which are known only from fossils. Coralline sponges have a massive skeleton made of calcium carbonate, as well as silica spicules and organic fibers. They were the dominant reef-building organisms before the stony corals of modern reefs evolved. Once given a separate class (the Sclerospongiae), they are now accepted as part of the Demospongiae.

260

ANIMAL LIFE

Cnidarians

HUMAN IMPACT

CORAL TRINKETS

THIS ANCIENT GROUP OF AQUATIC ANIMALS

emerged in Precambrian times, about 600 million years ago. It includes KINGDOM Animalia reef-building corals, anemones, jellyfish, and hydroids, most PHYLUM Cnidaria of which are marine. Cnidarians have a radially symmetrical CLASSES 5 body shaped like a simple sac, with stinging tentacles around a SPECIES 10,886 single opening that serves as both mouth and anus. There are two body forms: the polyp form, typified by sea anemones, which is fixed to a solid surface and has an upward-facing mouth and tentacles; and the medusa, shown by adult jellyfish, which can swim and has a downward-facing mouth and tentacles. DOMAIN Eucarya

Anatomy Corals and anemones exist only as polyps, whereas other cnidarians can be either polyps or medusae at different stages of their life cycle. The body wall of both polyps and medusae consists of two types of tissue. On the outside is the epidermis, which acts like a skin to protect the animal. The inner tissue layer, lining the body cavity, is the gastrodermis, which carries out digestion and produces reproductive cells. Separating and connecting these two layers is a jellylike substance called the mesoglea. The tentacles have stinging cells called cnidocytes, which are unique to this phylum and give it its name. A simple nervous system responds to touch, chemicals, and temperature.

TENTACLE ARRANGEMENT

The number of tentacles on coral polyps varies from one group to another. The polyps of all soft corals (above) have eight tentacles, hence their alternative name of octocorals. Hexacorals (right) have tentacles arranged in multiples of six. POLYP tentacle

POLYP AND MEDUSA

Polyps are essentially cnidocyte a tube, closed at one epidermis end, that attaches to a mesoglea hard surface by a basal gastrodermis disk. They live singly or in colonies. Medusae budding are bell-shaped and juvenile usually have a thicker gut mesoglea; some also have a shelf of muscle basal for locomotion. disk

epidermis

mesoglea gastrodermis

gut mouth shelf of muscle (velum)

tentacle MEDUSA

epidermal cell coiled thread

BEFORE nematocyst DISCHARGE barbs

uncoiled hollow thread

AFTER DISCHARGE

STINGING CELLS

Each cnidocyte contains a bulblike structure, called a nematocyst, which houses a coiled, barbed thread. When triggered by touch or chemicals, the thread explodes outward and pierces the prey’s skin. The animal’s tentacles are then used to haul the victim in.

OCEAN LIFE

SCLERITES

Small slivers of calcium carbonate called sclerites are scattered through the tissues of soft corals and sea fans. Here, they are visible as white shards under the skin of this soft coral. BUILDING REEFS

Coral reefs are built by colonies of coral polyps that secrete a hard exoskeleton of calcium carbonate. As the tiny polyps divide and grow, the reef expands.

Many corals are harvested for sale as souvenirs, and the most valued species are being overcollected. Particularly desirable are certain soft corals, in which the calcareous supporting column is so strong and dense it can be carved and polished. They include the red or precious coral, Corallium rubrum (below). As yet, there are no international regulations controlling trade in this species, although some countries restrict its collection. Black corals (order Antipatharia) also have strong skeletons that can be carved.

CNIDARIANS

Locomotion

Reproduction

The most mobile cnidarians are free-living jellyfish and medusae, which mainly drift in water currents but also swim actively using a form of jet propulsion. Most colonial cnidarians, such as corals and sea fans, cannot move from place to place. However, they can expand and contract their polyps to feed or avoid danger, and some sea pens can withdraw the whole colony below the surface of the sediment in which they live. Unattached mushroom corals may move JELLYFISH SWIMMING slowly, or even right themselves if A jellyfish swims by using muscles overturned. Anemones can creep slowly to contract its bell, forcing water out over the seabed on their muscular basal and pushing it along. The muscles then disk, and a few species swim if attacked. relax and the bell opens again.

Members of the class Anthozoa, such as corals and anemones, reproduce by asexual budding. A genetically identical copy of the adult grows on the polyp’s body wall. This budding juvenile drops off or stays attached to form a colony. Anthozoans also reproduce sexually, producing eggs and sperm within the polyps. Fertilized eggs develop into hairy, oval larvae (planulae), which either swim free or are brooded internally and then released. Hydrozoans have a two-stage life cycle. Their polyps release tiny free-swimming medusae into the water which, when mature, shed eggs and sperm. The resulting fertilized eggs develop into planulae that settle in a new area to grow into polyps. In contrast, the medusa form of jellyfish is usually much larger than the fixed polyp form and the polyps bud asexually.

261

BUDDING JELLYFISH POLYPS

bell relaxed and flattened, ready to propel forward

bell begins to contract and force water out

Jellyfish polyps are minuscule, and their sole function is to reproduce asexually by budding off baby jellyfish.

bell fully contracted, with little water remaining inside

Zooxanthellae The massive skeletons secreted by reef-building corals require energy for their construction. Corals cannot catch enough plankton in clear tropical waters to provide this energy. Instead, they rely on tiny, symbiotic single-celled algae, called zooxanthellae, living in their cells. These algae manufacture organic matter by photosynthesis, and make more food than they need, so the excess is used by the coral. The algae benefit from a safe place to live and obtain “fertilizer” from the coral by using its nitrogenous waste products. If stressed by disease or high temperatures, corals expel their zooxanthellae, in a process called coral bleaching, and may die of starvation.

ZOOXANTHELLAE

In this image of coral polyps, the green patches are zooxanthellae living in the corals’ tissues. The zooxanthellae give color to the otherwise colorless polyps.

CNIDARIAN CLASSIFICATION Cnidarians are divided into five classes and a large number of orders and families. This phylum used to be called the Coelenterata, a name still used by some authorities. Many species remain undescribed. BOX JELLYFISH Order Cubozoa

ANTHOZOANS Order Anthozoa

41 species

7,095 species

These jellyfish have a cube-shaped bell with four flattened sides and a domed top. There are four tentacles or clusters of tentacles, one at each corner. Most are virulent stingers.

These colonial or solitary polyps are diverse in shape and have no medusa phase. Octocorals (soft corals, sea fans, and sea pens) have polyps with eight feathery tentacles; hexacorals (including hard corals and anemones) have polyps with multiples of six simple tentacles; ceriantipatharians have polyps with unbranched tentacles.

HYDROIDS Order Hydrozoa 3,516 species

These colonial cnidarians mostly resemble plant growths attached to the sea bed. A few have hard skeletons and resemble corals, and some colonies float at the surface like jellyfish. Most species have a free-living medusa stage.

48 species

Less than an inch high, stalked jellyfish have a bell-shaped body with eight clusters of short, knobbed tentacles around the rim of the bell. They attach to seaweeds by a stalk that extends from the “top” of the bell.

186 species

These mostly free-swimming medusae are shaped like a bell or saucer with a fringe of stinging tentacles. The edges of the mouth, located on the underside, are drawn out to form trailing mouth tentacles or oral arms.

OCEAN LIFE

STALKED JELLYFISH Order Staurozoa

JELLYFISH Order Scyphozoa

262 CLASS HYDROZOA

Blue Buttons Porpita porpita DIAMETER 3/ in 4

(2 cm)

DEPTH

Surface HABITAT

Surface waters DISTRIBUTION

Worldwide in warm waters

At first sight, blue buttons could be mistaken for a small jellyfish or even a piece of blue plastic. In fact, it is a hydrozoan colony that is modified for a free-floating existence. Swarms of these unusual creatures can be seen drifting on the water’s surface or can sometimes be found washed up on the shore. The animal is kept afloat by a buoyant circular disk. Around the edge hang protective stinging polyps modified as knobbed tentacles. In the center underneath hangs a large feeding polyp that acts as the mouth for the whole colony. In between this and the tentacles are circlets of reproductive polyps. Unlike the Portuguese man-of-war (see p.214) to which it is related, blue buttons do not have a powerful sting.

CLASS HYDROZOA

Stinging Hydroid Aglaophenia cupressina Up to 16 in

HEIGHT

(40 cm) DEPTH 10–100 ft (3–30 m) HABITAT

around among the corals on a reef. Individual polyps are arranged along one side of the smallest branches and extend their stinging tentacles to catch small planktonic animals. The sting is not usually dangerous to humans, but it results in an itchy rash that can irritate for up to a week.

CLASS SCYPHOZOA

CLASS SCYPHOZOA

Deep-sea Jellyfish

Moon Jellyfish

Periphylla periphylla

Aurelia aurita

8–14 in (20–35 cm)

HEIGHT

DIAMETER

Up to 12 in (30 cm)

3,000–23,000 ft (900–7,000 m)

DEPTH

Coral reefs

HABITAT

DEPTH

Near surface

Open water

HABITAT

Open water DISTRIBUTION

While most hydroids are harmless to touch, the stinging hydroid has a powerful sting. The colonies look like clumps of feathers or ferns dotted

This jellyfish belongs to a group called coronate jellyfish, which are shaped like a ballet tutu. The upper part of the bell is a tall, stiff cone and the lower part a wider, soft, crown-shaped base with a scalloped edge. The 12 thin tentacles are often held in an upright position. The insides of the deep-sea jellyfish are a deep red color, and this may hide the bioluminescent light given out by its ingested prey. The jellyfish itself can squirt out a bioluminescent secretion that may help to confuse any predators. Unlike many jellyfish, the deep-sea jellyfish does not develop from a fixed bottom-living stage.

CLASS SCYPHOZOA

Stalked Jellyfish Haliclystus auricula HEIGHT

Up to 2 in (5 cm) DEPTH

0–50 ft (0–15 m)

HABITAT

On seaweed or

seagrass DISTRIBUTION

north Pacific

OCEAN LIFE

Deep water worldwide, except

Tropical reefs in Indian Ocean and southwestern Pacific DISTRIBUTION

Coastal waters of north Atlantic and

DISTRIBUTION

Worldwide; polar distribution unknown

Arctic Ocean

Most jellyfish drift and swim freely in the water, but stalked jellyfish spend their lives attached by a stalk to vegetation. The body of the jellyfish is shaped like a tiny funnel made up of eight equally spaced arms joined together by a membrane. Each arm ends in a cluster of tentacles on the funnel rim, and in some species there is an extra anchor-shaped tentacle between these. This animal cannot swim, but it can move by bending over on its stalk and turning “headover-heels,” using the anchor tentacles to fix itself temporarily to the sea bed as it flips over and then reattaches its adhesive disk. Stalked jellyfish can be found attached to seaweed or seagrass in the intertidal zone and shallow water, where they feed by catching prey, such as small shrimp and fish fry, with their tentacles and passing it to the mouth inside the funnel. Undigested remains are expelled from the mouth.

tentacle held upright

scalloped edge of bell

The moon jellyfish is possibly the most widespread of all jellyfish and can be found in almost every part of the ocean except for very cold waters. It exists mainly in coastal waters and is sometimes cast ashore in large numbers because it is not a strong swimmer and lives near the surface. The body is shaped like a saucer with a fringe of fine, short tentacles, which it uses to catch plankton. It can also trap plankton in sticky mucus on its bell and slide this down into its mouth on the underside. The gonads show through the translucent bell as four opaque horseshoe shapes.

CNIDARIANS

263

gonads

stinging tentacle

frilly mouth lobe

CLASS SCYPHOZOA

Mauve Stinger Pelagia noctiluca DIAMETER

Up to 5 in (13 cm) DEPTH

Near surface HABITAT

Open water

This jellyfish produces bioluminescent light shows, which are often admired from passing boats, but it also has a reputation as a ferocious stinger. As well as having eight stinging tentacles, it is covered in tiny red spots that are bundles of stinging cells. The sting is painful but not dangerous. The mauve

OCEAN LIFE

DISTRIBUTION Northeastern Atlantic, Mediterranean, Indian Ocean, and western and central Pacific

stinger glows by producing luminous mucus from surface cells when it is knocked or disturbed by waves. Hanging down from the underside of the mushroom-shaped bell are four long, frilly mouth lobes, which are sometimes called oral arms. These also have stinging cells that paralyze and entangle small planktonic animals. Sticky mucus holds the prey, which is then passed up grooves in the arms and into the mouth. Unlike most jellyfish, the life cycle of the mauve stinger does not involve a fixed stage. Eggs and sperm are shed into the water, where the eggs are fertilized and develop into tiny, oval planula larvae covered in hairlike cilia. The planula larva changes directly into a tiny, lobed, saucer-shaped medusa called an ephyra, which gradually develops into an adult.

264

ANIMAL LIFE CLASS SCYPHOZOA

Upside-down Jellyfish Cassiopea xamachana DIAMETER

Up to 12 in

(30 cm) DEPTH

0–33 ft (0–10 m)

Coastal mangroves

HABITAT

DISTRIBUTION

Tropical waters of Gulf of Mexico and

Caribbean

Divers who find this jellyfish upsidedown on the seabed often think they have found a dying specimen. However, the upside-down jellyfish lives like this, floating with its bell pointing downward and its eight large,

branching mouth arms held upward. The mouth arms have elaborate fringes consisting of tiny bladders filled with minute single-celled algae called zooxanthellae. The algae need light to photosynthesize, and the jellyfish behaves as it does in order to ensure its passengers can thrive. Excess food manufactured by the algae is used by the jellyfish, but it can also catch planktonic animals with stinging cells on the mouth arms. Its bell pulsates to create water currents that bring food and oxygen. When it wants to move, the upside-down jellyfish turns the right way up with the bell uppermost. A very similar jellyfish, Cassiopeia andromeda, is found in the tropical Indian and Pacific Oceans and may actually be the same species.

CLASS CUBOZOA

Box Jellyfish Chironex fleckeri DIAMETER

Up to 10 in (25 cm) DEPTH

Near surface HABITAT

Open water Tropical waters of southwest Pacific and eastern Indian Ocean

DISTRIBUTION

A sting from the box jellyfish can kill a person in only a few minutes, and this small animal is considered one of the most venomous in the ocean. At each corner of its box-shaped, transparent body is a bunch of 15 tentacles. When it is hunting prey such as shrimp and small fish in shallow water, the tentacles extend up to 10 ft (3 m), and swimmers can be stung without ever seeing the jellyfish. In the middle of each flattened side is a collection of sense organs including some remarkably complex eyes. The exact range of this jellyfish in the Indo-Pacific region north of Australia is not known, but other smaller, less dangerous box jellyfish also occur in the Indian and Pacific oceans. Some sea turtles can eat the box jellyfish without being affected by its sting. HUMAN IMPACT

LETHAL VENOM The sting of a box jellyfish causes excruciating pain and skin damage and can leave permanent scars. In severe cases, death may occur from heart failure or drowning following loss of consciousness. A box jellyfish antivenin is available in Australia. In northern parts of the country, some beaches are closed to the public for periods between November and April when the jellyfish are most abundant.

CLASS ANTHOZOA

Organ Pipe Coral Tubipora musica DIAMETER

Up to 20 in (50 cm) DEPTH

15–65 ft (5–20 m) HABITAT

Tropical reefs Tropical reefs of Indian Ocean and western Pacific

DISTRIBUTION

CLASS ANTHOZOA

Mushroom Leather Coral

CLASS ANTHOZOA

Dead Man’s Fingers Alcyonium digitatum

Sarcophyton species

HEIGHT

Up to 8 in (20 cm)

DIAMETER

DEPTH

Up to 5 ft (1.5 m)

0–165 ft (0–50 m)

DEPTH

HABITAT

0–165 ft (0–50 m) HABITAT

Rocks and reefs Tropical waters of Red Sea, Indian Ocean, and western and central Pacific

Rocks and wrecks Temperate and cold waters of northeastern Atlantic

DISTRIBUTION

OCEAN LIFE

DISTRIBUTION

This distinctive soft coral has a conspicuous bare stalk topped by a wide, fleshy cap covered in polyps. When the colony is touched or is resting, the polyps are withdrawn into the fleshy body, and it looks and feels like leather. Within this genus there are many similar species.

This soft coral’s strange name comes from its appearance when thrown ashore by storms. It is shaped like a thick lump with stubby fingers, which can, with a little imagination, resemble a corpse’s hand. When alive, it grows attached to rocks in shallow water and often covers large areas, especially where strong currents bring plenty of planktonic

Although the Organ Pipe Coral has a hard skeleton, it is not a true stony coral. Instead, it belongs to a group of cnidarians called octocorals, which includes soft corals and sea fans. Its beautiful red skeleton is made up of parallel tubes joined by horizontal links, and bits of this animal’s skeleton are often found washed up on tropical shores. A single polyp extends from the end of each tube, and when the polyps expand their eight branched tentacles to feed, the skeleton cannot be seen. food. With the polyps extended, the colonies have a soft, furry look. Most dead man’s fingers colonies are white but some, like those shown below, are orange with white polyps. Over the fall and winter, the colony retracts its polyps and becomes dormant. In the spring, the outer skin is shed, along with any algae and other organisms that have settled on it.

CNIDARIANS

265

CLASS ANTHOZOA

Carnation Coral Dendronephthya species HEIGHT

Up to 12 in (30 cm) DEPTH

33–165 ft (10–50 m) HABITAT

Coral reefs DISTRIBUTION Tropical reefs of Red Sea, Indian Ocean, and western Pacific

Carnation corals are among the most colorful of all reef animals. They grow as branched and bushy colonies and often cover steep reef walls with pink, red, orange, yellow, and white patches. They prefer to live where there are fast currents. When the current is running, they expand to full size and the polyps, which are on the branch ends, extend out to feed. With little or no current, they often hang down as flaccid lumps. In some species, such as the one shown here, small slivers of colored calcium carbonate show through the body tissue. These are called sclerites and help to give the soft branches some strength. Individual species of Dendronephthya are difficult to identify visually and many species have not yet been described.

CLASS ANTHOZOA

Pulse Coral

CLASS ANTHOZOA

Common Sea Fan

Xenia species

Gorgonia ventalina HEIGHT

HEIGHT

Up to 2 in (5 cm)

Up to 6 ft (2 m)

DEPTH

DEPTH

15–165 ft (5–50 m)

15–65 ft (5–20 m)

HABITAT

HABITAT

Coral reefs

Coral reefs

DISTRIBUTION Tropical reefs of the Red Sea, Indian Ocean, and western Pacific

DISTRIBUTION

Caribbean Sea

Sea fans grow attached to the seabed and look like exotic plants. Unlike soft corals, they have a supporting skeleton that provides a framework and allows them to grow quite large. It is made mainly of a flexible, horny material

CLASS ANTHOZOA

White Sea Whip Junceella fragilis HEIGHT

Up to 6 ft (2 m) DEPTH

15–165 ft (5–50 m) HABITAT

Coral reefs DISTRIBUTION

Southwestern Pacific

Sea whips have a very similar structure to sea fans but grow up as a single tall stem. They have a very strong central supporting rod containing a lot of calcareous material as well as a flexible, horny material called gorgonin. The small polyps have eight tentacles and are placed all around the stem. White sea whips are often found in groups because they can reproduce asexually. As the whip enlarges, the fragile tip breaks off and drops onto the seabed, where it attaches and grows.

OCEAN LIFE

The most notable feature of this soft coral is the way the feathery tentacles of the polyps rapidly and continually open and close. A reef covered in Pulse Coral is alive with movement. The colonies have a stout trunk with a dome-shaped top covered with long polyps. Unlike the Mushroom Leather Coral (see opposite), Pulse Coral polyps cannot retract and disappear. The pulsating movements of the polyps may help to oxygenate the colony as well as bring food within range of their tentacles.

called gorgonin and consists of a rod that extends down the inside of all except the smallest branches. In the common sea fan, the branches are mostly in one plane and form a mesh that is aligned at right angles to the prevailing current. This increases the amount of planktonic food brought within reach of the polyps, which are arranged all around the branches. Fishing nets dragged over the reef can damage common sea fans and, as they grow quite slowly, they take a long time to recolonize. They are also collected, dried, and sold as souvenirs.

266

ANIMAL LIFE CLASS ANTHOZOA

Mediterranean Red Coral Corallium rubrum HEIGHT

Up to 20 in

(50 cm) 165–650 ft (50–200 m)

DEPTH

its name, it is not a true stony coral but instead is in the same group as sea fans (see p.265). Like them, its branches are covered in small polyps, each of which has eight branched tentacles. However, the supporting skeleton is made mainly from hard calcium carbonate colored a deep red or pink. This coral is now scarce in places that are easily accessible to collectors.

Shaded rocks and caves

HABITAT

Mediterranean and warm waters of eastern Atlantic

CLASS ANTHOZOA

CLASS ANTHOZOA

Slender Sea Pen

Giant Anemone

Virgularia mirabilis

Condylactis gigantea

HEIGHT

DIAMETER

Up to 24 in (60 cm)

(30 cm)

DEPTH

DEPTH

Up to 12 in

33–1,300 ft (10–400 m)

10–165 ft (3–50 m)

HABITAT

HABITAT

Sediment

rocks

Coral reefs and

DISTRIBUTION

Temperate waters of northeastern Atlantic and Mediterranean

DISTRIBUTION

Tropical waters of Caribbean Sea and western Atlantic

The muddy bottoms of sheltered sea lochs in Scotland and Norway are often carpeted in dense beds of slender sea pens. This species has a structure similar to the orange sea pen (see below, left) but has a much thinner central stalk and thin branches. Almost half the stalk is buried in the sediment and the colony can withdraw into the sediment if disturbed.

The long, purple-tipped tentacles of this large anemone bring a splash of color to Caribbean reefs. Its columnar body is usually tucked away between rocks or corals, leaving only the stinging tentacles exposed. Several small reef fish (mainly blennies) can live unharmed among the tentacles, where they gain protection from predators. The giant anemone can move slowly along on its basal disk if it wants to find a better position on the reef.

DISTRIBUTION

Often called precious coral, Mediterranean red coral has been collected and its skeleton made into jewelry for centuries. In spite of

CLASS ANTHOZOA

Orange Sea Pen Ptilosarcus gurneyi HEIGHT

Up to 20 in (50 cm) DEPTH

33–1,000 ft (10–300 m) HABITAT

Sediment DISTRIBUTION

Temperate waters of northeastern

Pacific

Unlike the majority of anthozoans, sea pens live in areas of sand and mud. They get their name from their resemblance

to an old-fashioned quill pen. The orange sea pen consists of a central stem with branches on either side. The basal part of the stem is bulbous and anchors the colony in the sediment. Single rows of polyps extend their eight tentacles into the water from each leaflike branch, giving the front of the sea pen a downy appearance. The colony faces toward the prevailing current to maximize the flow of plankton over the feeding polyps. When no current is flowing, the colony can retract down into the sediment. Although they tend to stay in one place, colonies can relocate and re-anchor themselves if necessary. Predators of sea pens include sea slugs and starfish.

CLASS ANTHOZOA

Beadlet Anemone Actinia equina DIAMETER

acrorhagi containing stinging cells

Up to 23/4 in (7 cm) DEPTH

OCEAN LIFE

0–65 ft (0–20 m) HABITAT

Hard surfaces Coastal waters of Mediterranean, northeastern and eastern Atlantic

DISTRIBUTION

Most anemones cannot survive out of water, but the beadlet anemone can do so provided it stays damp. At low tide, this anemone can be found on rocky shores with its tentacles

retracted, looking like a blob of red or green jelly. The top of the anemone’s body is ringed with blue beads called acrorhagi. These contain numerous stinging cells, which the anemone uses to repel any close neighbors. Leaning over, it will sting any anemone within reach, and the defeated anemone will move slowly out of the victor’s territory. The beadlet anemone broods its eggs and young inside the body and ejects them through its mouth.

CNIDARIANS CLASS ANTHOZOA

CLASS ANTHOZOA

Plumose Anemone

Cloak Anemone

Metridium senile

Adamsia palliata Up to 12 in

HEIGHT

DIAMETER

(30 cm) DEPTH

2 in (5 cm)

0–330 ft (0–100 m)

HABITAT

DEPTH

0–650 ft (0–200 m)

Any hard

surface

HABITAT

Hermit crab shells DISTRIBUTION

Temperate waters of north Atlantic and north Pacific

DISTRIBUTION

Temperate waters of northeastern Atlantic and Mediterranean

This tall anemone resembles an ornate piece of architecture. It has a long column, topped by a collarlike ring and a wavy disk with thousands of fine tentacles. The most common colors are white or orange, but it can also be brown, gray, red, or yellow. Fragments from the base of large anemones can grow into tiny new anemones. The plumose anemone is often found on pier pilings and wrecks projecting out into the current.

The cloak anemone lives with its wide base wrapped around the shell of a hermit crab and its tentacles trailing beneath the crab’s head. In this position, the tentacles are ideally placed to pick up food scraps. The enveloping column of the anemone is off-white with distinct pink spots. Neither partner thrives without the other, though young cloak anemones can be found on rocks and shells between the tidemarks waiting to find a host.

ARMORED VEHICLE The hermit crab Pagurus prideaux is always seen with its protective anemone cloak. It does not have to find a bigger shell as it grows because the cloak anemone secretes a horny extension. The anemone on the crab on the left has thrown out pink stinging threads, called acontia, to repel another hermit crab.

267

CLASS ANTHOZOA

Antarctic Anemone Urticinopsis antarctica SIZE

Not recorded DEPTH

15–740 ft (5–225 m) HABITAT

Rocky sea beds Southern Ocean around Antarctica and South Shetland Islands DISTRIBUTION

Like many other Antarctic marine animals, the Antarctic anemone grows to a large size, but rather slowly. It has long tentacles with powerful stinging cells and is capable of catching and eating starfish, sea urchins, and jellyfish much larger than itself. As there are often many anemones living close together, two or more may hold a large jellyfish. As in most anemones, stinging cells on the tentacles fire barbed threads into the prey to hold it and to paralyze or kill it.

CLASS ANTHOZOA

Jewel Anemone Corynactis viridis DIAMETER 1/ 2

in (1 cm)

DEPTH

0–260 ft (0–80 m) HABITAT

Steep rocky areas Temperate waters of northeastern Atlantic and Mediterranean DISTRIBUTION

OCEAN LIFE

Jewel anemones often cover large areas of underwater cliff faces, creating a spectacular display. Individuals can be almost any color, and they reproduce by splitting in half, making two new identical anemones. This results in dense patches of differentcolored anemones. Each anemone has a small saucer-shaped disk circled by stubby translucent tentacles. The tentacles have knobbed tips that are often a contrasting color to the tentacle shafts, disk, and column of the anemone. The color combination shown here is one of the most common. Jewel anemones are not true anemones but belong to a group of anthozoans called coralliomorphs. These closely resemble the polyps of hard corals but have no skeleton. Coralliomorphs are found in all oceans but are most common in the tropics.

268

ANIMAL LIFE CLASS ANTHOZOA

Table Coral Acropora hyacinthus DIAMETER

Up to 10 ft ( 3 m) DEPTH

0–33 ft (0–10 m) HABITAT

Coral reefs Tropical waters of Red Sea, Indian Ocean, and western and central Pacific DISTRIBUTION

The magnificent flat plates of table coral are ideally shaped to expose as much of their surface as possible to sunlight. Like most hard corals, the cells of table coral contain zooxanthellae that need light to photosynthesize and manufacture food for themselves and their host. Table coral is supported on a short, stout stem that is attached to the seabed by a spreading base. The horizontal plates have numerous branches that mostly project upward from the surface, so each plate,

or table, resembles a bed of nails. Each of these branches is lined by cup-shaped extensions of the skeleton called corallites, from which the polyps extend their tentacles in order to feed, mainly at night. The usual color of table coral is a dull brown or green, but it is brightened up by the numerous reef fish that shelter under and around its plates. However, the shade the plates cast means that few other corals can live underneath a table coral. There are many other similar species that are also called table coral, but Acropora hyacinthus is one of the most abundant and widespread.

CLASS ANTHOZOA

Hump Coral Porites lobata DIAMETER

Up to 20 ft (6 m) DEPTH

0–165 ft (0–50 m) HABITAT

Coral reefs Tropical waters of Red Sea, Persian Gulf, and Indian and Pacific oceans

DISTRIBUTION

PEOPLE

CHARLIE VERON Born in Sydney, Australia, in 1945, Charlie Veron has been dubbed the “King of Coral” for his lifelong work on coral reefs. He has formally named and described over 100 new coral species, including many from the genus Acropora. His three-volume book Corals of the World is a classic text. It can be difficult to tell that hump coral is a living coral colony because it looks just like a large, lumpy rock. Closer inspection will show that the coral grows as a series of large lobes formed into a dome. The living polyps are tiny, with tentacles that are only about 1/32 in (1 mm) long, and during the day, they are hidden in their shallow skeleton cups. At night, they extend their tentacles to feed and the colony takes on a softer appearance. Hump coral is an important reefbuilding species. CLASS ANTHOZOA

Daisy Coral Goniopora djiboutiensis DIAMETER

Up to 3 ft (1 m) DEPTH

15–100 ft (5–30 m) HABITAT

Turbid reef waters

OCEAN LIFE

DISTRIBUTION Tropical waters of Indian Ocean and western Pacific

In most corals it is difficult to see the tiny polyps, but the daisy coral has polyps that are a few inches long. The head of each polyp is dome-shaped with the mouth in the middle, surrounded by a ring of about 24 tentacles. These are arranged rather like the petals of a daisy. Unlike the majority of corals, the polyps extend to feed during the day, though they will quickly withdraw if touched. Daisy coral grows as a rounded lump, but the shape is difficult to see when the polyps are extended. While most corals need clear water to survive, this species often covers large areas where the water is made turbid by disturbed sediment.

269 CLASS ANTHOZOA

CLASS ANTHOZOA

Mushroom Coral

Giant Brain Coral

Fungia scruposa

Colpophyllia natans Up to 16 ft

DIAMETER

DIAMETER

Up to 1 in (2.5 cm)

(5 m)

DEPTH

DEPTH 3–180 ft (1–55 m)

0–80 ft (0–25 m)

HABITAT Seaward side of coral reefs

HABITAT

Sediment and rubble DISTRIBUTION Tropical waters of Red Sea, Indian Ocean, and western Pacific

DISTRIBUTION

Mushroom coral is unusual in that it lives as a single individual rather than a colony. Juveniles start life as a small stalked disk attached to dead coral or rock. By the time they reach about 11/2 in (4 cm) in diameter, they become detached. The animal feeds at night and the tentacles are withdrawn during the day, leaving the skeleton clearly visible, with the mouth at the center of the disk. The skeleton resembles the gills of a mushroom. Mushroom coral uses its tentacles to turn itself the right way up if it is overturned by waves.

This huge coral grows as giant domes or extensive thick crusts and can live for more than 100 years. The surface of the colony is a convoluted series of ridges and long valleys, as in other species of brain coral, and this is what gives it its name. The valleys and ridges are often differently colored and the ridges have a distinct groove running along the top. Typically, the valleys are green or brown and the ridges are brown. The polyp mouths are hidden in the valleys and the tentacles are only extended at night. In recent years, giant brain corals in the Tortugas Islands (south of the Florida Keys) have been attacked by a disease and some have died. Particularly large colonies are popular tourist attractions in islands such as Tobago. As well as attracting divers, the coral heads attract fish, and some gobies live permanently on the coral.

CLASS ANTHOZOA

Dendrophyllid Coral Dendrophyllia species HEIGHT

Up to 2 in (5 cm) DEPTH

10–165 ft (3–50 m) HABITAT

Steep rock faces Tropical waters in Indian Ocean and from western Pacific to Polynesia DISTRIBUTION

Tropical waters of Gulf of Mexico

and Caribbean

With their large, flamboyant polyps, corals of the genus Dendrophyllia look more like an anemone than a coral. Dendrophyllids belong to a group called cup corals. They grow as a low-branching colony with each tubular individual distinct, and they do not develop the massive skeleton of reef-building corals. They have no zooxanthellae and grow in shaded parts of reefs such as below overhangs and especially on steep cliff faces. During the day, the polyps are entirely rock or even a shipwreck. When the tentacles are expanded, these tiny corals look just like anemones, with each tapering, transparent tentacle ending in a small knob. Devonshire cup coral occurs in a variety of colors from white to orange.

CLASS ANTHOZOA

Devonshire Cup Coral Caryophyllia smithii

withdrawn and the coral looks like a dull reddish lump. As darkness falls, the polyps expand their orange tentacles to feed on plankton and make a spectacular display that often covers large areas. This genus of coral is very difficult to identify to species level and can also be confused with cup corals belonging to the genus Tubastrea. CLASS ANTHOZOA

Lophelia Coral Lophelia pertusa DIAMETER

At least 33 ft (10 m)

DIAMETER

DEPTH

11/4 in (3 cm)

165–10,000 ft (50–3,000 m)

DEPTH

0–330 ft (0–100 m) HABITAT

Rocks and

Deep-sea reefs

DISTRIBUTION

While most corals grow as colonies in tropical waters, the Devonshire cup coral is solitary and lives in temperate parts of the ocean. It grows with its cup-shaped skeleton attached to a

Lophelia reefs more than 8 miles (13 km) long and 100 ft (30 m) high have been recorded off the coast of Norway. Because it lives in deep, dark water, this cold-water coral has no zooxanthellae to help build its white, branching skeleton. It therefore grows

OCEAN LIFE

wrecks Northeastern Atlantic and Mediterranean

HABITAT

Atlantic, eastern Pacific, and western Indian Ocean; distribution not fully known DISTRIBUTION

very slowly, and such large reefs are many hundreds of years old. Each polyp has 16 tentacles, which it uses to capture prey such as zooplankton and even krill from the passing current. Stinging cells render the prey immobile and it is then transferred to the mouth. In recent years many of these slow growing reefs have been badly damaged by trawlers trying to catch deep-sea fish.

270

ANIMAL LIFE CLASS ANTHOZOA

White Zoanthid Parazoanthus anguicomus HEIGHT

1 in (2.5 cm)

65–1,300 ft (20–400 m) DEPTH

Shaded rocks, wrecks, and shells

HABITAT

DISTRIBUTION

Temperate waters of northeastern

Atlantic

Most zoanthids are found in tropical waters, but the white zoanthid is common in the north Atlantic. Its white polyps arise from an encrusting base and it has two circles of tentacles around the mouth. One circle is usually held upward while the other lies flat. As well as covering rocks and wrecks, this species also encrusts worm tubes and Lophelia reefs (see p.179).

CLASS ANTHOZOA

CLASS ANTHOZOA

Whip Coral

Bushy Black Coral

Cirrhipathes species

Plumapathes pennacea

LENGTH

HEIGHT

Up to 3 ft (1 m)

Up to 5 ft (1.5 m)

DEPTH

DEPTH

10–165 ft (3–50 m)

15–1,100 ft (5–330 m)

HABITAT

Coral reefs Tropical waters of eastern Indian Ocean and western Pacific DISTRIBUTION

Whip corals, or wire corals, belong to a group of anthozoans called antipatharians to which the black corals (see right) also belong. Whip coral grows as a single unbranched colony that can be either straight

branches. Made of a tough, horny material, the skeleton is valuable as it can be cut and polished to make jewelry, although this species is not widely used for this purpose.

HABITAT

or coiled as in the species belonging to the genus Cirripathes shown here (whip corals are difficult to identify and many species remain undescribed). The feeding polyps of whip corals and black corals can be seen easily because, unlike sea fans, they cannot retract their short, pointed tentacles. Gobies live among the tentacles, hanging onto the coral with suckerlike pelvic fins.

Coral reefs Tropical waters of Gulf of Mexico, Caribbean Sea, and western Atlantic

DISTRIBUTION

Bushy black coral grows as a plantlike colony with branches shaped like large bird feathers. There are many different species of black corals, and they get their name from the strong black skeleton that strengthens their

CLASS ANTHOZOA

Tube Anemone Cerianthus membranaceus HEIGHT

14 in (35 cm) DEPTH

33–330 ft (10–100 m) HABITAT

Muddy sand

OCEAN LIFE

DISTRIBUTION

Mediterranean and northeast Atlantic

The long, pale tentacles of the tube anemone make a spectacular display but at the slightest disturbance, the animal will disappear down its tube in an instant. Tube anemones look superficially like true anemones but are more closely related to black corals (see above). They live in tubes made of sediment-encrusted mucus that can be up to 3 ft (1 m) long even though the animals are only about a third of this length. The slippery lining of the tube allows the animal to retreat rapidly. As well as about 100 long, slender outer tentacles, the animal has an inner ring of very short tentacles surrounding the mouth. The outer tentacles may look dangerous, but the tube anemone feeds only on plankton and suspended organic debris.

271

Flatworms POSSESSING VERY

thin, sometimes transparent bodies, flatworms are among KINGDOM Animalia the simplest of animals. Marine species PHYLUM Platyhelminthes mostly belong to a colorful group called Xenacoelamorpha polyclad flatworms—leaf-shaped animals, CLASSES 8 common on coral reefs. Some are found in SPECIES 20,430 fresh water, and many are parasitic. In the oceans, parasitic flukes and tapeworms are common in fish, mammals, and birds. Most flatworms belong to the phylum Platyhelminthes but acoel flatworms (see below) are now separated into the phylum Xenacoelomorpha (or Acoelomorpha). DOMAIN Eucarya

FOOD SEARCH

This polyclad flatworm is searching for food using simple eyespots and chemical receptors on the margins of its head.

Anatomy

Reproduction

The flatworm has a simple, solid structure with no internal cavity. It is so thin that oxygen can diffuse in from the water, and there are no blood or circulatory systems. The head end contains sense organs; advanced species have primitive eyes. The gut opens to the outside at one end, the opening serving as both mouth and anus. In polyclad flatworms, this opening is in the middle underside BODY SECTION of the body. When feeding, they In flatworms, the space between the internal extend a muscular tube (pharynx) organs is filled with soft connective tissue out of the mouth to grasp their crisscrossed by muscles. food. Polyclad flatworms are dorso-ventral longitudinal covered in tiny hairs (or cilia) gut muscle muscle gut which, together with simple connective branch tissue muscles, help them to glide over almost any surface. The anatomy of tapeworms and flukes is adapted to suit their parasitic lifestyle.

Most flatworms are hermaphrodites, so every individual has both ovaries and testes. The reproductive system is complex for such a primitive animal and includes special chambers and tubules where the ripe eggs are fertilized. When two polyclad flatworms meet, they may briefly touch heads and bodies in a short ritual before mating. After mating, the eggs are released into the water, laid in sand, or stuck to rocks. In some flatworms, the eggs develop directly into juvenile worms but in others they develop initially into an eight-lobed planktonic larva. Called Müller’s larva, it swims for a few days and then settles onto COMPLEX APPARATUS Some flatworms undetake the seabed and flattens “penis fencing,” where out into a young each tries to stab the other and inject sperm. flatworm.

CLASS ACOELOMORPHA

CLASS RHABTITOPHORA

Acoel Flatworm

Candy Stripe Flatworm

Waminoa species

Prostheceraeus vittatus

Less than 1/4 in

LENGTH

(5 mm) DEPTH

LENGTH

Not recorded

Up to 2 in (5 cm)

On bubble coral (Pleurogyra sinuosa)

HABITAT

DISTRIBUTION

DEPTH

0–100 ft (0–30 m) HABITAT

Tropical Indian and Pacific oceans

These diminutive flatworms look like colored spots on the bubble coral on which they live. Their ultra-thin bodies glide over the coral surface as they graze, probably eating organic debris trapped by coral mucus. Acoel flatworms have no eyes and instead of a gut, they have a network of digestive cells. They are able to reproduce by fragmentation, each piece forming a new individual. The genus is difficult to identify to species level and the distribution is uncertain.

CLASS ACOELOMORPHA

Green Acoel Flatworm

Muddy rocks DISTRIBUTION Temperate waters of northeastern Atlantic and Mediterranean

Most brightly colored flatworms are found on tropical reefs, but the candy stripe flatworm is an exception and can be found as far north as Norway. Generally a cream color, it is marked with reddish brown, lengthwise stripes. The head end of its flattened, leaf-shaped body has a pair of distinct tentacles and groups of primitive eyes. As it crawls along, the flatworm pushes the edges of its body up into folds; it is also able to swim using sinuous movements of the body. Usually found in rocky areas, it has also been seen on sand.

Convoluta roscoffensis Up to 1/2 in

LENGTH

(1.5 cm) DEPTH

Intertidal

Sheltered sandy shores HABITAT

Northeastern Atlantic; probably more widespread than shown

DISTRIBUTION

flatworm on bubble coral

OCEAN LIFE

Although difficult to see individually, these flatworms show up when they collect together in puddles of water on sandy shores at low tide. Their bodies harbor tiny, single-celled algae (p. 248) that color them bright green. In warm, sunlit pools the algae can photosynthesize and pass some of the food they make to their host. These flatworms are very sensitive to vibrations and quickly disappear down into the sand if footsteps approach.

272

ANIMAL LIFE CLASS RHABDITOPHORA

Exquisite Lined Flatworm

CLASS RHABDITOPHORA

Divided Flatworm Pseudoceros dimidiatus

Pseudobiceros bedfordi

LENGTH

Up to 3 in (8 cm)

LENGTH

DEPTH

Up to 3 in (8 cm)

Not recorded

DEPTH

HABITAT

Not recorded HABITAT

Coral reefs DISTRIBUTION

DISTRIBUTION

Tropical waters of Indian and western

Pacific oceans

Tropical waters of Indian and western

Pacific oceans

Divers frequently come across this beautiful flatworm on coral reefs. Its striking pattern of pinkish transverse stripes and white dots against a black background make it easily recognizable. It is usually seen crawling over rocks in search of tunicates and crustaceans, but it is also a fairly good swimmer. Sometimes, the head end is reared up and a pair of flaplike tentacles can be seen.

CLASS RHABDITOPHORA

Thysanozoon Flatworm Thysanozoon nigropapillosum LENGTH

Up to 3 in (8 cm) DEPTH

3–100 ft (1–30 m) HABITAT

Coral reef slopes DISTRIBUTION

Coral reefs

Tropical waters of Indian and western

Pacific oceans

The highly convoluted edge of the very thin thysanozoon flatworm is prominently displayed with a white outline. The rest of the upper side

Most species of flatworms display a distinctive pattern of colors that is more or less the same in every individual. However, the color patterns of the divided flatworm vary greatly between individuals. The body is always black with an orange margin, but the width and arrangement of the yellow or white lateral stripes, zebralike bars, or narrow and wide longitudinal stripes is highly variable. These highly contrasting colors act as a warning to predators that divided flatworms are not good to eat. Like other flatworms, this species has numerous photoand chemosensitive cells in its head region, which help the worm to find food and avoid danger. of the body is black and covered in short papillae, or protuberances, each of which ends in a yellow tip. This gives the flatworm the appearance of being peppered with yellow spots. As is the case with most tropical reef flatworms, little is known of the biology of this species, but the thysanozoon flatworm has been found in association with colonial tunicates and is thought to feed on these and other colonial animals. It has been observed to swim well, rhythmically undulating its wide body. Much of what is known about this and other tropical reef flatworms has come from observations made by recreational divers and photographers. A similar species, Thyanozoon flavomaculatum, is found on Red Sea coral reefs.

CLASS RHABDITOPHORA

Imitating Flatworm Pseudoceros imitatus LENGTH

Up to 1 in (2 cm) DEPTH

Not recorded HABITAT

Coral reefs Waters around New Guinea and northern Australia, perhaps more extensive

DISTRIBUTION

The imitating flatworm has a creamy gray background color and black reticulations surrounding pale pustules.

imitation of the skin of the sea slug Phylidiella pustulosa, and the flatworm’s color pattern is also almost identical to that of the sea slug. The sea slug secretes a noxious chemical to deter potential predators, and it may be that the imitating flatworm gains protection by looking and feeling to the touch like the distasteful sea slug.

Unlike the majority of polyclad flatworms, which have a relatively smooth skin, the imitating flatworm has a bumpy surface covered in small pustules. This appearance is an SOURCE OF IMITATION

Phylidiella pustulosa is one of the most common and widespread sea slugs on Indo-Pacific reefs about 15–130 ft (5–40 m) deep.

CLASS RHABDITOPHORA

Giant Leaf Worm Kaburakia excelsa LENGTH

Up to 4 in (10 cm) DEPTH

be seen through the skin. It feeds in the same way as most polyclad flatworms, by everting its pharynx over its prey. Most intertidal flatworms in this region are only about 1 in (2 cm) long, making this species easy to identify. It is common on floating docks and in mussel beds.

Intertidal HABITAT

Under coastal rocks DISTRIBUTION

Temperate waters of northeastern

Pacific

This large, oval flatworm crawls around rocks, stones, and undergrowth on the Pacific shores of North America. Its color is reddish-brown to tan, marked with darker spots, and when it is fully spread out, the branches of its digestive system may

CLASS CESTODA

Broad Fish Tapeworm OCEAN LIFE

GOOD IMITATION

Diphyllobothrium latum LENGTH

Up to 33 ft (10 m) DEPTH

Dependent on host HABITAT

Parasitic DISTRIBUTION

host species

Probably worldwide, dependent on

Some flatworms, including tapeworms, have become highly modified and live as parasites. The broad fish tapeworm has a complex life history. It begins life as a fertilized egg that is eaten by tiny freshwater crustaceans, inside which the larvae hatch. Freshwater, estuarine, and migratory marine fish, (such as salmon) become infected by the larvae when they eat either the crustaceans or other infected fish. The adult tapeworm lives in fish-eating mammals and may infect humans who eat raw fish. Other tapeworm species live as adults in the guts of marine fish.

RIBBON WORMS

Ribbon Worms ALSO CALLED NEMERTEAN

DOMAIN Eucarya

worms, KINGDOM Animalia ribbon worms can reach great lengths PHYLUM Nemertea of at least 160 ft (50 m), although many are small and inconspicuous. CLASSES 2 While they are commonly slightly SPECIES 1,358 flattened, the longest are cylindrical and are often called bootlace worms. The majority of ribbon worms live in the sea under rocks, among undergrowth or in sediment, and some are parasitic. A few species live inside the shells of mollusks and crabs.

Anatomy

stylet

proboscis

273

nerve ganglion nerve

Nemertean worms have a long, excretory unsegmented body with strong muscles in organs the body wall that can shorten the worm to a proboscis sheath fraction of its full length. Unlike flatworms, ribbon worms have blood vessels and a complete gut with blood vessel mouth and anus. It is often difficult to distinguish ovary between the front and rear end of the worm, but most species have many simple eyes at the front. The most characteristic feature of these worms is a strong, tubular structure called a proboscis that lies in a sheath above gut the gut. It can be thrust out by hydrostatic pressure, either through the mouth or a separate SECTION opening, and is used to capture prey. BODY Ribbon worms have no body cavity In some species, the proboscis is or gills; a simple circulatory system armed with a sharp stylet. carries oxygen around the body.

Reproduction

WARNING PATTERN

Some ribbon worms have bright patterns that may serve as a warning to predators that they are toxic. Drab-colored species only emerge at night to hunt.

CLASS ANOPLA

Football Jersey Worm Tubulanus annulatus LENGTH

Up to 30 in

(75 cm) 0–130 ft (0–40 m)

DEPTH

Gravel, stones, and sediment

HABITAT

DISTRIBUTION Cold and temperate waters of north Atlantic and north Pacific

One of the most strikingly colored ribbon worms, the football jersey worm has a patterning of longitudinal white lines and regularly spaced white rings. It may be found lying in an untidy pile beneath stones on the lower shore and may also be seen scavenging when the tide is out. More usually it lives below the shore on almost any type of seabed, including mud, sand, and shell gravel. To camouflage itself, it secretes a mucous tube that becomes covered in surrounding sediment.

Most marine ribbon worms have separate sexes and their numerous, simple gonads produce either eggs or sperm. These are usually shed into the sea through pores along the sides of the body. Some species cocoon themselves together in a mucous net where the eggs are duly fertilized. In some types of ribbon worms, the eggs develop directly into juvenile worms, while others initially hatch into various types of larvae. The long, fragile bodies of ribbon worms tend SWIMMING LARVA to break easily but they have the useful Some ribbon worms ability to regenerate any lost parts. Some develop from a species even use regeneration as a method planktonic larva called a pilidium. It is able to of asexual reproduction, where the body swim by beating hairlike breaks up into several pieces and each structures, called cilia. piece develops a new head and tail.

CLASS ANOPLA

Bootlace Worm Lineus longissimus LENGTH

Up to 180 ft (55 m) DEPTH

Intertidal HABITAT

Sediments and stones DISTRIBUTION

Temperate waters of northeast

Atlantic

The bootlace worm makes up for its rather drab brown color by its incredible length. Only a fraction of an inch in diameter, it reaches at least 33 ft (10 m) in length, and is one of the longest animals known. On the shore it appears as a writhing mass of knots lying on muddy sediment beneath boulders. Like all anoplan worms, it has its mouth behind the brain. This worm is difficult to pick up, because it exudes large amounts of mucus when handled.

CLASS ENOPLA

Ribbon Worm Nipponnemertes pulcher LENGTH

Up to 31/2 in

(9 cm) DEPTH 0–1,900 ft (0–570 m)

Coarse sediments

HABITAT

DISTRIBUTION Temperate and cold waters of Arctic, Atlantic, Pacific and Southern oceans

beneath. This species has a distinctive, shield-shaped head with numerous eyes along its edges. The number of eyes increases with age. It is usually seen when dredged up by scientists from the coarse sediments in which it lives, but is sometimes found beneath stones on the lower shore. Its full distribution is unknown.

OCEAN LIFE

This worm belongs to a class of nemertean worms called enoplan ribbon worms, whose mouth is located in front of the brain. Nipponnemertes pulcher has a short, stout body with a width of up to 1/4 in (5 mm) that tapers to a pointed tail. The coloration varies from pink to orange or deep red and is paler

274

ANIMAL LIFE

Segmented Worms SEGMENTED WORMS

include two familiar, predominantly land-based KINGDOM Animalia and freshwater groups, the earthworms PHYLUM Annelida and the leeches. In the oceans, a third CLASSES 2 group, the bristleworms or polychaetes, are numerous and diverse. These SPECIES 15,000 include burrowing lugworms, free-living predatory ragworms, and tube-dwelling worms. All segmented worms share one main characteristic—the long, soft body is divided into a series of almost identical, linked segments. DOMAIN Eucarya

BRISTLEWORM

Fire worms have long, sharp bristles on each body section. These break off if the worm is attacked and can cause severe skin irritation.

Anatomy

Reproduction

Each body segment is called a metamere and, except for the head and tail tip, all are virtually indistinguishable from each other. In bristleworms, flattened lobes (parapods) project from the sides of each segment, and are reinforced by strong rods made of chitin. The worm uses parapods for locomotion, parapod and projecting bundles of bristles help it to grip. Internally, the segments are separated ventral by partitions and filled with fluid. nerve The gut, nerve cord, and large blood cord nerve vessels run all along the body.

In most polychaete worms, the sexes are separate and the eggs and sperm are shed into the water. Spawning is usually seasonal, especially at temperate latitudes. In many species, the fertilized egg develops into a larva (trochophore) that resembles epitoke a tiny spinning top. It floats and swims in the plankton, propelled by the beating of hairlike cilia around its middle. Eventually, the larva elongates and constricts into segments as it turns into an adult. Some species brood their eggs until the larvae are well developed. Many polychaete worms change shape as they become sexually mature, becoming little more than swimming READY TO BURST bags of eggs or sperm. The egg- or sperm-laden Known as epitokes, they epitoke of a palolo worm swarm, burst open to release separates from the front the eggs or sperm, then die. segments, and bursts open.

ganglion

epidermis

BODY SECTIONS

intestine

Most segments containexcretory organ their own organs, including excretory and(nephridium) reproductive organs, and branches from the main blood vessels and ventral nerve cord.

dorsal blood vessel segmental blood vessel

JAWS OF A PREDATOR

This bobbit worm seizes prey using a proboscis tipped with sharp mandibles, which it shoots out from the mouth. excretory organ (nephridium)

parapod ventral nerve cord

CLASS POLYCHAETA

CLASS POLYCHAETA

Lugworm

Sea Mouse

Arenicola marina

Aphrodita aculeata LENGTH

LENGTH

Up to 8 in (20 cm)

Up to 8 in (20 cm)

DEPTH

DEPTH

Shore and just below

Shallow to moderate

HABITAT

HABITAT

Muddy sand

Sand, muddy sand Temperate coastal waters of northeastern Atlantic and Mediterranean

Temperate shores of northeastern Atlantic, Mediterranean, and western Baltic

DISTRIBUTION

OCEAN LIFE

DISTRIBUTION

One of the most familiar sights on western European beaches is the neat, coiled casts of undigested sand deposited by lugworms. The worm itself is rarely seen, remaining hidden in its U-shaped tube beneath the surface of the sand. The entrance to the tube is marked by a shallow, saucer-shaped depression in the sand. The worm may be pink, red, brown, black, or green. The first six segments of its front section are thick with bristles, while the next thirteen segments have red, feathery gills. The rear third of the body is thin, with no gills or bristles. Lugworms feed by eating sand, extracting organic matter from it, and expelling the waste.These fleshy worms are a favorite food of many wading birds and are also used by fishermen as bait.They are most abundant at mid-shore level in sediments containing reasonable amounts of organic matter.

CLASS POLYCHAETA

Green Paddle Worm Eulalia viridis LENGTH

Up to 6 in (15 cm)

Shore and shallows

DEPTH

Rocky areas under stones, in crevices

HABITAT

DISTRIBUTION Temperate coastal waters of northeastern Atlantic

Although this beautiful green worm is usually found crawling over rocks, it can also swim well. The name paddle worm comes from the large, leafshaped appendages called parapodia that are attached to the side of each

body segment and aid in swimming. The head has two pairs of stout tentacles on each side, a single tentacle on top, and four short, forwardpointing tentacles at the front. These tentacles and two simple black eyes help the worm in its hunt for food. The green paddle worm is attracted to dead animals, especially mussels and barnacles, but will also hunt for live prey. However, unlike the king ragworm (opposite), it does not have jaws to tackle large prey. Instead, carrion and debris sticks to its proboscis and is wiped off inside the mouth. During spring, the green paddle worm lays gelatinous green egg masses about the size of a marble on the shore and in shallow water, attaching them to seaweeds and rocks.

The segmented structure of this pretty worm can be seen only if it is turned over, because its back is disguised by a thick felt of hairs that mask its segments. Running along each side of its body are numerous stiff, black bristles and a fringe of beautiful, iridescent hairs that glow green, blue, or yellow. The bristles can cause severe irritation if they puncture the skin. The sea mouse is so called because it looks like a bedraggled mouse when washed up dead on the seashore.

SEGMENTED WORMS CLASS POLYCHAETA

WORM REEFS

King Ragworm Alitta virens LENGTH

Up to 20 in (50 cm) DEPTH

Shore and shallows HABITAT

Muddy sand Temperate coastal waters of northeastern and northwestern Atlantic DISTRIBUTION

This large worm has strong jaws that are easily capable of delivering a painful bite to a human. The jaws are pushed out on an eversible proboscis and are used for pulling food into its mouth as well as for defending itself. The king ragworm lives in a mucuslined burrow in the sand, and waits for the tide to come in before coming out to feed. It swims well by bending its long body into a series of S-shaped curves. Fishermen collect it for bait.

crown of spines in three concentric rings

CLASS POLYCHAETA

Honeycomb Worm Sabellaria alveolata LENGTH

Up to 11/2 in

DEPTH Shore and shallows HABITAT Mixed rock and sand areas

Intertidal areas of northeastern Atlantic and Mediterranean

DISTRIBUTION

Magnificent Feather Duster Sabellastarte magnifica LENGTH

Up to 6 in (15 cm) DEPTH

3–65 ft (1–20 m) HABITAT

Coral reefs DISTRIBUTION Shallow waters of the western Atlantic and Caribbean

Honeycomb worms build their tubes by gluing together sand grains stirred up by waves. The glue is a mucus secreted by the worm, which uses a lobed lip around its mouth to fashion the tube. As new worms settle out from the plankton to build their own tubes, a reef develops and expands sideways and upward, provided there is a good supply of sand. These structures provide a home to many other species. LIVE REEF

fingerlike gills on each body segment

(4 cm)

CLASS POLYCHAETA

275

Live reefs will survive for many years provided new larvae settle and grow to replace wave-damaged areas and dead worms.

Although honeycomb worms are tiny, the sand tubes they build may cover many yards of rock in rounded hummocks up to 20 in (50 cm) thick. The worms build their tubes close together, and the tube openings give the colony a honeycomb appearance. This worm’s head is crowned by spines and it has numerous feathery feeding tentacles around the mouth, which it uses to trap plankton. The body ends in a thin, tubelike tail with no appendages.

The only part of this worm that is normally visible is a beautiful fan of feathery tentacles. The worm’s segmented body is hidden inside a soft, flexible tube that it builds tucked beneath rocks or in a coral crevice or buried in sand. The tentacles are in two whorls and are usually banded brown and white. They are normally extended into the water to filter out plankton, but at the slightest vibration or disturbance, such as the exhalation of a scuba diver, the worm instantly retracts the tentacles down into the safety of the tube.

CLASS POLYCHAETA

Pompeii Worm Alvinella pompejana LENGTH

Up to 4 in (10 cm)

6,500–10,000 ft (2,000–3,000 m)

DEPTH

Hydrothermal vent chimneys

HABITAT

DISTRIBUTION

CLASS POLYCHAETA

Christmas Tree Worm Spirobranchus giganteus LENGTH

Up to 11/4 in

(3 cm) DEPTH 0–100 ft (0–30 m) or more HABITAT

Living coral

heads DISTRIBUTION

Shallow reef waters throughout

the tropics

This extraordinary worm lives in thin tubes massed together on the sides of chimneys of deep-sea hydrothermal vents. The tubes are close to the chimneys’ openings, where water from deep inside Earth pours out at temperatures of up to 660˚F (350˚C). The temperature within the worm tubes reaches 176˚F (80˚C). At its head end, the Pompeii worm has a group of large gills and a mouth surrounded by tentacles. Each of the worm’s body segments has appendages on the side called parapodia. The posterior parapodia have many hairlike outgrowths that carry a mass of chemosynthetic bacteria. The bacteria manufacture food that the worm absorbs, and the worm also eats some of the bacteria.

OCEAN LIFE

Many large coral heads in tropical waters are decorated with Christmas tree worms, which occur in a huge variety of colors. The worm lives in a calcareous tube buried in the coral and extends neat, twin spirals of feeding tentacles above the coral surface. If disturbed, the worm pulls back into its tube in a fraction of a second. For added safety, the worm can also plug its tube with a small plate called an operculum.

Eastern Pacific

276

ANIMAL LIFE

Mollusks AMONG THE MOST SUCCESSFUL

of all marine animals, mollusks display great diversity and a remarkable range KINGDOM Animalia of body forms, allowing them to live almost everywhere PHYLUM Mollusca from the ocean depths to the splash zone. They include CLASSES 8 oysters, sea slugs, and octopuses. Most species have shells SPECIES 73,682 and are passive or slow-moving; some lack eyes. Others are intelligent, active hunters with complex nervous systems and large eyes. Filter-feeding mollusks, such as clams, are crucial to coastal ecosystems, as they provide food for other animals and improve water quality and clarity. Many mollusks are commercially important for food, pearls, and their shells. DOMAIN Eucarya

Anatomy Most mollusks have a head, a soft body mass, and a muscular foot. The foot is formed from the lower body surface and helps it to move. Mollusks have what is called a hydrostatic skeleton—their bodies are supported by internal fluid pressure rather than a hard skeleton. All mollusks have a mantle, a body layer that covers the upper body and may or may not secrete a shell. The shell of bivalves (clams and relatives) has two halves joined by a hinge; these can be held closed by powerful muscles while the tide is out, or if danger threatens. Mollusks other than bivalves have a rasping mouthpart, or radula, which is unique to mollusks. Cephalopods (octopuses, squid, and cuttlefish) also have beaklike jaws as well as tentacles, but most lack a shell, while most gastropods (slugs and snails) have a single shell. This is usually a spiral in snails, but can be cone-shaped in other forms, such as limpets. gill

The tropical giant clam is the largest bivalve and may measure more than 3 ft (1 m) across and weigh over 440 lb (220 kg).

GASTROPOD ANATOMY

spiral shell

mantle cavity

sensory tentacle

digestive system

eye SPIRAL SNAIL SHELL

muscular foot

radula hinge ligament

BIVALVE ANATOMY

Bivalves are housed within a shell of two halves (right) from which the siphons and muscular foot can be extended. The shell is opened and closed by the adductor muscles, labeled in the body plan (far right).

REEF-DWELLING GOLIATH

The body plan (far left) of gastropods (slugs and snails) features a head, large foot, and usually a spiral shell (left). In shelled forms, all the soft body parts can be withdrawn into the shell for protection, or to conserve moisture while uncovered by the outgoing tide.

shell mantle cavity

digestive system

siphon

muscular foot BIVALVE SHELL gill

adductor muscle

jaws feeding arm

OCEAN LIFE

radula digestive system

eye arm

internal shell

siphon gill

mantle cavity

CEPHALOPOD ANATOMY

Cephalopods have large eyes, in front of which there are a number of tentacles. The siphon functions in respiration and in rapid movement. Some forms have a flattened internal shell.

MOLLUSKS

Sense Organs

277

HUMAN IMPACT

Touch, smell, taste, and vision are well developed in many mollusks. The nervous system has several paired bundles of nervous tissue (ganglia), some of which operate the foot, and interpret sensory information such as light intensity. Photoreceptors range from the simple eyes (ocelli) seen along the edges of the mantle or on bivalve siphons, to the sophisticated image-forming eyes of cephalopods. Cephalopods are also capable of rapidly changing their color. PIGMENTED SKIN CELLS HELP CUTTLEFISH TO CHANGE COLOR

GRAFTING OYSTERS Pearls form in oysters when a grain of sand or other irritant lodges in their shells. The oyster coats the grain with a substance called nacre, forming a pearl. Today many pearls are cultured artificially: the shell is opened just enough to introduce an irritant into the mantle cavity. SEEDING AN OYSTER

The best-shaped artificial pearls are produced by “seeding” oysters with a tiny pearl bead and a piece of mantle tissue from another mollusk .

1

The giant cuttlefish’s color change is due to skin cells called chromatophores. It is pale when pigment is confined to a small area of each cell.

When the cuttlefish passes over a darker background, it disperses the colored pigments throughout each of its chromatophores, and the animal darkens.

2

MOLLUSCAN BEAUTY

Displaying fabulous warning colors, this nudibranch is a shell-less example of the many thousands of marine species of gastropods (slugs and snails).

Movement Mollusks move in many different ways. Most gastropods glide across surfaces using their mucus-lubricated foot. Exceptions include the sea butterfly, which has a modified foot with finlike extensions for swimming. Some bivalves, such as scallops, also swim, producing jerky movements by clapping the two halves of their shell together. Other bivalves burrow by probing with their foot and then pulling themselves downward by muscular action. Cephalopods are efficient swimmers; some have fins on the sides of their bodies that let them hover in the water, and they can accelerate rapidly by squirting water out through their siphons.

siphon

REDUCING DRAG

Swimming backward reduces drag from the tentacles. The siphon, used for jet propulsion, is clearly visible in this Humboldt squid.

AIDED BY MUCUS

Muscular contractions ripple through the fleshy foot of this marine snail. It secretes a lubricating mucus that helps it to move on rough surfaces.

Respiration Most mollusks obtain oxygen from water using gills, called ctenidia, which are situated in the mantle cavity. These are delicate structures with an extensive capillary network and a large surface area for gaseous exchange. In species that are always submerged, water can continually be drawn in and over the gills. Those living in the intertidal zone are exposed to the air for short periods and must keep their gills moist. At low tide, bivalves clamp shut and some gastropods close their shell with a “door” (called an operculum) to retain moisture. Pulmonate snails have a simple lung formed from the mantle cavity instead of ctenidia and are mostly terrestrial but others live on the seashore and can absorb oxygen through their skin when immersed.The respiratory pigment in most molluscan blood is a copper compound called hemocyanin. It is not as efficient at taking up oxygen as external gills hemoglobin and gives mollusks’ (ctenidia) blood a blue color.

Nudibranchs (sea slugs) have feathery external gills toward the rear of their bodies. The warning coloration of this species includes the bright orange gills.

OCEAN LIFE

COLOR CODING

278

ANIMAL LFE

Feeding

OCEAN LIFE

The ways in which molluscs feed are almost as varied as their anatomy. Sedentary molluscs, such as many bivalves including clams and oysters, create water currents through tubular outgrowths of their mantle (siphons). They filter food from the moving water with their mucus-covered gills. Suitably sized particles are then selected and passed to the mouth by bristly flaps called palps. Sea slugs, chitons, and many sea snails graze algae from hard surfaces using their rasplike radula. Radulae have tooth-like structures called denticles, many of which are reinforced with an iron deposit for durability. Larger molluscs feed on crustaceans, worms, fish, and other molluscs, which they locate either by scent or, in the case of some cephalopods such as octopuses, by sight. Cephalopods use their suckered arms to capture prey and their parrot-like beak to crush and dismember it. Some squid even appear to hunt in packs and swim in formation over reefs looking for prey.

SPECIES-SPECIFIC DENTICLES

The denticles on a mollusc’s radula are often species-specific. This electron micrograph shows the distinctive radula of the gastropod Sinezona rimuloides.

FEEDING TRAIL

Limpets continually graze the same area as the algae and bacterial film on which they feed regrow rapidly. The abrasive radula of the limpet scrapes a trail on the rock surface, as shown above.

MOLLUSCS LIMPET CHAIN

Reproduction

DEVELOPING EMBRYOS

In 4 months, Australian Giant Cuttlefish eggs develop into mini-replicas of the adults.

279

Slipper Limpets change from male to female as they grow. This chain of four such limpets has a female at the bottom and smaller males above her.

In many molluscs, reproduction simply involves releasing sperm or eggs (gametes) into the water. Fertilization is external and there is no parental care. Individuals may be of separate sexes or hermaphrodites (having both male and female reproductive organs). Hermaphrodites may function as male or female at different times or, as in nudibranchs, produce both eggs and sperm, although eggs can be fertilized only by cross-fertilization. Some species, such as slipper limpets, change sex with age, while oysters can change sex several times in a breeding season. Among cephalopods, males court females, fertilization is internal, and in some species, the eggs are protected by the females until they hatch.

Lifecycles

HUMAN IMPACT

OYSTER DEMAND Oysters have long been harvested as a food source. Their high market value and increasing demand have led to overexploitation of wild stocks. In the North Sea, the European flat oyster has vanished from much of its former range, and today most oysters are commercially farmed. SLOW RECOVERY PERIOD

Relatively long-lived and reproducing only sporadically, the European flat oyster (right) takes a long time to recover from overexploitation.

READY AND WAITING FOR PREY

This cuttlefish hovers with its arms outstretched. When prey comes within reach, the two feeding arms, currently contracted and set above the two lower arms, will shoot forward to grab the prey.

Most molluscs produce eggs that either float or are deposited in clusters, anchored to the substrate. Most forms have eggs that hatch into shell-less larvae, which live in the plankton. The larvae are called ciliated trochophores due to their bands of hair-like cilia, used in PLANKTONIC LARVA swimming. In gastropods, bivalves, The visible bands of this veliger larva of the and scaphopods, the trochophore Common Limpet beat with tiny hair-like cilia, which are used in locomotion and feeding. larvae change into veliger larvae, which have larger ciliated bands, and sometimes adult features such as a mantle or a rudimentary shell or both. As they approach maturity, the larvae float down from the surface and, on reaching the sea bed, change into adults. Only those that land in a suitable environment survive to reach sexual maturity. Cephalopod eggs hatch into active predators. Some resemble mini-adults; others live in the plankton and initially look and behave differently from the adults. SECURING EGG CLUSTERS each finger-shaped egg capsule holds up to seven eggs

This female Bigfin Reef Squid produces up to 400 egg capsules containing about 2,500 eggs. Here, she is securing egg capsules to a solid substrate.

MOLLUSC CLASSIFICATION The phylum Mollusca is the second largest animal phylum, comprising more than 73,000 species, and their diverse form has led to the identification of eight different classes. The majority of species live in marine habitats, but freshwater and terrestrial species are also numerous. MONOPLACOPHORANS Class Monoplacophora

131 species

About 30 species

These are marine, shell-less, worm-like organisms of deep-water sediments. Their horny outer layer is covered with spines.

These deep-sea molluscs lack eyes but have a radula and a cone-like shell. They are more abundant as fossils than as living species.

SOLENOGASTERS Class Solenogaster

TUSK SHELLS Class Scaphopoda

273 species

571 species

Another marine class of shell-less, wormlike organisms, solenogasters live in or on the ocean floor. Some lack a radula.

These animals have a tubular, tapering shell, open at both ends. The head and foot project from the wider end and dig in soft sediments.

CEPHALOPODS Class Cephalopoda

9,209 species

816 species

Bivalves, or clams and their relatives, have a hinged shell of two halves, but no radula. Most are sedentary and marine. Siphons create a water current through the shell, aiding feeding and respiration. Sexes are usually separate.

Squid, octopuses, and cuttlefish are all cephalopods – fast-moving and intelligent, with a complex nervous system and large eyes. The shell is internal or absent, the head surrounded by arms, with or without suckers. The central mouth has a parrot-like beak and a radula. The sexes are separate.

GASTROPODS Class Gastropoda 61,682 species

Familiar as slugs and snails, these molluscs are marine, freshwater, and terrestrial. They have a spiral shell and a large, muscular foot. The body is twisted 180º so the mantle cavity lies over the head. Many species can retract into their shell; hermaphrodite species are common.

CHITONS Class Polyplacophora 970 species

Chitons have a repeating structure with a series of plates (usually 8) on their backs enclosed by an extension of the mantle. The underside is dominated by the foot.

OCEAN LIFE

CAUDOFOVEATES Class Caudofoveata

BIVALVES Class Bivalvia

280

ANIMAL LIFE CLASS BIVALVIA

Common Mussel Mytilus edulis LENGTH

10–15cm (4–6in) HABITAT

Intertidal zones, coasts, estuaries DISTRIBUTION North and southeastern Atlantic, northeastern and southwestern Pacific

Also called the Blue Mussel, this edible, black-shelled bivalve attaches itself in large numbers to various substrates using tough fibres called byssus threads. These fibres are extremely strong and prevent the mussels from being washed away. The fibres increase in strength in autumn perhaps to cope with storms. When the mussel opens its shell, water is drawn in over the gills, or ctenidia, which absorb oxygen into the tissues and also filter food particles out of the water. Common Mussels are very efficient filter feeders – they process about 45–70 litres (10–15 gallons) of water per day and consume almost everything they trap. The sexes are separate and so grouping together in “beds” helps to ensure that their eggs are fertilized. After hatching, the planktonic larvae are dispersed by the ocean currents. After some months the larvae settle, attach, and metamorphose, but can resorb their byssus and move to a better spot.

CLASS BIVALVIA

Black-lip Pearl Oyster Pinctada margaritifera LENGTH

Up to 30cm (12in) diameter HABITAT

Hard substrata of interand subtidal zones; reefs CLASS BIVALVIA

Great Scallop

DISTRIBUTION Gulf of Mexico, western and eastern Indian Ocean, western Pacific

Black-lip Pearl Oysters begin life as a male before changing into a female two or three years later. Females produce millions of eggs, which are fertilized randomly and externally by the males’ sperm, before hatching into free-swimming larvae. The mobile larvae pass through various larval stages for about a month before eventually settling on the sea floor, after metamorphosing into the sessile (immobile) adult form. This species is famous and much sought-after because it occasionally produces prized black pearls.

Pecten maximus WIDTH

Up to 17cm (71/2 in) HABITAT

Sandy sea beds, at 5–150m (16–500ft), commonly 10m (33ft) DISTRIBUTION

CLASS BIVALVIA

Atlantic Thorny Oyster Spondylus americanus

Northeastern Atlantic

OCEAN LIFE

LENGTH

Also known as the King Scallop, the Great Scallop is usually found partly buried in sand. It is one of the few bivalves capable of rapid movement through water, which it achieves using a form of jet propulsion. It claps the two halves of its shell together, which pushes water out of the mantle cavity close to the hinge. It moves forwards with its shell gape first, producing j erky movements as it takes successive “claps” of water. These movements are a useful strategy to escape from predators. These edible bivalves are now farmed to meet growing demand.

Up to 11cm (41/2 in) HABITAT

Rocks to a depth of 140m (460ft) DISTRIBUTION Southeast coast of USA, Bahamas, Gulf of Mexico, Caribbean

The Atlantic Thorny Oyster’s spiny shell protects it from predators.The oyster pictured here is covered with an encrusting red sponge, which provides camouflage. This species is unusual in having a ball-and-socket type hinge joining the two halves of its shell,

rather than the more common toothed hinge seen in many other bivalves. The Atlantic Thorny Oyster cements itself directly to rocks rather than using byssal threads.

CLASS BIVALVIA

Shipworm Teredo navalis LENGTH

60cm (24in) HABITAT

Wood burrows in high-salinity seas and estuaries Coastal waters off North, Central, and South America, and Europe

DISTRIBUTION

Despite its worm-like appearance, the shipworm is a type of clam that has become elongated as an adaptation to its burrowing lifestyle. Its bivalve shell, situated at the anterior end, is very small and ridged. The Shipworm uses it with a rocking motion to bore into wooden objects. Outside the shell its body is unprotected, except for a calcareous tube it secretes to line the burrow. These worms damage wooden structures, such as piers, irreparably and in the past caused many ships to sink.The burrow entrance is only about the size of a pinhead, but the burrow itself may be over 1cm (1/2 in) wide, so the extent of an infestation is often underestimated until it is too late. Shipworms change from male to female during their lifetime, and the female form produces many eggs, from which free-swimming larvae hatch. When they mature and settle on a suitable piece of wood, the larvae quickly metamorphose into the adult form and start burrowing.

MOLLUSCS CLASS BIVALVIA

Common Piddock Pholas dactylus LENGTH

Up to 15cm (6in) across HABITAT

Lower shore to shallow sublittoral DISTRIBUTION South and east coasts of UK, Severn estuary in UK, west coast of France, Mediterranean

anterior beak of elliptical shell

This mollusc has a pronounced “beak” covered in tooth-like projections at the front end of its shell. It uses this feature for boring holes into relatively soft substrates, such as mud, chalk, peat, and shale. Like the Shipworm (opposite), this piddock relies on its burrows for protection from predation, because the shell does not encase all of its body – its two fused siphons (tubes for eating, breathing, and excretion) trail out behind it. The shell is fragile, elliptical, and covered in a pattern of concentric ridges and radiating lines. If disturbed, the Common Piddock has an unusual defence strategy: it squirts a luminous blue secretion from its outgoing, or exhalant, siphon. Such bioluminescence is very rare in molluscs, seen in only a few species.

fused siphons

CLASS BIVALVIA

Giant Clam Tridacna gigas LENGTH

Up to 1.5m (5ft) HABITAT

Reefs, reef flats and shallow lagoons to 20m (65ft) DISTRIBUTION Tropical Indo-Pacific from south China seas to northern coasts of Australia, and Nicobar Islands in the west to Fiji in the east

The largest and heaviest of all molluscs is the Giant Clam. Like other bivalves, it feeds by filtering small food particles

from the water using its ingoing, or inhalant, siphon, which is fringed with small tentacles. However, it differs in obtaining most of its nourishment from zooxanthellae (unicellular algae that live within its tissues) – a type of relationship also associated with coral polyps. The algae have a constant and safe environment in which to live; in return they provide the clam with essential nutrients, the carbon-based products of photosynthesis. In fact, so dependent is the Giant Clam on these algae that it will die without them. The adult is sessile (immmobile) and its inhalant and exhalant (outgoing) siphons are the only openings in its mantle. Although the scalloped edges

CLASS BIVALVIA

281

CLASS BIVALVIA

Common Edible Cockle

Atlantic Jackknife Clam

Cerastoderma edule

Ensis directus

LENGTH

LENGTH

Up to 5cm (2in)

16cm (6in)

HABITAT

HABITAT

Middle and lower shore, 5cm (2in) below surface of sand or mud

Sandy and muddy shores and shallows

DISTRIBUTION Barents Sea, eastern north Atlantic from Norway to Senegal, West Africa

DISTRIBUTION Atlantic coast of North America, introduced to North Sea

This edible bivalve has a robust, ribbed shell and burrows in dense populations just below the surface of sand or mud, filtering organic matter such as plankton from the water. Cockles are an important commercial species but also a vital food source for wading birds such as oystercatchers.

Atlantic Jackknife Clams live in deep, vertical burrows on muddy and soft, sandy shores. Native to the northeast coast of North America, the freeswimming larval stage is thought to have been introduced to the North Sea in 1978 when a ship emptied its ballast tanks outside the port of Hamburg. This clam has spread along the continental coast. In places, it affects local polychaete worm populations, but it is not considered a pest.

of their shell halves are mirror images of one another, larger individuals may be unable to close their shells fully, so their brightly coloured mantle and siphons remain constantly exposed. Many Giant Clams appear irridescent due to an almost continuous covering of purple and blue spots on their mantles, while others look more green or gold, but all have a number of clear spots, or “windows”, that allow sunlight to filter into the mantle cavity. Fertilization is external and the eggs hatch into free-swimming larvae before settling onto the sea bed.The exhalant siphon expels water and at spawning time provides an exit point for the eggs or sperm.

SPAWNING Reproduction in Giant Clams is triggered by chemical signals that synchronize the release of sperm and eggs into the water. Giant Clams start life as males and later become hermaphroditic, but during any one spawning event, they release either sperm or eggs in order to avoid self-fertilization. A large clam can release as many as 50 million eggs in 20 minutes.

OCEAN LIFE

GIANT CLAM

The giant clam grows to its huge size with the help of photosynthetic microorganisms (zooxanthellae) living in its colorful mantle tissue, which share the sugars they produce with the clam. Collected for its meat and shell, it is now rare throughout its range and international trade is restricted.

284

ANIMAL LIFE orange foot with greenish tint

CLASS GASTROPODA

Common Limpet Patella vulgata

CLASS GASTROPODA

Top Shell Tectus niloticus

DIAMETER

LENGTH

21/2 in (6 cm)

6 in (16 cm) HABITAT

HABITAT

Rocks on high shore to sublittoral zone

Intertidal and shallow subtidal areas, reef flats to 23 ft (7 m)

conical shell

MUSCULAR FOOT DISTRIBUTION Northeastern Atlantic from Arctic Circle to Portugal

Abundant on rocks from the high to the low water mark, the common limpet is superbly adapted to shore life. A conical shell protects it from predators and the elements. Limpets living at the low water mark are buffeted by the waves and so require smaller, flatter shells than those living at the high water mark, where wider,

The common limpet’s muscular foot, seen here from below, holds it firmly to its rock, regardless of the strength of the waves.

taller shells allow for better water retention during periods of exposure. Limpets travel slowly during low tide, covering up to 24 in (60 cm) using contractions of their single foot. They graze on algae from rocks using a radula (a rasplike structure), which has teeth reinforced with iron minerals.

Eastern Indian Ocean, western and southern Pacific

DISTRIBUTION

Easily distinguished from most other gastropods by the conical shape of its spiral shell, the top shell moves slowly over reef flats and coral rubble, feeding on algae. Demand for its flesh and pretty shell has led to declining numbers, especially in the Philippines, due to unregulated harvesting. It has, however, been successfully introduced elsewhere in the Indo-Pacific, such as French Polynesia and the Cook Islands, from where some original sites are being restocked.

CLASS GASTROPODA

Red Abalone Haliotis rufescens LENGTH

6–8 in (15–20 cm) HABITAT

Rocks from low tide mark to 100 ft (30 m) East Pacific coasts from southern Oregon, US to Baja California, Mexico

DISTRIBUTION

The largest of the abalone species, the red abalone is so called because of the brick-red color of its thick, roughly oval shell. There is an arc of

CLASS GASTROPODA

RETURNING HOME

Limpets gradually grind a “scar” into their anchor spot on the rock, to aid their grip and help retain water. A mucus trail leads them back to the spot.

Venus Comb Murex pecten LENGTH

Up to 3 in (8 cm) HABITAT

Tropical warm waters to 650 ft (200 m) CLASS GASTROPODA

CLASS GASTROPODA

Zebra Nerite

Dog Whelk

Puperita pupa

Nucella lapillus

DISTRIBUTION

LENGTH

LENGTH

Up to 1/2 in (1 cm)

Up to 21/2 in (6 cm)

HABITAT

HABITAT

Rocky tide pools

Middle and lower rocky shores

Caribbean, Bahamas, Florida

DISTRIBUTION

Northwestern and northeastern

OCEAN LIFE

Atlantic

The small, rounded, smooth, blackand-white striped shell of the zebra nerite is typical of the species, but in examples from Florida the shell is sometimes more mottled or speckled with black. These gastropods are most active during the day, when they feed on microorganisms such as diatoms and cyanobacteria, but if they become too hot or they are exposed at low tide, they cluster together, withdraw into their shells, and become inactive. This may be a mechanism for preventing excessive water loss. Unusually for gastropods, there are separate males and females of zebra nerites and fertilization of the eggs occurs internally. The males use their penis to deposit sperm into a special storage organ inside the female. Later, she lays a series of small white eggs that hatch into planktonic larvae.

One of the most common rocky shore gastropods, the dog whelk has a thick, heavy, sharply pointed spiral shell. The shell’s exact shape depends on its exposure to wave action, and its color depends on diet. Dog whelks are voracious predators, feeding mainly on barnacles and mussels. Once the prey has been located, the whelk uses its radula to bore a hole in the shell of its prey before sucking out the flesh.

DISTRIBUTION

Eastern Indian Ocean and western

Pacific

The tropical carnivorous snail known as the Venus comb has a unique and spectacular shell. There are rows of long, thin spines along its longitudinal ridges, which continue onto the narrow, rodlike, and very elongated siphon canal. The exact function of these spines is unknown, but they are thought to be either for protection or to prevent the snail from sinking into the soft substrate on which it lives. Its body is tall and columnar so that it can lift its cumbersome shell above the sediment to move in search of food.

three to five clearly visible holes in the shell, through which water flows for respiration.These are filled and replaced with new holes as the abalone increases in size. Sea otters are one of the red abalone’s main predators, along with human divers.

HIDING FROM VIEW There are times when the Venus comb buries itself just below the surface of the sea floor, displacing the sand with movements of its muscular foot. However, it leaves the opening of its tubular inhalant siphon above the sand’s surface so that it can draw water into its mantle cavity to obtain oxygen and to “taste” the water for the presence of prey.

HALF BURIED

The spines of this Venus comb can be seen sticking out of the sand. The siphon is visible to the right of the picture.

MOLLUSKS

285

CLASS GASTROPODA

Tiger Cowrie Cypraea tigris LENGTH

Up to 6 in (15 cm) HABITAT

Low tide to 100 ft (30 m) on coral reefs and flats

DISTRIBUTION

Indian Ocean, western Pacific

One of the largest cowrie species, the tiger cowrie has a shiny, smooth, domed shell with a long, narrow aperture, and is variously mottled in black, brown, cream, and orange. The cowrie’s mantle (its body’s outer, enclosing layer) can extend to cover parts of the exterior of the shell. These extensions have numerous projections, or papillae, whose exact function is unknown, but which may increase the surface area for oxygen absorption or provide camouflage of some sort. Tiger cowries are nocturnal creatures, hiding in crevices among the coral during the day and emerging at night to graze on algae. The sexes are separate and fertilization occurs internally. Females exhibit some parental care in that they protect their egg capsules by covering them with their muscular foot until they hatch into larvae, which then enter the plankton to mature.

CLASS GASTROPODA

Giant Triton Charonia tritonis LENGTH

Up to 16 in (40 cm) HABITAT

Coral reefs, mostly in subtidal zones

DISTRIBUTION

Indian Ocean, western and central

Pacific

CLASS GASTROPODA

Common Periwinkle Littorina littorea CLASS GASTROPODA

Flamingo Tongue Cyphoma gibbosum LENGTH

1–11/2 in (3–4 cm) HABITAT

DISTRIBUTION Western Atlantic, from North Carolina to Brazil; Gulf of Mexico, Caribbean Sea

The off-white shell of the flamingo tongue cowrie is usually almost completely hidden by the two fleshy, leopard-spotted extensions of its

LENGTH

Up to 1 in (3 cm) HABITAT

Upper shore to sublittoral rocky shores, mud flats, estuaries DISTRIBUTION Coastal waters of northwest Europe; introduced to North America

The common periwinkle has a black to dark gray, sharply conical shell and slightly flattened tentacles, which in juveniles also have conspicuous black banding. The sexes are separate and fertilization occurs internally. Females release egg capsules, containing two or three eggs,

directly into the water during the spring tides. The eggs hatch into free-swimming larvae that float in the plankton for up to six weeks. After settling and metamorphosing into the adult form, it takes a further two to three years for the adult to fully mature. It feeds mainly on algae, which it rasps from the rocks. In the 19th century, the common periwinkle was accidentally introduced into North America, where its selective grazing of fast-growing algal species has considerably affected the ecology of some rocky shores.

OCEAN LIFE

Coral reefs at about 50 ft (15 m)

body’s outer casing, or mantle. When threatened, however, its distinctive coloration quickly disappears as it withdraws all its soft body parts into its shell for protection. This snail feeds almost exclusively on gorgonian corals, which dominate Caribbean reef communities. Although these corals release chemical defenses to repulse predators, the flamingo tongue cowrie is apparently able to degrade these bioactive compounds and eat the corals without coming to any harm. After mating, the female strips part of a soft coral branch and deposits the egg capsules on it. Each capsule contains a single egg that will hatch into a free-swimming planktonic larva.

This gastropod is one of the very few animals that eats the crown-of-thorns starfish, itself a voracious predator and destroyer of coral reefs. The giant triton is an active hunter that will chase prey, such as starfish, mollusks, and sea stars, once it has detected them. It uses its muscular single foot to hold its victim down while it cuts through any protective covering using its serrated, tonguelike radula; it then releases paralyzing saliva into the body before eating the subdued prey.

286 CLASS GASTROPODA

CLASS GASTROPODA

Three-tooth Cavoline

Sea Hare

Cavolinia tridentata

Aplysia punctata

LENGTH

LENGTH

1/ 2

Up to 8 in (20 cm)

in (1 cm)

HABITAT

HABITAT

330–6,500 ft (100–2,000 m); carried in ocean currents DISTRIBUTION

CLASS GASTROPODA

Bubble Shell Bullina lineata LENGTH

1 in (2.5 cm) HABITAT

Sand, reefs to 65 ft (20 m), mainly intertidal; subtidal at range limits DISTRIBUTION Tropical and subtropical waters of Indian Ocean and west Pacific

The pale spiral shell of the bubble shell (also known as the red-lined bubble shell) has a distinctive pattern of pinkish red lines by which it can be

identified. Its soft body parts are delicate and translucent with a fluorescent blue margin and, in form, reminiscent of the Spanish dancer (opposite), which is a close relative that has lost its shell. If threatened, the bubble shell quickly withdraws into its shell and at the same time regurgitates food, possibly as a defense mechanism to distract predators. The bubble shell is itself a voracious predator, feeding on sedentary polychaete worms. This mollusk is hermaphroditic and produces characteristic spiral white egg masses.

Warm oceanic waters worldwide

This species of sea butterfly has a small, almost transparent, spherical shell with three distinctive, posterior projections. The shell also has two slits through which large extensions of the mantle pass. These brownish “wings” are ciliated and so can create weak water currents as well as aid buoyancy. Sea butterflies are unusual among shelled mollusks in that they can live in open water. Like other members of this group, the three-tooth cavoline produces a mucus web very much larger than itself, which traps planktonic organisms, such as diatoms and the larvae of other species. It eats the web and the trapped food at intervals, then produces a new one. During their lifetime, sea butterflies change first from males into hermaphrodites and then into females.

Shallow water

Northeast Atlantic and parts of the Mediterranean

DISTRIBUTION

The sea hare, a type of sea slug, has tentacles reminiscent of a hare’s ears. It has an internal shell about 11/2 in (4 cm) long that is visible only through a dorsal opening in the mantle. If disturbed, it releases purple or white ink. It is not known if this response is a defense mechanism.

CLASS GASTROPODA

CLASS GASTROPODA

Polybranchid

Hermissenda Sea Slug

Cyerce nigricans

Hermissenda crassicornis

LENGTH

Up to 11/2 in (4 cm)

LENGTH

HABITAT

Up to 3 in (8 cm)

Reefs

HABITAT

Mud flats, rocky shores DISTRIBUTION

Western Indian Ocean, western and

central Pacific

OCEAN LIFE

DISTRIBUTION

This colorful sea slug is a herbivore that browses on algae. It has no need of camouflage or a protective shell, as it has two excellent alternative defense strategies. First, it can secrete distasteful mucus, by utilizing substances in the algae it feeds on and secreting them from small microscopic glands over the body. Second, its body is covered with petal-like outgrowths called cerata, spotted and striped above and spotted below, that can be shed if it is attacked by a predator, in the same way as a lizard sheds its tail. This ability to cast off body parts to distract predators is called autotomy. The cerata are also used in respiration, their large collective surface area allowing efficient gas exchange with the surrounding water. The head carries two pairs of sensory organs— the oral tentacles near the mouth and, further back, the olfactory organs (rhinophores). These are retractile and subdivide as the polybranchid matures. They are used to assist in finding food and mates. There is some debate as to whether this sea slug is a separate species or is simply a color variation of a similar mollusk, Cyerce nigra.

CLASS GASTROPODA

Chromodorid Sea Slug Chromodoris lochi LENGTH

11/2 in (4 cm) HABITAT

Reefs

DISTRIBUTION

Tropical and subtropical western and

central Pacific

Protected from predators by its bright warning coloration and unpleasant taste, the chromodorid sea slug forages in the open, rather than hiding away

in cracks and crevices. Since it cannot swim, it glides over the tropical reefs on which it lives on its muscular foot, secreting a mucus trail much as terrestrial slugs do. The different species of the genus Chromodoris are distinguished by the pattern of black lines on their backs and the plain color of their gills and rhinophores (a pair of olfactory organs at the head end). The two chromodorid sea slugs pictured here are possibly about to mate. To do so, they must face in opposite directions so that their sexual openings are aligned. As they are hermaphrodites, they both produce sperm, which they exchange during mating, and both later produce fertilized eggs.

Northwest and northeast Pacific

This sea slug, usually known simply as Hermissenda, has an unusual way of deterring predators. It separates the stinging cells from any organism it eats and stores them in the orange-red tips of petal-like tentacles, or cerata, that cover its back. Any creature that touches the cerata is stung. Unlikely though it seems, Hermissenda is used extensively by scientists conducting memory experiments. The animal has an excellent sense of smell that enables it to find its way around mazes to locate food, and it can be “taught” to respond to simple stimuli.

MOLLUSKS CLASS GASTROPODA

Spanish Dancer Hexabranchus sanguineus LENGTH

Up to 24 in (60 cm)

exposing its bright colors and possibly startling potential predators. Spanish dancers are specialist predators that feed only on sponges, particularly encrusting species, from which they modify and concentrate certain distasteful compounds in their skin to

HABITAT

Shallow water on coasts and reefs

DISTRIBUTION

287

use as another defense against predation. They have external gills for respiration, which are extensively branched and attached to the body wall in distinct pockets and which cannot be retracted. Like all nudibranchs, the Spanish dancer is hermaphroditic, but it requires a partner in order to reproduce.

Parts of tropical Indian Ocean,

west Pacific

external gills

The largest of the nudibranchs is the Spanish dancer—so called because when it swims, the undulating movements of its flattened body are reminiscent of a flamenco dancer. Adults are brightly but variably colored, generally in shades of red, pink, or orange, sometimes mixed with white or yellow. While resting, crawling, or feeding, the lateral edges of its mantle are folded up over its back, displaying the less colorful underside. If disturbed, it will escape by swimming away,

SEA ROSE To protect its egg cluster from predators, the Spanish dancer deposits with its eggs some of the toxins that it produces for its own defense. Once hatched, the free-swimming larvae join the plankton until they mature. With a

EGG RIBBON

Each dancer produces several roselike pink egg ribbons about 1½ in (4 cm) across; together these may contain over one million eggs.

OCEAN LIFE

bright coloration

life-span of about a year, they grow rapidly, settling on a suitable food source when they are ready to change into the adult form.

288 CLASS CEPHALOPODA

CLASS CEPHALOPODA

Dumbo Octopus

Blue-ringed Octopus

Grimpoteuthis plena

Hapalochlaena maculosa

LENGTH

DISTRIBUTION

CLASS CEPHALOPODA

Nautilus Nautilus pompilius WIDTH

Shell up to 8 in (20 cm) HABITAT

Tropical open waters to 1,600 ft (500 m) DISTRIBUTION Eastern Indian Ocean, western Pacific, and Australia to New Caledonia

The five remaining species of Nautilus and Allonautilus belong to a once numerous group of shelled cephalopods that existed from 400 to 65 million years ago. They are often referred to as “living fossils” because they are so

CLASS CEPHALOPODA

Giant Octopus Enteroctopus dofleini LENGTH

Up to 15 ft (4.5 m) HABITAT

Bottom dwellers, 30–2,500 ft (9–750 m)

DISTRIBUTION

Temperate northwest and northeast

Pacific

OCEAN LIFE

The giant octopus is one of the largest invertebrates as well as one of the most intelligent. It can solve problems, such as negotiating a maze

little changed from their ammonoid ancestors.Their shell protects them from predation, while gas trapped in its inner chambers provides buoyancy. The head protrudes from the shell and has up to 90 suckerless tentacles, which are used to capture prey such as shrimp and other crustaceans; the head also features a pair of rudimentary eyes that lack a lens and work on a principle similar to a pinhole camera.The nautilus swims using jet propulsion, drawing water into its mantle cavity and expelling it forcefully through a tubular siphon, which can be directed to propel the nautilus forward, backward, or sideways. Unlike most other cephalopods, nautiluses mature late, at about ten years of age, and produce only about twelve eggs per year. by trial and error, and remember the solution for a long time. It has large, complex eyes with color vision and sensitive suckers that can distinguish between objects by touch alone. It changes color rapidly by contracting or expanding pigmented areas in cells called chromatophores, enabling it to remain camouflaged regardless of background. It also uses its color to convey mood, becoming red if annoyed and pale if stressed. Most cephalopods show little parental care, but female giant octopuses guard their eggs for up to eight months until they hatch. They do not eat during that time, and siphon water over the eggs to keep them clean and aerated.

LENGTH

Up to 8 in (20 cm)

4–8 in (10–20 cm)

HABITAT

HABITAT

Deep water, to 6,500 ft (2,000 m)

Shallow water, rock pools

Northwest Atlantic

Little is known about the Dumbo octopus, as only a few have been recorded. Its common name derives from a pair of unusual, earlike flaps extending from the mantle above its eyes. It has a soft body, an adaptation to its deep-water habitat, and eight arms connected to each other almost to their tips by “webbing.” Its diet includes worms and snails.

Tropical west Pacific and Indian Ocean (all species of Hapalochlaena)

DISTRIBUTION

The most dangerous cephalopod is the small blue-ringed octopus, which produces highly toxic saliva powerful enough to kill a human. To catch prey, it either releases saliva into the water and waits for the poison to take effect, or catches, bites, and injects prey directly. Its bright coloring is unusual for an octopus, and the numerous blue rings covering its body become more iridescent if it is disturbed.

DEFENSE MECHANISM When threatened, a giant octopus squirts a cloud of purple ink out through its siphon into the water and at the same time moves backward rapidly using jet propulsion. Potential predators are left confused and disoriented in a cloud of ink. The octopus can repeat this process several times in quick succession.

A QUICK GETAWAY

This giant octopus is making a rapid retreat, expelling an ink jet as a defense mechanism. The jet also propels the octopus backward forcefully.

MOLLUSKS

289

CLASS CEPHALOPODA

Australian Giant Cuttlefish Sepia apama LENGTH

Up to 5 ft (1.5 m) HABITAT

Shallow water over reefs

DISTRIBUTION

Coastal Australian waters

Of about 100 cuttlefish species, the Australian giant cuttlefish is the largest. Like all cuttlefish, it has a flattened body and an internal shell, known as the cuttle and familiar to many as budgerigar food. This species lives for up to three years and gathers in huge numbers to breed. Males have elaborate courtship displays, which involve hovering in the water while making rapid, kaleidoscopic changes of color, as the male shown here is doing. When a female is receptive, the male deposits a sperm package in a pouch under her mouth. This later bursts, releasing sperm and fertilizing her 200 or more golf-ball-sized eggs, which she then deposits on a hard substrate. The eggs hatch into miniature adults after several months.

CLASS CEPHALOPODA

CLASS CEPHALOPODA

Common Squid

Glass Squid

Loligo vulgaris

Teuthowenia pellucida

DISTRIBUTION

Vampire Squid

LENGTH

LENGTH

Up to 12 in (30 cm)

1/ –11/ in 2 2

HABITAT

HABITAT

60–800 ft (20–250 m)

Midwater

Eastern Atlantic, Mediterranean

DISTRIBUTION

CLASS CEPHALOPODA

Vampyroteuthis infernalis LENGTH

Circumglobal in southern temperate

waters

A tubular body and a small, rodlike internal skeleton are characteristic features of all species of squid. They also have very large eyes relative to body size. The common squid is an inshore, commercially important species that has been harvested for centuries and is probably the best known of all cephalopods. It is a fast swimmer that actively hunts its prey, such as crustaceans and small fish. Once caught, the squid passes the prey to its mouth, where it is dismembered by powerful, beaklike jaws.

Up to 15 in (38 cm)

(1.4–3.8 cm)

Like many mollusks, juvenile glass squid live in the plankton, then descend to deeper, darker levels as they mature. The presence of light organs, called photophores, in the tips of their arms and in the eye may help in locating a mate. Sexually mature females are also thought to produce a chemical attractant, or pheromone.

HABITAT

1,600–5,000 ft (500–1,500 m), oxygen-poor water DISTRIBUTION

Tropical and temperate oceans

worldwide

CLASS POLYPLACOPHORA

Lined Chiton Tonicella lineata LENGTH

11/2 in (3.5 cm) HABITAT

Intertidal and subtidal zones, common on rocky surfaces DISTRIBUTION Temperate waters of northeast and northwest Pacific

coralline algae. The lined chiton’s mantle extends around the shell on all sides, forming an unusually smooth, leathery “girdle” that helps to hold its eight shell-plates together. It has a large, muscular foot, which it uses to move over rocks and, when still, to grip on to them in much the same way as limpets do. At low tide, it remains stationary to avoid water loss. Its head is small and eyeless. The sexes are separate and it reproduces by releasing its gametes into the water.

OCEAN LIFE

Chitons are mollusks with shells made up of eight arching and overlapping plates. The lined chiton is so called because of a series of zigzagging blue or red lines on its shell. The shell is usually pinkish in color, which provides good camouflage as this chiton grazes from rocks that are covered with encrusting pink

This is the only squid that spends its entire life in deep, oxygen-poor water. Like many deep-living creatures, the vampire squid is bioluminescent and has light organs, or photophores, on the tips of its arms and at the base of its fins. If threatened, it flashes these lights and writhes around in the water, finally ejecting mucus that sparkles with blue luminescent light. When the lights go out, the vampire squid will have vanished. Its predators include deep-diving whales.

290

ANIMAL LIFE

Arthropods THE ANIMALS THAT HAVE ACHIEVED

the greatest diversity on Earth are the arthropods, of which insects are by far the most KINGDOM Animalia numerous. However, most marine arthropods are crustaceans, PHYLUM Arthropoda such as crabs, shrimp, and barnacles. Crustaceans, including SUBPHYLA 4 both adults and larval stages, form most of the ocean’s SPECIES About 1.25 million zooplankton—the community of tiny, drifting life forms that support all oceanic food chains. Like land arthropods, all marine forms have an external skeleton, segmented body, and jointed appendages, permitting some, such as robber crabs, to live on land as well as in water. Fully marine insects are rare but some live on seashores and coasts. DOMAIN Eucarya

APPENDAGES

Anatomy

SEASHORE INSECTS

Springtails are wingless relatives of true insects. Marine species can be found in the upper regions of seashores and will spring into the air if disturbed. digestive gland

heart

This spotted cleaner shrimp has jointed walking appendages. Two furthers pairs of jointed appendages, which are located on its head, are modified into sensory antennae.

Although arthropods may look very different from one another, they all have an external skeleton (exoskeleton), which is either thin and flexible or rigid and toughened by deposits of calcium carbonate. The body is segmented and has a variable number of jointed appendages—some are used for walking and swimming, while others are modified into claws and antennae or adapted for feeding. Muscles are attached across the joints to facilitate movement. Most of the body cavity is hollow; this space, called the hemocoel, contains the internal organs and a fluid—hemolymph—that is the equivalent to vertebrate blood, which is pumped around the body by the heart in an open circulatory system. Most marine forms use gills for respiration and have well-developed sense organs. sensory antenna

stomach

merus

SPIDER FEATURES

Although it is called a crab and has a hinged carapace, this horseshoe crab is a close relative of spiders, ticks, and mites. Like them, it has piercing mouthparts.

dactylus

carpus eye

propodus

claw ischium coxa basis

swimmeret tail fan (telson)

nerve cluster (ganglion)

forward and backward movement

point of attachment to body

movements up and down

ARTHROPOD ANATOMY

ARTHROPOD LIMB

Lobsters have a protective shell carapace covering the head and thorax, large pincers, and well-developed walking appendages. The hemocoel contains the internal organs.

Walking appendages, such as this crab’s leg, comprise rigid sections linked with movable joints. The joints move in different planes, allowing versatile movement.

FILTER-FEEDING LIMBS

At high tide, barnacles feed by extending their long, feathery appendages from their “shell” and sweeping the water for plankton and detritus.

OCEAN LIFE

walking appendage

SCAVENGING IN THE SAND

As the tide retreats, this sand bubbler crab emerges to feed on the organic material contained in the sand.

Feeding Among crustaceans, feeding is extremely varied. Many crabs are scavengers that feed on dead and decaying organic matter. They are therefore vital in helping to recycle nutrients. Others are hunters and have robust claws to stun (mantis shrimp) or crush (lobsters) their prey before tearing it apart and consuming it. Many small planktonic crustaceans, such as copepods, are filter feeders that make effective use of various appendages, including long antennae, to create water currents that waft food particles toward their mouths. Barnacles, which are attached to rocks and unable to move, feed in a similar way, using their limbs to collect plankton. A few crustaceans are parasitic (some isopods, copepods, and the barnacle Sacculina) and obtain all their nourishment from their host. The shoreline is an ideal place for insects, such as kelp flies, that feed by releasing enzymes onto rotting seaweed and then taking in the resultant digested material. Farther inland, among the dunes, there is more vegetation, so spiders and pollen- and nectar-feeding insects start to appear.

HARD SKELETON AND JOINTED LIMBS

These tiny porcelain crabs, less than 1 in (2.5 cm) wide, are filter feeders. They have typical arthropod features, such as a hard exoskeleton covering a segmented body, and jointed limbs.

ARTHROPODS

Growth

291

HUMAN IMPACT

KRILL DECLINE

Crustaceans can only develop and grow by molting and replacing their exoskeleton with a larger one. The moulting process, called ecdysis, is controlled by hormones and occurs repeatedly during adult life. The exoskeleton is produced from the layer of cells situated immediately below it. Before a molt starts, the exoskeleton detaches from this cell layer and the space in between fills with molting fluid. Enzymes within this fluid weaken the exoskeleton so that it eventually splits at the weakest point, often somewhere along the back. The new exoskeleton is soft and wrinkled, so it needs to expand and then harden. Marine arthropods absorb water rapidly after molting to expand their new protective covering. Those that can remain hidden for hours or days, as they are more vulnerable to predation until their exoskeleton hardens.

Antarctic krill are only 21⁄2 in (6 cm) long but are among the most abundant crustacean arthropods. Numbers in the Southern Ocean have fallen over the past few decades, partly due to rising water temperatures and melting of ice. Krill feed on algae that grow beneath and within the sea ice, and shelter under the ice to avoid predation. Over-harvesting of krill for human and animal feed also poses a significant threat with potential to disrupt the Antarctic food web (see p.295).

THE MOLTING SEQUENCE

This sequence shows a harlequin shrimp molting. The exoskeleton has split just behind the neck joint, allowing the shrimp to pull out its head. The rest of its body quickly follows as the split enlarges. It takes only a few minutes for the shrimp to free itself completely, after which it rests for a few seconds. The new exoskeleton is soft, since it must be flexible to buckle up to fit inside the older, smaller skeleton. It stretches to accommodate the increased size of the shrimp. Complete hardening of the new exoskeleton will take about two days.

The old exoskeleton splits along the back behind the harlequin shrimp’s head. It eases out backward.

1

The shrimp emerges further and struggles to free itself from the old exoskeleton.

2

Molting is complete, and the old exoskeleton lies beside the shrimp, as the animal rests.

3

OCEAN LIFE

292

Lifestyles

PARASITISM

SEA SPIDERS As a group, sea spiders are typical of many problematic organisms whose classification is changing as information becomes available. In line with current thinking, they form a class (pycnogonids) within the subphylum that also contains spiders and horseshoe crabs (chelicerates). However, continuing research indicates they may form a completely separate group of arthropods. DECEPTIVE APPEARANCE

Sea spiders are so called because of their resemblance to land spiders, but their exact relationship to spiders is still not clear.

Some arthropods live closely with other species. This fish is being parasitized by an isopod, which is related to woodlice. There are two isopods, one under each eye, feeding on tissue fluid to the detriment of the fish.

All marine arthropods are freeliving for at least part of their lives. Some, such as crabs, have planktonic larvae that sink to the sea floor and become bottomliving, or benthic, as they mature. Crabs and their relatives tend to live alone unless seeking a partner to breed with, and may defend COMMENSALISM territory. Others, such as This crab is camouflaged by a sea squirt in krill and copepods, live in a commensal relationship. The crab benefits but the sea squirt neither gains nor loses. vast swarms, traveling hundreds of yards up and down the water column each day to feed (see p.221). Adult barnacles remain anchored to one spot (that is, they are sessile), often settling in large aggregations on rocky shores where living conditions are most favorable. Deep-sea arthropod species are not well known, but many have cryptic red or black coloration to make themselves invisible, while others such as krill, have light organs and exhibit bioluminescence. A few arthropods live in close association with other species. Sometimes both partners benefit from a relationship (mutualism), sometimes only one has an advantage (commensalism), and sometimes one gains at some cost to the other (parasitism).

Reproduction and Life Cycles

egg mass on underside of female crab

In most crustaceans, the sexes are separate, fertilization is often internal, and the eggs must be laid in water. Some females store sperm and then let it flow over their eggs as they release them. Others protect their eggs by carrying them around, and keep them healthy by continually wafting water over them. On hatching, the larvae join the zooplankton, and pass through various stages before maturing into adults. Barnacles are both male and female (hermaphroditic) but only function as one sex at a time. The male has a long, extendable penis and mates with all neighboring females within reach. In horseshoe crabs, fertilization occurs externally. Males and females pair up, the males fertilize the eggs as the females lay them in the sand, and then both sexes abandon them.

ARTHROPOD CLASSIFICATION Arthropods are split into four subphyla—Crustacea, Chelicerata, Hexapoda, and Myriapoda. All have marine species except for the non-marine Myriapoda (centipedes and millipedes, not described below). CRUSTACEANS Subphylum Crustacea

OCEAN LIFE

61,710 species

Crustaceans are the dominant marine arthropod group and include the familiar crabs, lobsters, shrimps, prawns, and barnacles as well as the smaller copepods, isopods, and krill. Most crustaceans have two pairs of antennae and three body segments, the head and the thorax (often fused together as the cephalothorax) and the abdomen. The head and thorax are often protected by a shield, or carapace. Paired appendages vary

greatly—some are sensory, while others are adapted for walking or swimming; sometimes there is also a large pair of claws. CHELICERATES Subphylum Chelicerata 71,004 species

Spiders, scorpions, ticks, mites, horseshoe, crabs, and sea spiders belong to this group. A few species of spiders live in the intertidal zone, and some types of ticks and mites are either free-living or parasitic in marine habitats. The horseshoe crabs (class Merostomata) are completely marine. They have five pairs of

legs and their body comprises two parts, called the prosoma and opisthosoma. In horseshoe crabs, the prosoma contains most of the body organs, and the opisthosoma has most of the musculature and the book gills, which are used for respiration. What makes this group unique among chelicerates is the hinged carapace that protects the body and the long, tail-like telson, which the crab uses to right itself if it is accidentally inverted. Sea spiders (class Pycnogonida) are all marine. They are spiderlike, and most have a leg span of less than 1 in (2.5 cm). Many species have a unique pair of appendages, called ovigers, overhanging the head. The females use them for grooming, courtship, and also to transfer eggs to the ovigers of the male, where they remain until they hatch. Sea spiders are common in intertidal areas, but they are rarely seen due to their small size.

CRAB MOTHER AND LARVA

A velvet crab (above) carries eggs beneath her body until they hatch. The hatchlings enter a planktonic larval stage called a zoea (left). This molts four to seven times before it becomes a megalops larva, then once again to become an adult crab.

HEXAPODS Subphylum Hexapoda 1.11 million species

By far the largest group within the Hexapoda is the insects—the largest of all animal groups. It includes beetles, flies, ants, and bees. Most insects have compound eyes and three distinct body segments—the head, the thorax with its three pairs of walking appendages, and the abdomen. Many species also have wings. Many insects live in coastal areas, but only a few live on the shore. Only one type of insect is truly marine—the marine skater, Halobates, a type of “true bug” (order Hemiptera). Of the 40 coastal species, only five are able to spend their entire life on the ocean. However, they require a solid object, such as a floating feather or lump of tar, on which to lay their eggs.

ARTHROPODS SUBPHYLUM CHELICERATA

SUBPHYLUM CHELICERATA

Giant Sea Spider

American Horseshoe Crab

Colossendeis australis 10 in ( 25 cm) (leg-span)

LENGTH

WEIGHT

Not recorded

HABITAT

Bottom

Limulus polyphemus LENGTH

Up to 24 in

(60 cm) WEIGHT

dweller

Up to 11 lb (5 kg)

Sandy or muddy bays to 100 ft (30 m) HABITAT

DISTRIBUTION

Antarctic shelf and slope

Unlike most sea spiders, which have a leg-span of less than 1 in (2.5 cm), the giant sea spider has a huge leg-span of about 10 in (25 cm). It has a large proboscis through which it sucks its food, but its body is so small that the sex organs and parts of its digestive system are situated in the tops of the legs. Sea spiders are somewhat unusual among arthropods in that some exhibit parental care, the males having a modified pair of legs to carry the eggs until they hatch.

Western Atlantic and Gulf Coast from southern Maine to the Yucatán Peninsula

DISTRIBUTION

Despite its name, the American horseshoe crab is more closely related to spiders than to crabs. It is mainly active at night and scavenges anything it can find, including small worms, bivalves, and algae. Its horseshoeshaped, greenish-brown outer shell, or carapace, is for protection, and adults have few predators. It has six pairs of thoracic appendages: the first pair (called chelicerae), is used for feeding;

the other five are for walking and for grasping and tearing food. Five pairs of flattened abdominal appendages are used for swimming and scuttling along the bottom and also carry pagelike “book gills,” through which oxygen is absorbed. Its long, rigid tail is used for steering and for righting itself. Hinged to the body, it can act as a lever. The reproductive cycle is closely linked to spring high tides, when adults gather in large numbers on sandy beaches to breed. Females lay up to 80,000 eggs in a depression near the high-tide mark, providing a vital food source for birds and other marine creatures. The eggs are laid in batches mostly when the moon is in its full or new phases. The eggs hatch into tailless “trilobite larvae,” so called because they look a bit like fossil trilobites. Carried down the shore at high tide, the larvae swim around actively but also burrow into the sediment for safety. After a few days, they molt and become juveniles.

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HUMAN IMPACT

MEDICAL RESEARCH If the American Horseshoe Crab is injured, some of its blood cells form a clot, which kills harmful negative bacteria. In order to exploit this property for human benefit, crabs are collected from shallow waters on the Atlantic coast of North America during the summer months. Researchers then remove about 20 percent of the blood from each crab. From this they extract a protein that is used to detect bacterial contamination in drugs and medical devices that will be in contact with blood. Taking blood from the crabs is sometimes fatal to them but most recover after they have been returned to the sea.

SUBPHYLUM CRUSTACEA

Water Flea Evadne nordmanni LENGTH 1/32 in WEIGHT

(1 mm)

Not recorded

Open waters, to depths of 6,500 ft (2,000 m)

HABITAT

DISTRIBUTION

Temperate and cool waters worldwide

Most water fleas live in freshwater but this species and just a few others live as plankton in the ocean. It feeds on tiny bacteria, protists, and organic debris and is eaten by larger planktonic animals. It has a single conspicuous eye and feathery swimming appendages that are modified antennae. Females brood unfertilised eggs that hatch into more females. Sexual reproduction also occurs. large eye

OCEAN LIFE

feathery swimming appendage

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ANIMAL LIFE SUBPHYLUM CRUSTACEA

Cyclopoid Copepod

Gooseneck Barnacle

Oithona similis

Pollicipes polymerus LENGTH 1/ –3/ in 54 32

LENGTH

(0.5–2.5 mm)

Up to 3 in (8 cm)

HABITAT

HABITAT

Surface waters to a depth of 500 ft (150 m)

Intertidal zone of rocky shores

DISTRIBUTION Atlantic, Mediterranean, Southern Ocean, southern Indian and Pacific oceans

DISTRIBUTION Eastern Pacific coast of North America, from Canada to Baja California, Mexico

Copepods make up a large percentage of zooplankton, and this is one of the most abundant, widespread species. As the name suggests, cyclopoid copepods have a single, central eye, which is light sensitive. They have a tiny, oval body that tapers to a thin tail. Most have six body segments and six pairs of swimming limbs. Tiny food particles are filtered from the water using specialised mouthparts. Females can be recognized when carrying egg sacs attached to their abdomens. As part of the zooplankton, copepods of this genus are a vital element of oceanic food chains. They feed on marine algae and bacteria and in turn are an important source of protein for many ocean-dwelling animals. Every night cyclopoid copepods migrate from a depth of about 500 ft (150 m) to the surface layers of the ocean to feed. This daily journey, which is undertaken by many marine creatures, is one of the largest mass movements of animals on Earth.

So called because of its resemblance to a goose neck and head, the gooseneck barnacle forms dense colonies in crevices on rocky shores with strong waves. Barnacles anchor themselves to rocks by a tough, flexible stalk (peduncle), which also contains the gonads. This is actually their “head” end. Once the barnacle has attached itself to an object it secretes a series of pale plates at the end of its stalk, forming a shell around its featherlike legs, which comb through the water for food. The legs face away from the sea, enabling the barnacle to feed by filtering out particles of detritus from returning tidal water as it funnels past them through cracks in the rocks. These barnacles become sexually mature at about five years of age and may live for up to 20 years. The larval stage is free-living but depends on sea currents for its transport and survival. Colonies of gooseneck barnacle are susceptible to the damaging effects of oil pollution and they recover only slowly from disturbance.

SUBPHYLUM CRUSTACEA

Acorn Barnacle Semibalanus balanoides LENGTH

Up to 1/2 in (1.5 cm) diameter HABITAT

Intertidal zone of rocky shores DISTRIBUTION Northwest and northeast Atlantic, Pacific coast of North America

OCEAN LIFE

SUBPHYLUM CRUSTACEA

Like all adult barnacles, the adult acorn barnacle remains fixed in one place once it has anchored itself to a site. The free-swimming juveniles pass through several larval stages before molting into a form that can detect both other acorn barnacles and suitable anchoring sites. Once a larva fixes itself to a rock, using cement produced by glands in its antennae, it molts again. It then secretes six gray calcareous plates, forming a protective cone that looks rather like a miniature volcano. Four smaller, movable plates

at the top of the cone open, allowing the acorn barnacle to feed. It does this when the tide is in by waving its modified legs, called cirri, in the water to filter out food. When the tide is out, the plates are closed to prevent the barnacle from drying out. Acorn barnacles are hermaphrodites that possess both male and female sexual organs, but they function as either a male or a female. They do not shed their eggs and sperm into the water; instead they use extendable penises, to transfer sperm to receptive neighbors.

PEOPLE

CHARLES DARWIN Before the British naturalist Charles Darwin (1809–1882) proposed his revolutionary theory of evolution in The Origin of Species (1859), he spent eight years studying barnacles. Realizing the impact his ideas on evolution would have on existing scientific and religious thinking, he delayed writing and instead produced four monographs on the classification and biology of barnacles. This work earned him the Royal Society’s Royal Medal in 1853, validating his reputation as a biologist.

ARTHROPODS SUBPHYLUM CRUSTACEA

Giant Mussel Shrimp Gigantocypris muelleri LENGTH 1/ –3/ in 2 4

(1.4–1.8 cm)

SUBPHYLUM CRUSTACEA

Peacock Mantis Shrimp Odontodactylus scyallarus LENGTH

HABITAT

Up to 6 in (15 cm)

Planktonic, intermediate to deep sea

DISTRIBUTION

HABITAT

Warm water near reefs with sandy, gravelly, or shelly bottoms

Atlantic, Southern Ocean, western

Indian Ocean DISTRIBUTION

Indian and Pacific oceans

Like all ostracod crustaceans, the giant mussel shrimp has a carapace that encloses its body, so that its seven pairs of limbs are almost hidden from view. Its large, mirror eyes with parabolicshaped reflectors focus light on to a flat plate in its center. It is planktonic, but lives at greater depth than many forms of plankton, usually below 650 ft (200 m), where it feeds on falling detritus. The picture shows a large female carrying embryos, which are clearly visible through the carapace.

SUBPHYLUM CRUSTACEA

Sea Slater Ligia oceanica LENGTH

Up to 11/4 in (3 cm) HABITAT

Coasts with rocky substrata

DISTRIBUTION

Atlantic coasts of northwestern

Europe

Commonly found under stones and in rock crevices, the sea slater is a seashore-dwelling a member of the isopods (a group that also includes woodlice). It lives in the splash zone, but can survive periods of immersion in salt water. Its head, which has a pair of well-developed compound eyes and very long antennae, is

SUBPHYLUM CRUSTACEA

Sand Hopper Orchestia gammarellus 1/16 –3/8 in

(2–10 mm)

HABITAT

Splash zone of sandy shores DISTRIBUTION Atlantic coasts of northeastern Canada and northwestern Europe

uropod

SUBPHYLUM CRUSTACEA

Antarctic Krill Euphausia superba LENGTH

Up to 2 in (5 cm) HABITAT

Planktonic

DISTRIBUTION

Southern Ocean

All oceans contain krill—small, shrimplike, planktonic crustaceans that live in open waters. Antarctic krill live in vast numbers in the subantarctic waters of the Southern

Such power is created by a special, saddlelike hinge-joint in these legs, which acts like a spring. The peacock mantis shrimp can smash the shells of gastropods and crabs and tackles prey larger than itself. It excavates U-shaped burrows or lives in crevices in rocks or coral. After hatching, its larvae enter the plankton, where they develop over a few weeks before drifting down toward the sea floor to make their own homes.

Ocean, where they form a vital link in the food chain, being eaten in vast quantities by baleen whales, seals, and various fish. Krill rise to the surface at night to feed on phytoplankton, algae, and diatoms. For safety they sink to greater depths during the day. The feathery appearance of this species is due to its gills, which, unusually, are carried outside the carapace. Their filamentous structure increases the surface area available for gaseous exchange. Antarctic krill also have large light organs, called photophores. The light is thought to help them group together. They spawn in spring, during which females may release several broods of up to 8,000 eggs.

antenna

Amphipod crustaceans, such as the sand hopper, live in large numbers in the splash zone of any shore where there is rotting seaweed. Their life cycle takes about 12 months and the female usually produces only one clutch of eggs, which she keeps in a brood pouch, where they hatch after one to three weeks. The young leave the pouch about a week later when their mother molts. Sand hoppers are also known as sand fleas because they jump about in a similar way and have similar laterally compressed bodies.

OCEAN LIFE

LENGTH

not markedly separated from its body, which is flattened, about twice as long as it is broad, and ends in two forked projections called uropods. As adults, sea slaters have six pairs of walking legs until their final molt, after which they have seven. The sea slater is not generally seen during the day unless it is disturbed, and it emerges from its hiding place only at night to feed on detritus and decaying seaweed. Sea slaters mature at about two years of age and usually breed only once before dying.

The brightly colored peacock mantis shrimp is a stomatopod crustacean. Like all members of this group, it is a voracious predator. Its large, mobile, compound eyes have sophisticated stereoscopic and color vision that includes some ultraviolet shades. It uses sight when hunting, waiting quietly, like the praying mantis, for its unsuspecting prey to come within reach, then striking using its powerful, clublike second pair of legs with immense speed—about 75 mph (120 km/h)—and force (up 100 times its own weight).

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296

ANIMAL LIFE SUBPHYLUM CRUSTACEA

SUBPHYLUM CRUSTACEA

Deep Sea Red Prawn

Common Prawn

Acanthephyra pelagica

Palaemon serratus

LENGTH

DISTRIBUTION

41/4 in

Up to

HABITAT

HABITAT

Atlantic

In the low light levels of the deep ocean, red appears black, making the deep sea red prawn invisible to potential predators. Its hard outer casing, or exoskeleton, is thinner and more flexible than that of shallowwater crustaceans, which helps prevent them from sinking into the depths. The flesh of this prawn is also oily to aid further buoyancy. It uses its first three pairs of limbs to feed on small copepods. The remaining five pairs of limbs, the pereiopods, are used for locomotion. Gills attached to the tops of the legs are used for respiration.

PRAWN FARMING

LENGTH

Not recorded Deep water

HUMAN IMPACT

(11 cm)

Rock pools, shallow water, and lower parts of estuaries DISTRIBUTION Eastern Atlantic from Denmark to Mauritania, Mediterranean, Black Sea

The common prawn has a semitransparent body, making its internal organs visible, and is marked with darker bands and spots of brownish red. As with many other species of prawn, its shell extends forward between its stalked eyes to form a stiff, slightly upturned projection called a rostrum. This feature has a unique structure by which the common prawn can be distinguished from all other members of the same genus. The rostrum curves upward, splitting in two at the tip, where it has several toothlike projections on the lower and upper surfaces. To either side of the rostrum there is a very long antenna that can sense any danger close by and is also used to detect food. Of the prawn’s five pairs of legs, the rear three pairs are used for walking, while the front two pairs are pincered and used for eating. Attached to the abdomen is a series of smaller limbs called swimmerets that the

Nearly all the world’s farmed prawns come from developing countries such as Thailand, China, Brazil, Bangladesh, and Ecuador, which use intensive farming to meet demand. Cutting mangrove forests to construct prawn ponds is now being discouraged. SHARED RESOURCES

Fishermen in Honduras fish for wild prawns in a lagoon shared with prawn farmers.

prawn uses to swim. For a sudden, backward movement, the prawn flicks its tail. Females produce and look after about 4,000 eggs until they hatch into larvae. The larvae float among the plankton until they mature. pincered leg

tail fan, or telson

SUBPHYLUM CRUSTACEA

Anemone Shrimp Periclimenes brevicarpalis LENGTH

1 in (2.5 cm) HABITAT

Shallow water reefs

OCEAN LIFE

DISTRIBUTION

Indian Ocean, western Pacific

Nestling among the tentacles of an anemone, the anemone shrimp is safe from attack by predators. It rarely wanders far from its host, surviving by scavenging scraps that the anemone cannot eat. The shrimp may benefit the anemone by removing excess food particles as well as any waste it produces. This type of relationship is called commensalism: one individual in the partnership profits from the liaison and the other comes to no harm. Removed from its host, this shrimp is defenseless. The anemone shrimp belongs to the same family (Palaeomonidae) as the common prawn (above) and so they have several features in common. These include a pair of long, sensory antennae used to sense danger and detect food and a rostrum (the elongated projection of the shell from between the eyes). The anemone shrimp is almost completely transparent, with a few purple and white spots.

ARTHROPODS SUBPHYLUM CRUSTACEA

SUBPHYLUM CRUSTACEA

Spiny Lobster

European Lobster

Panulirus argus

Homarus gammarus LENGTH

LENGTH

24 in (60 cm)

Up to 3 ft (1 m), typically 24 in (60 cm)

HABITAT

Coral reefs and rocky areas

DISTRIBUTION

HABITAT

Rocky coasts

Western Atlantic, Gulf of Mexico,

DISTRIBUTION Eastern Atlantic, North Sea, Mediterranean

Caribbean Sea

Being both nocturnal and migratory, the spiny lobster has excellent navigational skills. It can establish its position in relation to Earth’s magnetic field and then follow a particular route as well as any homing pigeon. This lobster prefers warm

SUBPHYLUM CRUSTACEA

Reef Hermit Crab Dardanus megistos WIDTH (LEG-SPAN)

Up to 12 in (30 cm) HABITAT

Near-shore tropical reefs

DISTRIBUTION

Indian and Pacific oceans

Like other hermit crabs, the reef hermit crab uses an empty gastropod mollusc shell to protect its soft abdomen. When it grows too big for its current shell, it simply looks for an unused larger one or evicts a weaker rival. It is while switching from one

SUBPHYLUM CRUSTACEA

Robber Crab Birgus latro LENGTH

Up to 24 in (60 cm) across HABITAT

Rock crevices and sandy burrows

DISTRIBUTION

oceans

Tropical waters of Indian and Pacific

water and so remains in the shallows in summer before migrating in groups to deeper water in winter by walking in single file across the sea floor. It lacks the large claws of the European lobster (right) but is well protected from most predators by the sharp spines that cover its carapace. shell to the next that the reef hermit crab is most vulnerable, as it risks exposing its soft, rather asymmetrical abdomen to predators. There are about 1,150 species of hermit crabs — the reef hermit crab lives in shallow-water tropical reef habitats, but some species live on coastal land. The reef hermit crab is a scavenger rather than a hunter, and drags itself over the seafloor looking for bits of animal matter and algae, tearing apart any carcasses that it finds with its dextrous mouthparts. Its close relative Dardanus pedunculatus attaches stinging anemones to its shell as rotection from predators. The robber crab, or coconut crab, is the largest terrestrial arthropod. Like its close relatives other hermit crabs, it lives inside a mollusk shell when young but discards this as it grows bigger and tougher. It lives on oceanic islands and offshore inlets. It mainly eats fruit and nuts but will also scavenge for carrion. It can smash and eat coconuts but rarely does so. Adults live and mate on land, but females release their eggs into water.

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In life the European lobster is brown or bluish—it only turns the familiar red when it is cooked. Individuals weigh up to 11 lb (5 kg). It has large, differently sized claws: the smaller one has sharper edges and is used for cutting prey, while the larger one is used for crushing. The European lobster lives in holes and crevices on the sea bed. The European lobster is commercially important and in danger of overexploitation because it matures slowly, and is such a valuable commodity.

crushing claw cutting claw

eye stalk

SUBPHYLUM CRUSTACEA

Porcelain Crab single large claw

Petrolisthes lamarckii WIDTH (SHELL)

Up to 3/4 in (2 cm) HABITAT

Pools on rocky beaches and shorelines DISTRIBUTION Indian Ocean, Pacific coast of Australia, western Pacific

SUBPHYLUM CRUSTACEA

The flat, rounded body of the porcelain crab allows it to slip easily into small rock crevices to hide. However, if it becomes trapped by a predator or stuck beneath a rock, it can shed one of its claws in order to escape, and a new one will grow over time. This crab’s abdomen is folded under its body, but it can be unfolded and moved like a paddle when swimming.

Nodose Box Crab Cyclozodion angustum LENGTH

Not recorded HABITAT

Offshore to depths of 50–650 ft (15–200 m)

DISTRIBUTION

Western Atlantic, Gulf of Mexico,

Caribbean Sea

Previously known as Calappa angusta, the nodose box crab is a true crab with a small abdomen that is tucked away underneath the body and four pairs of legs. This species may be recognized by the rows of nodules that radiate from behind its eyes across the upper surface of its yellowish shell, or carapace.

SUBPHYLUM CRUSTACEA

Japanese Spider Crab Macrocheira kaempferi WIDTH (SHELL)

Up to

141/2 in (37 cm) Deep-water vents and holes to depths of 160–1,000 ft (50–300 m)

HABITAT

DISTRIBUTION

Pacific Ocean near Japan

OCEAN LIFE

Not only is the giant Japanese spider crab the largest of all crabs, with a leg-span of up to 13 ft (4 m) and weighing 35–44 lb (16–20 kg), it may also be the longest living, estimated to live for up to 100 years. Living in the deep, cold waters around Japan, it moves slowly across the ocean floor on its spiderlike legs, scavenging for food.

PORCELAIN CRAB

The porcelain crab uses its flat body to crawl out of reach of predators. Here, the tentacles of an anemone provide a secure and permanent home for a porcelain crab in the Andaman Sea in the northern Indian Ocean. The mouthparts of the crab fan out and trap plankton, which it then brushes into its mouth.

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ANIMAL LIFE SUBPHYLUM CRUSTACEA

Long-legged Spider Crab Macropodia rostrata LENGTH

Up to 1 in (2.5 cm) HABITAT

Lower shore, usually not beyond 165 ft (50 m) Northeastern Atlantic from southern Norway to Morocco, Mediterranean DISTRIBUTION

Also called the decorator crab because it camouflages itself using fragments of seaweed and sponges, the longlegged spider crab is covered in

SUBPHYLUM CRUSTACEA

hook-shaped hairs that hold its disguise in place, enabling it to blend in with the seaweed among which it lives. This crab has a triangular-shaped carapace that extends forward between the eyes into an eighttoothed projection called a rostrum. Its spiderlike legs are at least twice as long as its body and can be used, somewhat ineffectively, for swimming. The long-legged spider crab feeds on small shellfish, algae, small worms, and detritus. Breeding occurs year-round on Atlantic coasts, but takes place between March and September in the Mediterranean. The male transfers sperm to the female using its first pair of abdominal legs. The female carries the eggs until they hatch into larvae that live in the plankton.

SUBPHYLUM CRUSTACEA

Edible Crab

Pea Crab

Cancer pagurus

Pinnotheres pisum LENGTH

LENGTH

Up to 6 in (16 cm)

Males 1/3 in (8 mm); females 1/2 in (14 mm)

HABITAT

Intertidal zone to 330 ft (100 m), in rock pools and muddy sand offshore

SUBPHYLUM CRUSTACEA

Spotted Reef Crab Carpilius maculatus LENGTH

About 31/2 in (9 cm) HABITAT

Shoreline to 33 ft (10 m), inshore reefs

DISTRIBUTION

SUBPHYLUM CRUSTACEA

Common Shore Crab Carcinus maenas LENGTH

Up to 21/2 in (6 cm)

HABITAT

Intertidal zone to 500 ft (150 m)

DISTRIBUTION Northeastern Atlantic and North Sea; introduced to parts of the Mediterranean

DISTRIBUTION Eastern Atlantic from northwestern Europe to West Africa, Mediterranean

The oval carapace of the edible crab has a characteristically “scalloped” or “piecrust” edge around the front and sides. Its huge pincers are distinctively black-tipped, while the body is purple-brown in small individuals and reddish brown in larger ones. Edible crabs mate at different times in different parts of their range, the females incubating their eggs for six to nine months. This crab is caught in large numbers and is highly valued as a luxury food.

Typically about the size of a pea, the tiny pea crab is usually found inside the shells of the common mussel. Protected from predators in the mantle cavity of its host, it feeds on any plankton that becomes trapped on the mussel’s gills as water passes over them. Whether the presence of this guest is harmful to the mussel is unclear. Female pea crabs are substantially larger than males and have an almost translucent carapace through which their pink reproductive organs are visible. Males have harder, yellowish brown carapaces that protect them during the breeding season, which runs from April to October. During this time, males leave the safety of their host’s shell and swim around looking for females with which to mate. In regions where shellfish are harvested commercially, the pea crab is considered a pest.

HABITAT

Intertidal zone to 200 ft (60 m), all substrates; estuaries Northeastern Atlantic from Norway to West Africa; introduced elsewhere

DISTRIBUTION

black eye on short eye stalk

mouth

Indian Ocean and western Pacific

The conspicuous coloring of the spotted reef or coral crab is highly distinctive. Its smooth, light brown carapace has two large red spots behind each eye, three across the middle, and either two or four at the rear. Between the eyes the carapace has four small, rounded projections, which are also characteristic of the species. It is a nocturnal, slow-moving crab that uses its disproportionately large claws to feed on corals, snails, and other small marine creatures.

The common shore crab tolerates a wide range of salt concentrations and temperatures and so can live in salt marshes and estuaries as well as along the shoreline. Its dark green carapace has five marked serrations on the edge behind the eyes. This opportunistic hunter preys voraciously on many types of animals, including bivalve mollusks, polychaetes, jellyfish, and small crustaceans. Where introduced, it may be detrimental to local marine life. On the west coast of the US, for example, it has had a considerable impact on the shellfish industry.

ARTHROPODS SUBPHYLUM CRUSTACEA

Blue Swimming Crab Portunus pelagicus LENGTH

Up to 23/4 in (7 cm) HABITAT

Intertidal sandy or muddy sea beds to 180 ft (55 m) DISTRIBUTION Coastal waters of the Indian and Pacific oceans, eastern Mediterranean

SUBPHYLUM CRUSTACEA

Orange Fiddler Crab Uca vocans LENGTH

About 1 in (2.5 cm) HABITAT

Near water on mud or sand

DISTRIBUTION

Indian Ocean and western Pacific

Like its close relative the ghost crab (see above, right), the male orange fiddler crab also exhibits ritualistic displays to deter rivals. Males are easily recognized because one of their claws

Unlike most crabs, the blue swimming crab is an excellent swimmer and uses its fourth pair of flattened, paddlelike legs to propel itself through the water. Despite its common name, only the males are blue, and the females are a rather dingy greenish brown. Males also differ in having very long claws, more than twice as long as the width of their carapace. The claws are armed with sharp teeth that are used to snag small fish and other food items. When a blue swimming crab feels threatened, it usually buries itself in the sand. If this measure fails to deter the threat, the crab adopts its own threat stance, extending its claws sideways in an attempt to look as large as possible. The natural range of this crab has been extended to a small part of the eastern Mediterranean by the opening of the Suez Canal. It is a popular food in Australia. is greatly enlarged. In a mature adult this claw makes up more than half the crab’s body weight and is used both to attract potential mates and to ward off rival males. Observing the distinctive “courtship wave” of fiddler crabs is helpful in identifying different species. Orange fiddler crabs are active during the day. As well as digging a main burrow up to 12 in (30 cm) deep, they create a number of bolt holes into which they can retreat if danger threatens. At high tide, they seal themselves into their burrows with a small pocket of air. The presence of air is essential for their survival because fiddler crabs obtain oxygen from air, not water, despite having gills.

SUBPHYLUM CRUSTACEA

Ghost Crab Ocypode saratan LENGTH

About 11/2 in (3.5 cm) HABITAT

Sandy shores in deep burrows above the water line DISTRIBUTION Coastal waters of western Indian Ocean, Red Sea

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Resting in the cool of its burrow during the day, the fast-moving ghost crab emerges at twilight to hunt. It will eat anything it can find, including other crabs, and also scavenges whatever was brought in by the last tide. During the mating season, males defend their burrows, but they rarely fight, any disputes being settled by ritualistic displays. Their burrows can be over 330 ft (100 m) from the sea and over 3 ft (1 m) deep.

RITUAL DISPLAY Each species of fiddler crab waves its claw in a slightly different way. If this ritual movement does not deter a rival male, then two crabs may “arm-wrestle” each other to resolve their dispute. The weaker individual usually retreats before any serious damage is done. LEFT- OR RIGHT-HANDED?

Both crabs in this picture are righthanded, but in some males it is the left claw that is enlarged (see below).

OCEAN LIFE

RESTORING THE BALANCE

On arriving at the shore, the crabs head to the ocean, where they replace water and body salts lost during the arduous journey down from the forest plateau.

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Red Crab Migration TRAVELING ACROSS LAND

STAGES OF MIGRATION

RELEASING EGGS

The remarkable annual migration of the red crab (Gecarcoidea natalis) from the forests of Christmas Island (southwest of Indonesia) down to the sea to spawn is one of the wonders of the natural world. Until recently, about 120 million of the crabs made the journey each year, spending the rest of the time on a forested plateau about 1,200 ft (360 m) above sea level. Red crabs are mainly herbivorous, feeding on fallen leaves, fruit, and flowers gathered from the forest floor, but they also eat other dead crabs and birds when the opportunity arises. They conserve water by restricting their activity to times of high humidity (over 70 percent), retreating to their burrows during drier periods. Like their marine counterparts, red crabs have gills for respiration, but the gill chamber of this species is lined with tissue that acts as a lung and maximizes gaseous exchange. Red crabs on Christmas Island have undergone a noticeable decline in numbers, largely due to the accidental introduction of the yellow crazy ant in the 1930s. Since the mid-1990s, about 20 million red crabs are thought to have been killed by the ants, which squirt formic acid on the crabs as a defense mechanism when they are disturbed. There is also pressure to increase the number of phosphate mines on the island, which would involve deforestation, depriving the crab of its habitat in the affected areas.

MAN-MADE OBSTACLES Although the distance to the shore is only about 1,600 ft (500 m), red crabs have to negotiate a number of obstacles, including roads and hot train tracks. In the past, it was not unusual for one million crabs to perish each year, yet this had little impact on the population. Today, various measures such as road closures and concrete underpasses offer some security to the crabs, but they still run the risk of dying from dehydration during their journey. EGG RELEASE After incubating up to 100,000 eggs for 12–13 days, the females leave their burrows and gather on the shore to disperse them directly into the sea. They do so at night, as the high tide turns, by raising their claws and shaking their bodies vigorously to free the eggs from their pouches. Crabs on the cliffs may be 25 ft (8 m) above the water.

MEGALOPAE LARVAE Red crab eggs hatch as soon as they hit the water. The young remain in the ocean for up to 30 days, and pass through several larval stages before returning to the shallows as shrimplike megalop larvae. They metamorphose into tiny crabs after 3–5 days and leave the water to start life on land.

The onset of the wet season on Christmas Island, usually in early November, signals the start of the red crabs’ migration, which takes place over three lunar cycles. The males set off first, followed by females. It takes about a week for the crabs to reach the shore. After dipping in the ocean, the males compete fiercely for space to dig their burrows, where it is thought mating takes place. The males then return inland, leaving the females to brood their eggs in the burrows. They emerge after about two weeks to release their eggs into the sea at high tide at night during the last quarter of the moon. Phases of the moon over a 3-month period from November to January

full moon

FROM SEA TO LAND

The Sequence of Migration

new moon females and males males females

in early November, the crabs start to move down from forest plateau to the shore to breed

females return to the forest

in the second and largest migration, the crabs dip in the sea to replenish body salts, then the males fight to establish burrows

after mating, males dip a second time, then either return inland immediately or remain and feed

females move to the shoreline, releasing eggs into the sea at the turn of the high tide during the last quarter of the third lunar cycle

OCEAN LIFE

young crabs emerge after about a month, having matured in the water

first wave of crabs reaches the shoreline

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ANIMAL LIFE SUBPHYLUM HEXAPODA

SUBPHYLUM HEXAPODA

Shore Bristletail

Rock Springtail

Petrobius maritimus

Anurida maritima

DISTRIBUTION

LENGTH

LENGTH

2/ 5

Up to 1/8 in (3 mm)

in (1 cm)

HABITAT

HABITAT

Rocky shores in the splash zone

Upper intertidal zone of rocky shores

British Isles excluding Ireland

The Shore Bristletail, also known as the Sea Bristletail, derives its common name from the three long filaments extending from the tip of its abdomen. Its long body is wellcamouflaged by drab-colored scales. It has long antennae and compound eyes that meet at the top of its head. The shore bristletail lives in rock crevices and feeds on detritus. It can move swiftly around the rocks using small spikes on its underside, called styles, to help it grip. When disturbed, it can leap small distances through the air by using its abdomen to catapult it away from the rock.

DISTRIBUTION

Coasts of the British Isles

At low tide hundreds of rock springtails wander down the beach searching for food, returning to the shelter of their rock crevices an hour before the tide turns.Vast numbers

in (1 cm)

HABITAT

Sand dune systems

Marine Skater

Kelp Fly

Halobates sericeus

Coelopa frigida

LENGTH

LENGTH

Females: 1/5 in (5 mm)

1/ –2/ 8 5

HABITAT

HABITAT

Ocean surface

Temperate shores with rotting seaweed

OCEAN LIFE

DISTRIBUTION Pacific Ocean between 40º and 5º north and south of the equator

This is a member of the only truly marine genus of insects. The marine skater spends its entire life on the surface of tropical and subtropical oceans where winter temperatures rarely fall below 68ºF (20ºC). Little is known about these insects due to the difficulty in studying them. Females are larger than males and after mating they lay 10–20 cream-colored, oval eggs on a piece of flotsam, such as a piece of floating wood. The eggs hatch into nymphs that molt through five stages before becoming adults. Because this insect never dives below the surface, its diet is restricted to small organisms such as floating fish eggs, zooplankton, and dead jellyfish. It feeds by releasing enzymes onto the surface of its food and then drawing in the predigested material through its modified mouthparts.

DISTRIBUTION

shorelines

in (3–10 mm)

North Atlantic and north Pacific

LENGTH

Up to 3/4 in (2 cm) HABITAT

Intertidal sandy and muddy shores Coasts of the British Isles and northern Europe

DISTRIBUTION

in seawater they simply float up to the surface and fly off. Their larvae are equally waterproof. Strongly attracted to rotting seaweed by its smell, the female kelp flies seek out warm spots in which to lay their eggs. The larvae hatch and feed on the seaweed around them. After three molts they pupate; the adults emerge and complete the life cycle about 11 days after the eggs were laid. Kelp flies are an important food source for several coastal birds, including kelp gulls and sandpipers.

LENGTH

SUBPHYLUM HEXAPODA

Bledius spectabilis

The most widely distributed of the seaweed flies, the kelp fly is found almost everywhere there is rotting seaweed along a strand line. They have flattened, lustrous black bodies, tinged with gray, and bristly, brownish yellow legs. Of the two pairs of wings, only the front pair is functional, the hind pair being modified to small clubshaped halteres that act as stabilizers when in flight. Kelp flies can crawl through vast layers of slimy seaweed without getting stuck, and if immersed

Osmia aurulenta

Important in the pollination of sand-dune plants, the dune snail bee has a compact, brownish black body with a dense covering of golden red hairs that later fade to gray. Unlike the honey bee, which carries any pollen it collects in pouches on its legs, the dune snail bee carries its pollen in a brush of hairs under its abdomen.

Intertidal Rove Beetle

Male bees of this species emerge between April and July, a little earlier in the year than the females, and seek out territories that contain a snail shell. They then leave scent marks (pheromones) on the stems of plants to attract passing females. Once a female has mated with her chosen partner, she will adjust the position of the shell so that the entrance is oriented in the most sheltered direction and lays her eggs inside it.

Dune Snail Bee 2/ 5

SUBPHYLUM HEXAPODA

Unusual in that it lives in the intertidal zone after which it is named, this small arthropod has an elongated, smooth black body. Short reddish brown wing cases, or elytra, protect the wings but leave most of the flexible abdomen exposed. A mobile abdomen allows the intertidal rove beetle to squeeze into narrow crevices and also to push its wings up under the elytra. Most rove beetles are active either by day (diurnal) or by night (nocturnal), but the life of the intertidal rove beetle is dictated by the tides. It builds a vertical, wine-bottle shaped burrow in the sand with a living chamber about 1/5 in (5 mm) diameter and retreats into it whenever the tide comes in. The burrow entrance is so narrow—about 1/10 in (2 mm) in diameter—that the air pressure within prevents any water from entering. The female lays her eggs in side chambers within the burrow and remains on guard, until her offspring have hatched and are mature enough to leave and construct their own burrows.

SUBPHYLUM HEXAPODA

DISTRIBUTION Coasts of northeastern Atlantic, North Sea, Baltic, and Mediterranean

SUBPHYLUM HEXAPODA

of them squeeze together in the fissures to avoid being immersed at high tide. It is here that they molt and lay their eggs safe from submersion and many of their predators. Rock springtails are blue-gray in color with segmented bodies that are wider at the posterior end. They have three pairs of appendages used for locomotion, which also allow them to swarm over the surface of calm rock pools without sinking—they cannot swim. Springtails are so named for their jumping organ, called the furcula, which acts like a spring, propelling the animal upward if threatened. Unlike other springtails, however, the rock springtail does not have this feature.

BRYOZOANS ATTACHED TO SEAWEED

Bryozoans

Bryozoans, such as this hard species encrusting a seaweed, often live in areas with strong currents.

THESE COLONIAL ANIMALS live

DOMAIN Eucarya KINGDOM Animalia

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attached to the sea bed and although SPECIES 6,085 numerous, they are often overlooked. The individuals making up the colony are usually less than 1/32 in (1 mm) long, but the colonies may span over 3 ft (1 m). Bryozoans are also called ectoprocts or sea mats, the latter name referring to their tendency to encrust the surfaces of stones and seaweeds. Other colonial forms of bryozoan include corallike growths, branched plantlike tufts, and fleshy lobes. Most species are marine, but a few live in fresh water. PHYLUM Bryozoa

Anatomy

Habitats

A bryozoan colony is made up of individuals called zooids, and may contain several or up to many millions. Each zooid is encased in a box-shaped body wall of calcium carbonate or a gelatinous or hornlike material, and a small hole links it to other zooids. To feed, the animal pushes a circular or horseshoe-shaped structure (a lophophore) out of an opening. This is crowned by tentacles covered in tiny, beating hairs that draw in planktonic food. In most species, fertilized eggs are stored in specialized zooids that form a brood chamber for developing larvae.

With their great variety of body form, bryozoans can be found in almost any habitat from the seashore to the deep ocean, and from Arctic waters to tropical coral reefs. Colonies are most often found firmly attached to BRYOZOANS UNDER ATTACK submerged rocks, seagrasses, seaweeds, Sea slugs often make a meal mangrove roots, and dead shells, but some of encrusting bryozoans, encrusting species even hitch a ride on the breaking into each zooid shells of living crustaceans and mollusks. A few and eating the insides. unusual species do not need a surface for support and can live in the sand; these bryozoan colonies can move slowly over or through the sand by coordinated rowing movements of a long projection found on specialized zooids. Bryozoan colonies originate from a single larva that settles on the seabed and becomes a zooid. More zooids are added to the colony by budding, a process in which a new zooid grows out from the side of the body wall. Most bryozoan larvae are short-lived and settle near the parent.

MAT OF ZOOIDS

This encrusting species of bryozoan has rectangular zooids joined in a single layer. The resulting mat spreads over seaweeds.

ORDER CTENOSTOMATIDA

ORDER CHEILOSTOMATIDA

Gelatinous Bryozoan

Hornwrack

Alcyonidium diaphanum

Flustra foliacea

DISTRIBUTION

SIZE (HEIGHT)

SIZE (HEIGHT)

Up to 12 in (30 cm)

Up to 8 in (20 cm)

DEPTH

DEPTH

0–656 ft (0–200 m)

0–330 ft (0–100 m)

HABITAT

HABITAT

Rocks and shelly sand

Stones, shells, rock

Temperate waters of northeastern

Atlantic

Temperate and Arctic waters of northeastern Atlantic

DISTRIBUTION

This species is often mistaken for a brown seaweed. The colony grows up from a narrow base as thin, flat, fan-like lobes. These usually form dense clumps and cover the sea bed like a crop of tiny brown lettuces. They litter the strandline on many shores in dried clumps and, by using a magnifying glass, an observer can easily see the individual, oblong colony members.

Pink Lace Bryozoan Iodictyum phoeniceum SIZE (WIDTH)

Up to 8 in (20 cm) DEPTH

50–130 ft (15–40 m) HABITAT

Rocky reefs DISTRIBUTION

Australia

Temperate and tropical waters around

Pink lace bryozoan colonies feel hard and brittle to the touch because the walls of the individual zooids are reinforced with calcareous material. The colony is shaped like curly-edged potato chips with a lacework of small holes.The beautiful dark pink to purple color remains even after the colony is dead and dried. This species prefers to live in areas with some current, and its holes may help reduce the force of the water against it. Similar species are found on coral reefs throughout the Indo-Pacific region.

OCEAN LIFE

Colonies of this bryozoan have a firm, rubbery consistency and grow as irregular, lobed, or fingerlike growths that attach to their substrate with a small, encrusting base. This species may cause an allergic dermatitis when handled, and North Sea fishermen are often affected when their trawl nets have gone through areas of dense bryozoan undergrowth.

ORDER CHEILOSTOMATIDA

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ANIMAL LIFE

Echinoderms THE NAME OF THIS PURELY MARINE

group of invertebrates is derived from the Greek for “hedgehog skin.” The group KINGDOM Animalia includes starfish, sea urchins, brittlestars, feather stars, and sea PHYLUM Echinodermata cucumbers. Echinoderms have radiating body parts, so most CLASSES 5 appear star-shaped, disc-shaped or spherical, and all have a SPECIES About 7,278 skeleton of calcium-carbonate plates under the skin. Inside is a unique system of water-filled canals, called the water-vascular system, that enables them to move, as well as to feed and breathe. Typically bottomdwellers, they live on reefs, shores, and the sea bed. DOMAIN Eucarya

RADIAL SYMMETRY

This tropical starfish has the typical fiverayed structure of echinoderms. Its arms are protected by hard plates, and its bright colors warn predators of its toxins.

Anatomy The echinoderm body is based on a five-rayed symmetry similar to the petals of a flower. This is apparent in starfish, brittlestars, and urchin shells (tests). Sea urchins are like starfish, with their arms joined to form a ball. Sea cucumbers resemble elongated urchins—their five-rayed symmetry can be seen end-on. The echinoderm skeleton is made of hard calcium-carbonate plates, which are fused to form a rigid shell (as in urchins) or remain separate (as in starfish). Usually, it also features spiny or knoblike extensions that project from the body. Sea cucumbers have minimal skeletons reduced to a series of small, isolated plates. The water-vascular system consists of a network of canals and reservoirs, as well as tentacles that extend through pores in the skin to form hundreds of tiny tube feet. outlet of water-vascular system (madreporite)

anus

tube foot spine

gonad

calciumcarbonate plate

watervascular canal

intestine

mouthparts

MINI SUCKERS

Tube feet act like hydraulic suckers. They are operated by water squeezed in and out from a small reservoir similar to the bulb on the end of an eye dropper.

SEA URCHIN BODY PLAN

The body consists of a fluid-filled cavity inside the shell (test), which houses the organs. The mouth is in the centre of the underside, and the anus is on top of the upper side.

OCEAN LIFE

ECHINODERM CLASSIFICATION The echinoderms are split into five classes based on their shape, skeleton, and the position of their mouth, anus, and madreporite. A sixth class, “the Concentricycloidea,” was at one time set up for the newly discovered sea daisies but these two species of disc-shaped animals are in fact a strange type of starfish and are now regarded as members of the class Asteroidea.

FEATHER STARS, SEA LILIES Class Crinoidea About 638 species

Also known as crinoids, these animals have a saucer-shaped body extending into five repeatedly branching, feathery arms used as filter-feeding appendages. Mouth and anus face upwards. Sea lilies attach to the sea bed by a jointed stalk, but feather stars break free when young to become swimming adults. STARFISH OR SEA STARS Class Asteroidea About 1,851 species

The body of these mostly seabed scavengers is star-shaped, with five or more stout arms

merging into a central body disc. On the underside of the arms are rows of numerous tube feet and a groove, along which they pass food to the central mouth. The mouth is on the underside, and the anus and madreporite are on the upper surface. The skeleton is a layer of plates (ossicles) embedded in the body wall.

SEA URCHINS, SAND DOLLARS Class Echinoidea

BRITTLESTARS, BASKET STARS Class Ophiuroidea

SEA CUCUMBERS Class Holothuroidea

About 2,074 species

About 1,716 species

These echinoderms have a disc-shaped body with five narrow, flexible arms. Basket stars’ arms are branched and finely divided. The skeleton is a series of overlapping plates. The mouth, on the underside, doubles as an anus.

These echinoderms have a sausage-shaped body with five double rows of tube feet, with those encircling the mouth modified into feeding tentacles. The skeleton comprises small, multi-shaped plates.

About 999 species

Body shape ranges from a disc (sand dollars) to a sphere (urchins) with five double rows of tube feet. The skeletal plates join to form a rigid shell (test) with movable spines.

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Reproduction Most echinoderms have separate males and females, which reproduce by releasing sperm and eggs, respectively, into the water. Individuals often gather to spawn at the same time, thereby increasing their chance of success. This synchronized spawning is initiated by factors such as daylight length and water temperature. Each echinoderm group has its own type of larva with its own way of swimming, floating, and feeding. Some starfish, for example, keep their fertilized eggs and developing larvae in a pouch under their mouth, and nourishment comes in the form of yolk. In some brittlestars, the larvae are brooded in sacs inside the body, and the young are released after metamorphosis. In most species, however, the fertilized eggs drift in the plankton and develop into free-floating larvae. The larvae eventually transform into their adult form and settle on the sea bed.

FLOATING AIDS

Long, paired arms help sea-urchin larvae, such as this one from a sea potato or heart urchin, to float in the plankton. Brittlestars have similar larvae.

RELEASING SPERM AND EGGS

By rearing up to spawn, sea cucumbers ensure that their eggs drift away to mix with sperm released by another individual.

Feeding Echinoderms range from peaceful grazers and filter feeders to voracious predators. Carnivorous species of starfish extend their stomach over their prey and digest it externally. In contrast, most sea urchins are grazers, scraping rock surfaces using teeth that resemble the chuck of an electric drill. Combined with muscles and skeletal plates, they form a complex, powerful feeding apparatus called Aristotle’s lantern. Sea cucumbers have an important role as sea-bed cleaners, vacuuming up organic debris and mud.

FILTER FEEDING BY TUBE FEET

Feather stars raise their arms to trap plankton using fingerlike tube feet. The food is trapped in mucus and passed down the arms into the mouth.

Defense

HUMAN IMPACT

PEDICELLARIAE

Slow-moving urchins and starfish can become overgrown by planktonic larvae looking for a place to settle. They defend themselves by using spines modified into tiny pincers, called pedicellariae, to catch and crush the larvae.

FIGHTING OVER OYSTERS In European waters, the common starfish has a voracious appetite for oysters and mussels. So, fishermen dredging the shellfish beds used to cut up the starfish and throw the pieces overboard. Unfortunately for the fishermen, this tactic proved ineffective, because starfish can not only regenerate their limbs, but if a lost limb retains part of the central body disk, it is able to completely regenerate the body. REGENERATING LIMBS

This common starfish is regrowing its two lost arms. Sometimes, regrowth produces one or more extra limbs.

OCEAN LIFE

If they can be broken open, sea urchins make a good meal for fish, sea birds, and sea otters. So, along with many other echinoderms, they protect themselves from predators with their long, sharp spines. These spines are mounted on ball-and-socket joints and can move in all directions, which turns them into fearsome weapons. If an echinoderm is attacked, spines may break off and embed themselves in the predator, creating a wound. Some spines are also venomous, such as those belonging to the crown-of-thorns starfish. Fire urchins and flower urchins also have enlarged and venomous, pincerlike pedicellariae (see below), which are strong enough to sting humans. The cumbersome-looking sea cucumbers have no spines or protective plates, but they are far from defenseless. If attacked, many eviscerate their gut (and sometimes other internal organs) as a decoy and regrow them later. Similarly, brittlestars can break free from attack by discarding an arm. Some tropical sea cucumbers eject sticky white threads, called Cuverian tubules, which are strong enough to entangle and restrain an attacking crab.

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ANIMAL LIFE CLASS ASTEROIDEA

Seven-arm Starfish Luidia ciliaris DIAMETER

Up to 24 in

(60 cm) DEPTH 0–1,300 ft (0–400 m)

Sediment, gravel, rock

HABITAT

DISTRIBUTION Temperate waters of northeastern Atlantic and Mediterranean

bury itself in the sediment and delve after its prey. Using its long tube feet it can move very quickly over rocks and gravel to latch onto its victims. This starfish is a voracious predator that feeds mainly on other echinoderms, including burrowing sea urchins, sea cucumbers, and brittlestars. It breeds during the summer in southern Britain but much earlier, between November and January, in the Mediterranean. multidirectional, stiff white spines on arm

While the majority of starfish species have five arms, this large species has seven arms and very occasionally eight. Its body and arms have a velvety texture and are colored brick-red to orange-brown. Each arm is fringed with a conspicuous band of multidirectional, stiff white spines, which help the seven- arm starfish to

CLASS ASTEROIDEA

Icon Star Iconaster longimanus DIAMETER

Up to 5 in (12 cm) DEPTH

100–280 ft (30–85 m) HABITAT

Deep reefs and slopes Tropical waters of Indian Ocean and western Pacific

DISTRIBUTION

This strikingly patterned species has long, thin arms and a flat disk. The arms and disk are edged by rows of skeletal plates that protect the starfish

velvety red or orange skin

CLASS ASTEROIDEA

Cushion Star Culcita novaeguineae DIAMETER

Up to 12 in (30 cm) DEPTH

0–100 ft (0–30 m) HABITAT

Coral reefs

LIVE-IN GUESTS The surface of the cushion star provides a home for a tiny shrimp, the sea-star shrimp Periclimenes soror. The shrimp does no harm to its host and is also found on other starfish. It often hides beneath the starfish and also matches its color to that of its host.

CLASS ASTEROIDEA

Goosefoot Starfish Anseropoda placenta DIAMETER

Up to 8 in (20 cm) DEPTH

and give it a rigid feel. These plates may be pale or dark and they form unique patterns on each individual, which enable researchers to recognize, track, and monitor individuals in the field. Data from such studies indicates that icon stars grow very slowly and suggests that the largest individuals may live as long as humans. Although icon stars usually live in deeper, dark waters, they are common at depths of 15–65 ft (5–20 m) around Singapore, probably because the water there is turbid and light levels are low. Females produce large orange eggs that develop into tiny orange larvae; the eggs contain chemicals that deter fish predators. portion of its disk is marked with a dark red patch, and conspicuous red lines radiate outward from this patch, along its arms. Its underside is colored yellow. This starfish glides slowly over the sea bed searching for small crustaceans, mollusks, and other echinoderms to eat.

30–1,600 ft (10–500 m)

DISTRIBUTION Adaman Sea and tropical waters of western Pacific

HABITAT

Gravel, sand, mud Temperate and warm waters of northeastern Atlantic and Mediterranean

OCEAN LIFE

DISTRIBUTION

The cushion star looks more like a spineless sea urchin than a starfish; it gets its name from its plump, rounded body. Its arms are so short that they merge with its body and only their tips can be seen. Juveniles are much flatter than adults and have a clear pentagonal star shape, with obvious arms. They hide under rocks to escape predators, whereas the tougher adults are relatively safe in the open. Cushion stars occur in a wide range of colors, from predominantly red to green and brown. The underside has five radiating grooves that represent the arms and are filled with tube feet. If the starfish is turned over, it can right itself by stretching out the tube feet on one side, anchoring them to the sea bed, and pulling. It feeds mainly on detritus and fixed invertebrates, including live coral. Two other similar species are found in the Indo-Pacific tropics but this one is the most common and widespread. thick, soft body

The goosefoot starfish gets its name from the appearance of the flattened, weblike disk that joins each of its five short arms together and produces an almost pentagonal shape. The central COMMENSAL SHRIMP

The sea-star shrimp seen here is on the underside of the cushion star but will venture out onto the top to feed.

CLASS ASTEROIDEA

Mosaic Sea Star Plectaster decanus DIAMETER

Up to 6 in (16 cm) DEPTH

30–600 ft (10–180 m) HABITAT

Rocky reefs DISTRIBUTION

Temperate waters of South Australia

The incredibly bright colors of this starfish are a warning that it contains toxic chemicals. It should not be picked up as it can cause numbness. A mosaic of raised yellow ridges covers its red upper surface and it has a soft texture. The mosaic sea star feeds mostly on sponges, and these may be the source of its toxins. When the females spawn, the fertilized eggs are retained and brooded on the underside of the body.

ECHINODERMS CLASS ASTEROIDEA

Crown-of-thorns Starfish Acanthaster planci DIAMETER

Up to 20 in (50 cm) DEPTH

3–65 ft (1–20 m) HABITAT

Coral reefs DISTRIBUTION

Tropical waters of Indian and Pacific

oceans

Occasional plagues of this large and destructive starfish sometimes kill extensive areas of coral on the Great Barrier Reef of Australia on reefs in the Indo-Pacific. There has been much debate on whether such plagues are natural or are caused by overfishing of their few predators, such as the giant triton, Charonia tritonis (see p.285). Land run-off appears to stimulate plagues. Recent research on the Great Barrier Reef suggests that some outbreaks are caused by

high input of nutrients from land. With up to 20 arms and a formidable covering of long spines, this species has few predators. The spines are mildly venomous and may inflict a painful wound if the starfish is picked up with bare hands. Crown-of-thorns starfish feed on corals by turning their stomach

309

out through their mouth and digesting the coral’s living tissue. Pure white coral skeletons indicate that this starfish has been feeding recently in the area. In popular diving tourism areas, attempts are often made to kill the starfish by injecting them with poison or removing them by hand, but with only limited success. A new experimental injection that promotes bacterial growth and induces an immune response may prove effective.

CLASS OPHIUROIDEA

Common Brittlestar Ophiothrix fragilis DIAMETER

Up to 5 in

(12 cm) DEPTH

0–500 ft (0–150 m)

Rocks, rough and gravely ground

HABITAT

DISTRIBUTION Temperate and warm waters of eastern Atlantic

CLASS OPHIUROIDEA

arm coiled around black coral branch

Serpent Star Astrobrachion adhaerens Up to 12 in

(30 cm) 50–600 ft (15–180 m)

DEPTH

Antipatharian black corals

HABITAT

DISTRIBUTION Tropical and temperate waters of Australia and southwestern Pacific

orange to brown and gray, and they often have alternate light and dark bands on the arms. The fragile arms of this species are covered in long, untidy spines, while its small disk, which is only 1 in (2 cm) across, has a covering of shorter spines. In the intertidal zone, common brittlestars are not usually found in groups, but occur as individuals hiding in crevices and beneath stones.

OCEAN LIFE

DIAMETER

Serpent stars are a type of brittlestar with long, flexible arms. During the day they wind their arms tightly round the branches of the deep-water black corals in which they live. At night they uncoil their arms and move around, feeding on the living polyps of their host. A black coral bush one or two yards high may be host for up to forty or so serpent stars.

This large brittlestar species gathers in dense groups that may cover several square miles of sea bed in areas where there are strong tidal currents. They have been recorded at densities of 2,000 individuals per square yard. Each brittlestar holds up one or two arms into the current to feed on plankton, while linking its remaining arms with surrounding individuals to form a strong mat and prevent itself being swept away. They vary greatly in color, ranging from red, yellow, and

310

ANIMAL LIFE CLASS ECHINOIDEA

Sand Dollar Echinodiscus auritus DIAMETER

Up to 11cm (4in) DEPTH

0–50m (0–165ft) HABITAT

Clean sand Tropical and warm waters of Indian Ocean, Red Sea, western Pacific DISTRIBUTION

CLASS ECHINOIDEA

Long-spined Sea Urchin Diadema savignyi DIAMETER

Up to 23cm

(9in) DEPTH

0–70m (0–230ft)

HABITAT

Coral and rocky

reefs DISTRIBUTION

Pacific oceans

Tropical waters of Indian and western

Sand Dollars are sea urchins that have become extremely flattened as an adaptation for burrowing through sand. A mat of very fine spines covers the shell, or test, and the pattern of the animal’s skeleton plates can often be seen through the skin. The mouth is on the underside. At the rear are two notches that open at the margins of the test, and water currents passing through these slits are thought to help to push the urchin down and prevent it being swept away. Many divers on coral reefs have learnt to avoid these sea urchins. They bristle with long, sharp spines that can easily wound, even through a wetsuit. The spines are mildly venomous and so brittle that they may break off in the wound. If a diver or predator comes near to it, this sea urchin waves its spines about vigorously. Only a few tough fish, such as the Titan Triggerfish, can successfully attack and eat such prickly prey. This species often has striped spines, while the other common Indo-Pacific long-spined species, Diadema setosum, has black spines.

CLASS ECHINOIDEA

Flower Urchin Toxopneustes pileolus DIAMETER

Up to 15cm (6in) DEPTH

0–90m (0–300ft) HABITAT

Sand, rubble, rocky reef Tropical waters of Indian Ocean, central and western Pacific Ocean

DISTRIBUTION

This species is extremely venomous and has caused rare fatalities. It has short, inconspicuous spines through which emerge an array of flower-like appendages called pedicellariae. These help to keep the urchin’s surface clean

but will sting animals that touch it. The pedicellariae also hold pieces of shell, rubble, and seaweed that shade the urchin from sunlight. Flower Urchins may partially bury themselves, despite having few predators.

CLASS ECHINOIDEA

Edible Sea Urchin Echinus esculentus DIAMETER

Up to 16cm (6in) DEPTH

0–50m (0–160ft) HABITAT

Rocky areas DISTRIBUTION

Temperate waters of northeastern

Atlantic

This large, spherical urchin is covered with uniform short spines that give it the appearance of a fat hedgehog. It is generally a pinkish colour, with pairs of darker, radiating lines where its numerous tube feet emerge. These urchins are important grazers and can have much the same effect underwater as rabbits do on land, leaving the rocks covered only in hard pink encrusting algae. As their name suggests, the roe of this species can be eaten.

CLASS ECHINOIDEA

Purple Sea Urchin Strongylocentrotus purpuratus DIAMETER

Up to 10cm (4in) DEPTH

0–40m (0–130ft) HABITAT

Rocky reefs Temperate coastline of North America from Alaska to Mexico

OCEAN LIFE

DISTRIBUTION

This small sea urchin has been responsible for the demise of large areas of giant kelp forest off the North American coastline. Like most sea urchins, it feeds by scraping away at seaweeds and fixed animals and its favourite food is the giant kelp Macrocystis pyrifera. Its numbers reach densities of up to several hundred animals per square metre, and it can chew through kelp holdfasts, setting the plants adrift. Populations are normally kept in check by Sea Otters and by large fish such as sheepheads. In the past, when Sea Otters were hunted, urchin numbers increased explosively in some areas.

311 CLASS ECHINOIDEA

Sea Potato Echninocardium cordatum Up to 9cm (31/2 in)

LENGTH

0–200m (0–650ft)

DEPTH

HABITAT

Sand, muddy

sand DISTRIBUTION

Temperate waters of northeastern

Atlantic

Most sea urchins live in rocky areas, but the Sea Potato or Heart Urchin burrows in the sand. Unlike regular urchins it has a distinct front end and its spines are thin and flattened. Special spoon-shaped spines on the urchin’s underside help it to dig, while longer spines on its back allow water to funnel down into its burrow to be used for respiration. The dried shell, or test, of this urchin resembles a potato, hence the common name.

CLASS CRINOIDEA

Sea Lily Neocrinus decorus HEIGHT

Up to 60cm

(24in) DEPTH 150–1,200m (500–4,000ft) HABITAT Deep-sea sediments DISTRIBUTION

Tropical waters of western Atlantic

Ocean

Sea lilies are stalked relatives of feather stars and usually remain fixed in the same place after developing from a settled planktonic larva. However,

CLASS CRINOIDEA

Tropical Feather Star Oxycomanthus bennetti DIAMETER

Up to 15cm (6in) DEPTH

10–50m (33–165ft) HABITAT

Coral reefs DISTRIBUTION

Tropical waters of western Pacific

All that can usually be seen of the Tropical Feather Star is its numerous feathery arms held up into the water to trap food. This species has about a hundred arms, compared to the ten that most temperate water feather stars have. The arms are attached to a small, disc-like body and the mouth is on the upper side of the

while Neocrinus decorus and other, similar sea lilies cannot swim as shallow-water feather stars do, they have been filmed dragging themselves over the sea bed by their arms. To do this, they appear to break off the end of the stalk, then re-attach to the substrate using flexible, finger-like appendages on the stalk. In this way they can escape from predatory sea urchins. The stalk consists of a stack of disc-shaped skeleton pieces called ossicles, and looks like a simple vertebrate spinal column. Sea lilies feed by spreading out their numerous, feathery arms against the current and trapping plankton. Food particles are passed down the arms and into the mouth.

DISCOVERY

FOSSIL EVIDENCE Today there are relatively few sea lily species, all of which live in deep water, but this group once thrived in ancient seas. Entire fossil sea lilies such as this one are rare, but loose ossicles from their stalks are very common in some limestones.

body, between the arms. The Tropical Feather Star clings onto corals using numerous articulated, finger-like appendages called cirri. It prefers elevated positions where it is exposed to food-bearing currents, and is active by both day and night. Like all feather stars, this species starts its early life by becoming attached to the sea bed by a stalk – at this stage, it closely resembles a small sea lily. As it matures, the feather star breaks away and becomes free-living, leaving the stalk behind.

CLASS CRINOIDEA

Passion Flower Feather Star Ptilometra australis DIAMETER

Up to 12cm

(5in) DEPTH

To at least 60m

(200ft) Rocky reefs,

rubble DISTRIBUTION Endemic to temperate waters of southern Australia

This stout feather star has 18–20 arms with long, stiff side branches called pinnules; the arms are different lengths, giving it a flower-like appearance when viewed from above. They are

OCEAN LIFE

HABITAT

called passion flowers by fishermen because they are brought up in large numbers by commercial trawlers, clinging tightly to their nets. These feather stars are found in reefs and also in very shallow, sheltered bays and estuaries. Like most feather stars, the Passion Feather Star is a filter feeder that grips onto the tops of rocks, sponges, and sea fans, where it spreads its arms wide to trap plankton and suspended detritus. It remains expanded both day and night but, like other feather stars, it can curl up its arms if disturbed or while resting. Its usual colour is a burgundy red.

312

CLASS HOLOTHUROIDEA

Prickly Redfish Thelenota ananas LENGTH

Up to 28 in

(70 cm) DEPTH

16–100 ft (5–30 m)

Sandy areas of coral reefs

HABITAT

DISTRIBUTION Tropical waters of Indian Ocean and western Pacific

This massive sea cucumber looks like an animated rug as it crawls slowly over the sea bed. The large, star-shaped papillae, called caruncles, that cover its

CLASS HOLOTHUROIDEA

Sea Cucumber Bohadschia graffei LENGTH

Up to 12 in (30 cm)

body make it an unattractive proposition to potential predators. However, its appearance does not deter humans, and prickly redfish fetches high prices in parts of eastern Asia, where it is considered a delicacy. As a result, it is now endangered. Large specimens reach up to 11 lb (5 kg) in weight and are traditionally collected

CLASS HOLOTHUROIDEA

Edible Sea Cucumber

Sea Apple Pseudocolochirus violaceus LENGTH

Up to 4 in (10 cm) LENGTH

DEPTH

0–100 ft (0–30 m)

DEPTH

HABITAT

HABITAT

15–100 ft (5–30 m) HABITAT

Tropical waters of Indian Ocean, Red Sea, western Pacific DISTRIBUTION

Sand, rock, coral reefs DISTRIBUTION

Tropical waters of Indian and Pacific

oceans

As its name suggests, this is an edible species of sea cucumber, although it is not considered as good eating as others, such as the prickly redfish (above). It has a soft body, peppered with tiny warts, and is colored black on its back and pinkish red to beige underneath. Like many other large sea cucumbers, it is sometimes host to small pearlfish (family Carapidae) that live inside its body cavity.

OCEAN LIFE

DEPTH

Up to 14 in (35 cm)

Coral reefs

sea bed in search of detritus to eat. When spawning, prickly redfish gather together and rear up, then release eggs or sperm into the water from small pores near the head end of the body.

CLASS HOLOTHUROIDEA

Holothuria edulis

15–165 ft (5–50 m)

The juveniles of this sea cucumber look completely different from the adult (shown here). They are white with black lines and protruding yellow papillae, closely resembling sea slugs from the genus Phyllidia. These slugs are distasteful to fish, so this mimicry protects the young sea cucumbers. Bohadschia graeffei feeds by scooping sand and mud into its mouth using large black tentacles, which are modified tube feet. Organic material in the sediment is digested, while the remainder passes through the gut and is deposited outside, looking like a string of sausages. In areas where sea cucumbers are common, much of the surface sediment is vacuumed up and cleaned several times a year in this way.

by reef walking at low tide or by breath-hold diving. Other predators include various fish and crustaceans. The flat underside of the prickly redfish is covered with orange tube feet, which it uses to crawl over the

Rocks and reefs DISTRIBUTION

Tropical waters of Indo-Pacific region

The sea apple is one of the most colorful of all sea cucumbers and is widely collected for use in marine aquariums. It has a red and purple body and yellow tentacles. The species in the genus Pseudocolochirus are often hard to distinguish and for this reason the distribution map may include

CLASS HOLOTHUROIDEA

Deep-sea Cucumber Laetmogone violacea LENGTH

Not recorded

To at least 8,000 ft (2,500 m)

DEPTH

Soft sediments

HABITAT

Deep, cold waters of Atlantic, Indian, and Pacific oceans

DISTRIBUTION

In the deep ocean, sea cucumbers are one of the dominant sea-floor groups all over the world. Laetmogone violacea is one of a large number of species that crawl over the soft, muddy ocean bottom eating organic detritus. Its peglike “legs” may help to keep it from sinking too far into the mud. Ingested mud that the cucumber is

several species. The sea apple uses its tube feet to attach itself to rocks then extends its branched tentacles into the water to trap organic particles. From time to time, each tentacle is pushed into the mouth and the food it has trapped is wiped off. unable to digest leaves its body as fecal casts, which may then be eaten again by other sea cucumbers. Like many deep-sea animals, this sea cucumber is almost colorless but glows all over with bioluminescent light; exactly how the animal uses this light is not yet known. Some deep-sea starfish are known to light up when approached by a predator, which may scare it away. It may be that the deep-sea cucumber uses its bioluminescence in the same way.

SMALL, BOTTOM-LIVING PHYLA

313

Small, Bottom-living Phyla MANY DISPARATE INVERTEBRATES

play important parts in marine ecosystems but are seldom seen, because they are small or their habitats are difficult to study. Like KINGDOM Animalia all animals, they are grouped into phyla, each phylum representing an apparently PHYLA 10 distinct body plan. Most of these small, bottom-living phyla live in seabed sediment SPECIES Many and are loosely called “worms” due to their shape and burrowing lifestyle. However, the superabundant nematodes or roundworms of which there are 28,000 described species and possibly a million in total, live in a wide range of environments, including the seabed. A selection of 10 bottom-living phyla are represented below. DOMAIN Eucarya

Sand-grain Animals

SAND COMMUNITY

A community of tiny animals, referred to collectively as meiofauna, lives in the surface water film between the sand grains on beaches and in shallow water. They range in size from 1/100 in to 1/2 in (0.05 mm to 1 mm) and so can only be seen well with a microscope. Many have intricate and beautiful shapes. Almost every marine invertebrate phylum has representative species that live in this habitat, and several phyla, such as tardigrades (water bears) and gastrotrichs, occur virtually nowhere else. A diverse meiofauna is a good indication of a healthy environment, since these minuscule organisms are the basis for many marine food chains.

Many invertebrates exist in the watery spaces between grains of coastal sand. The wormlike gastrotrich (phylum Gastrotricha) shown in this photo-micrograph is one of many species found in this habitat.

Mud-swallowers FEEDING APPARATUS

Female spoonworms (phylum Echiura) sweep up organic material and sediment with a scooplike proboscis, seen here extending from a burrow.

The consistency and structure of seashore and seabed sediments depends largely on the many wormlike phyla that live there. Millions of these burrowing animals continually mix and rework the sediment, a process called bioturbation. Lugworms (see p.274) are famous for their ability to eat sand, depositing the inedible material on the sand surface in the form of coiled heaps, or casts, but many of the less well-known groups, including peanut worms, acorn worms, and kinorhynchs, are just as important. Organic material washed onshore with each tide or carried by currents is quickly incorporated into the sediment as the animals move around, or is processed as the surface mud is eaten.

New Phyla Scientists have so far described only a fraction of the species that live in oceans. New species are being discovered all the time, mostly in groups such as sponges and soft corals that traditionally have been neglected. Occasionally a species is found that is fundamentally different from all other known organisms and so it is classified as belonging to a new phylum. Most of these exciting discoveries are from inaccessible areas such as deep-sea mud, and the animals are usually small. But when the abundant life around deep-sea hydrothermal vents (see p.188–89) was sampled in the 1970s, gigantic tube worms like no others were found.

NEW SPECIES

These sedentary worms (phylum Phoronida) live in small tubes buried in sand or mud or (as here) attached to seabed rocks. To feed, the worms extend a horseshoe shaped net of tentacles.

OCEAN LIFE

HORSESHOE WORMS

Symbion americanus (above) lives on the mouthparts of the American lobster (left). It was first described in 2006, and is the second species in a new phylum of animals, the Cycliophora (see p.316).

314 PHYLUM HEMICHORDATA

Acorn Worm

Peanut Worm

Glossobalanus sarniensis

Golfingia vulgaris

SIZE

Not recorded Shallow water

DEPTH

HABITAT

PHYLUM PHORONIDA

Horseshoe Worm Phoronis hippocrepia Up to 4 in (10 cm)

LENGTH

0–165 ft (0–50 m)

DEPTH

HABITAT

Rocks and empty shells

Shallow coastal waters of Atlantic Ocean, northeastern and western Pacific DISTRIBUTION

Horseshoe worms are easily overlooked but they sometimes cover large areas of rock with their narrow, membranous tubes. The animal lives inside its tube,

PHYLUM NEMATODA

Roundworm Dolicholaimus marioni Up to 1/2 in (5 mm )

LENGTH

Intertidal

DEPTH

HABITAT

Among algae in rock pools

DISTRIBUTION

Shores of the northeastern

Atlantic

The peanut worm is shaped like a half-inflated sausage balloon. Its body is stout and has a long, thin region at the front called the introvert, which can be stretched right out or withdrawn completely inside the body. The animal has a crown of short tentacles around the mouth at the end of the introvert. It lives buried in sediment, which it eats as it burrows and digests any organic matter.

Up to 6 in (15 cm)

DEPTH

3 –330 ft (1–100 m)

HABITAT

Coastal temperate waters of northeastern Atlantic and Mediterranean

OCEAN LIFE

Female spoonworms have a proboscis that stretches out like an elastic band and can reach at least 3 ft (1 m) away in search of food. The worm’s green, pear-shaped trunk remains hidden between rocks, safe from predators. In this species, the tip of the proboscis

is forked, and usually this is all that can be seen of the worm. The proboscis collects food particles with the help of sticky mucus, and the food is moved along the proboscis and into the mouth by the whipping movements of hairlike cilia. Male spoonworms are tiny and parasitic on the females, their only function being to fertilize the female’s eggs.

plump body

extended introvert

Pterobranch Worm Rhabdopleura compacta Up to 1/2 in (5 mm)

LENGTH DEPTH

Not recorded

HABITAT

Attached to sessile animals

DISTRIBUTION

Cold waters of northern hemisphere

Like the acorn worms to which they are related (above, left), pterobranch worms live in a thin tube and their bodies are divided into a proboscis, collar, and trunk. They also have a pair of arms covered in tentacles arising from the collar region. The tubes of many individuals are connected together with strands of soft tissue that join the trunks of the animals, enabling them to form a colony.

PHYLUM CEPHALORHYNCHA

Priapula Worm Priapulus caudatus Up to 4 in (10 cm) Not recorded Buried in sediment

Arctic Ocean

Muddy rocks

DISTRIBUTION

Northeastern Atlantic and eastern Mediterranean; possibly Indo-Pacific, Southern Ocean

PHYLUM HEMICHORDATA

DISTRIBUTION

Bonellia viridis

Muddy sand and gravel

The soft, slimy body of this wormlike animal is divided into three regions. At the front end is a pointed proboscis, separated from the long, thin trunk by a tubelike collar. It lives in a U-shaped burrow and feeds by trapping small organisms in sticky mucus and eating sediment. The sexes are separate, and reproduction can be either asexual, by fragmentation or budding, or sexual. Some biologists group acorn worms with pterobranch worms (see below) in one phylum, the Hemichordata. Unusually for invertebrates, they have some vertebrate characteristics, which include a nerve cord that runs along the back.

HABITAT

Spoonworm

HABITAT

DISTRIBUTION

DEPTH

PHYLUM ECHIURA

0–6,560 ft (0–2,000 m)

DEPTH

Coastal temperate waters of northeastern Atlantic

LENGTH

LENGTH

Soft sediments

Up to 8 in (20 cm)

LENGTH

DISTRIBUTION

which encrusts rock surfaces or can bore into shells or limestone rock so that only the top part of the tube shows. The end of the wormlike body is thickened and anchors the animal in its tube. The feeding head with its horseshoe of delicate ciliated tentacles is extended to catch tiny planktonic animals while the body remains hidden in the tube. The feeding head is called a lophophore and is found in all members of the phylum. Horseshoe worms brood their egg masses within the lophophore, and larvae are continually released to drift and develop in the water. It is hard to see which end is which on a roundworm, as both ends of its thin body are pointed. The body is round in cross-section and has longitudinal muscles but no circular ones. This results in a characteristic way of moving in which the body is thrashed in a single plane forming C- or S-shapes in the process. This is a marine species, but roundworms also occur in vast numbers in the soil and fresh water.

PHYLUM SIPUNCULA

Cold waters of north Atlantic and

The stout, cylindrical body of this animal is divided into a short barrelshaped proboscis at the head end, a longer trunk region, and a tail that consists of small bladders attached to a hollow stalk. The proboscis can be withdrawn into the trunk. The mouth on the end of the proboscis is edged with spines, which help the animal to seize other small marine worms for food.

SMALL, BOTTOM-LIVING PHYLA PHYLUM VESTIMENTIFERA

PHYLUM CEPHALORHYNCHA

Mud Dragon

Linguid Brachiopod

Echinoderes aquilonius

Glottidia albida

Less than 1mm

LENGTH

Shallow water

DEPTH

HABITAT

Muddy sediments

DISTRIBUTION

Northwestern Atlantic

Mud dragons resemble miniature insect pupae. The body appears segmented on the outside but this is superficial. It is covered with a thick, articulated cuticle and sharp spines on each body section. The tail end has a bunch of longer spines, and the head region has several rings of spines. The mouth is situated on the end of a cone-shaped structure. The animal can withdraw the entire head region into the rest of the body for protection, but it can also close the resulting hole with special plates, which are called placids. The head spines help the animal to push its way through the sediment, feeding on organic debris, bacteria, protists, and diatoms. The 100–150 species of mud dragons are all marine. The sexes are separate but look similar. The eggs develop into free-living larvae that moult several times before attaining the adult form.

PHYLUM BRACHIOPODA

Lamp Shell Terebratulina septentrionalis Up to 11/4 in (3 cm)

LENGTH DEPTH

0–4,000 ft (0–1,200 m)

HABITAT

Rocks and stones

DISTRIBUTION

Atlantic

Temperate and cold waters of north

pulling itself down with its pedicle. Fossils of brachiopods with a similar shape appear in rocks that are 500 million years old.

1 in (2 cm)

HEIGHT DEPTH

315

0–1,476 ft (0–450 m )

HABITAT

Subtidal sediment

Coastal waters of northeastern Pacific, California to Mexico DISTRIBUTION

Linguid brachiopods resemble small clams with strange long tails. The tail is, in fact, a stalk, known as a pedicle, that emerges from between the brachiopod’s shell valves. Brachiopods have a two-part shell similar to a clam, but these two types of animals are not closely related. Many brachiopods use their pedicle to attach to rocks (see lamp shell below), but lingulid brachiopods live in burrows in sand and mud. The pedicle is two to three times the length of the shell and is used to make a burrow in the soft sediment in which it lives. When filtering plankton from the water it comes to the top of the burrow and opens its shell using special muscles, but the linguid brachiopod can quickly disappear by It would be easy to mistake a lamp shell for a small bivalve mollusk, as both have a hinged shell in two parts and live attached to the sea floor. lamp shells, however, have a very thin, light shell and the two parts are different sizes, with the smaller one fitting into the larger. The shell valves cover the dorsal and ventral surfaces of the animal whereas in bivalve mollusks they are on the left and right side of

the body. Most lamp shells attach their pear-shaped shell to hard surfaces by means of a fleshy stalk that emerges from a hole in the ventral shell valve. With the shell valves gaping open, the animal draws in a current of water that brings plankton with it. Taking up most of the space inside the shell is a feeding structure called the lophophore, which consists of two lateral lobes and a central coiled lobe

covered in long ciliated tentacles. The beating of the cilia creates the water current. Lamp shells are found worldwide, but they are especially abundant in colder waters. In the northeastern Atlantic, Terebratulina septentrionalis is mostly found in deep water, while along the east coast of North America, it commonly occurs in shallow water. This species is very similar to Terebratulina retusa.

OCEAN LIFE

316

ANIMAL LIFE PHYLUM TARDIGRADA claw

Pseudobiotus Water Bear Pseudobiotus magalonyx LENGTH

Up to 1mm

DEPTH

Shallow water

HABITAT

Muddy sediments

DISTRIBUTION

Northwestern Atlantic

Although still tiny, this water bear is one of the largest and can be found by sampling tidal mud flats in the upper estuaries of rivers in northern Europe. The female in the photograph below has laid her eggs in her own molted cuticle, which she holds like a knapsack on her back. This is one of the few tardigrades that have been seen to mate. Males of this species grip the female and deposit sperm through the cloacal opening of her molted cuticle.

gut

stubby leg

PHYLUM TARDIGRADA

Echiniscoides Water Bear Echiniscoides sigismundi Less than 1 mm

LENGTH DEPTH

Not recorded

HABITAT

Marine sands

DISTRIBUTION

Worldwide

This species of water bear lives in the spaces between sand grains in marine sediments, as do most of the other 25 or so marine species. The rest of the 400 or so other species live in fresh water, especially in the thin layer of water around damp-loving plants such as mosses. Water bears have a short, plump body without a well-defined head but with eyespots and sensory appendages at one end. There are four pairs of short stubby legs each

ending in a bunch of tiny claws on which the animal lumbers slowly along. The relatively thick skin protects against abrasion from sand grains. The sexes are separate, but there are few males and the eggs can probably develop without being fertilized. The nearest relatives of these tiny animals are thought to be arthropods. Water bears are so tough that terrestrial species can withstand drying and freezing.

PHYLUM CYCLIOPHORA

Cycliophoran

Gastrotrich

Symbion pandora

Turbanella species

0.3 mm

LENGTH DEPTH

Not recorded

HABITAT

Mouthparts of the Norway Lobster

DISTRIBUTION

OCEAN LIFE

PHYLUM GASTROTRICHA

North Sea

This species was first described in 1995 by two Danish biologists. It was found clinging to the mouthparts of a Norway lobster (Nephrops norvegicus) that was dredged up from the North Sea, and the biologists must have looked very closely to have seen it at all. Individuals have a rounded body and are attached to the substratum by a short stalk and adhesive disk. They feed by means of a mouth funnel surrounded by cilia and excrete via an anus next to the mouth. This feeding stage is neither male nor female, and the reproductive cycle is complex involving both sexually and asexually produced free-swimming larvae. Symbion pandora was the first representative of the phylum cycliophora. It has since been joined by a second species, S. americanus, discovered in 2006, which lives similarly on the American lobster (Homarus americanus). Molecular studies show that both species may be related to bryozoans (p.305) and tiny animals called entoprocts. It seems likely that, with a careful search, other species will soon be discovered.

Less than 1 mm

LENGTH DEPTH

Not recorded

HABITAT

Well-oxygenated sediments

DISTRIBUTION

Not recorded

Gastrotrichs are found in both fresh water and the sea, but Turbanella is a marine genus that lives in the spaces between sand grains in sea-floor sediments. It looks similar to a ciliated protist, but is a true multicellular animal with a mouth, gut, kidney cells, and other structures. It has several adhesive tubes, structures that secrete a sticky substance and help the animal attach to the substratum. By attaching and detaching the adhesive tubes at the front and rear of its body, it can loop around rather like a leech. Alternatively, it can glide using its cilia, searching for bacteria and protists to eat.

gut

cilia

PLANKTONIC PHYLA

317

Planktonic Phyla OF THE MANY MAJOR GROUPS

(phyla) of invertebrate animals, a few are entirely composed of planktonic animals. Like all animals, they are classified into different phyla based on their anatomy, which can be complex. All are ecologically important because the plankton community underpins all the ocean food chains. Three minor phyla (Ctenophora, Chaetognatha and Rotifera) are represented here.

DOMAIN Eucarya KINGDOM Animalia PHYLA Ctenophora Chaetognatha Rotifera SPECIES About 2,332

Predators Carnivorous zooplankton have many methods of catching prey. Comb jellies are voracious predators—some trap their prey with a sticky secretion released from special cells (colloblasts) lining their tentacles. Others draw in prey using negative pressure created by rapidly opening their mouths. Species of Haeckelia even recycle the stinging cells from their cnidarian prey. Arrow-worms have vibration sensors to detect prey, which is caught and held by moveable hooks. The prey is then paralyzed by neurotoxins released from pores adjacent to the mouth.

HOOKING PREY

This arrow-worm has brown-colored hooks on either side of its circular mouth for holding prey.

Grazers

ROTIFER FEEDING METHOD

The rotifer’s ciliated crown, used in locomotion and filter feeding, is visible on the left.

Some of the zooplankton are herbivorous, grazing on phytoplankton or filter feeding. Some planktonic rotifers feed on organic particles suspended in the water. The cilia on the crown that surrounds the oral cavity waft water into a food groove leading to the mouth. Here, food particles are sifted and returned to the pharynx where jawlike structures, called trophi, grind the food before it passes into the stomach. Trophi are unique to rotifers. creeping comb jelly

PHYLUM CTENOPHORA

Creeping Comb Jelly Coeloplana astericola DIAMETER 1/2

in (1 cm)

DEPTH

Not recorded HABITAT

On the orange sea star DISTRIBUTION

Tropical waters of western Pacific

While most comb jellies live in the plankton, creeping comb jellies have taken up a bottom-living existence. Instead of the more usual rounded shape, they are flattened and look like

GLEAMING CILIA

Comb jellies, or sea gooseberries, swim by beating eight vertical rows of cilia combs, which shimmer with iridescent colors.

PHYLUM CTENOPHORA

a tiny squashed ball. The mouth is in the center of the underside with the statocyst, a balancing organ found in all comb jellies, opposite it on the upper side. Comb rows are absent as they have no need to swim, and they move by muscular undulations of the body rather like a small flatworm. This species lives on the orange sea star (Echinaster luzonicus), lying still and PHYLUM CTENOPHORA

Predatory Comb Jelly Mnemiopsis leidyi LENGTH

Up to 3 in (7 cm) DEPTH

0–100 ft (0–30 m)

Temperate and subtropical waters of western Atlantic, Mediterranean, and Black Sea

DISTRIBUTION

This comb jelly is a slightly flattened pear shape and has two rounded lobes on each side of the mouth that help it to surround and enclose larger prey. As well as two main feeding tentacles,

Cestum veneris LENGTH

Up to 61/2 ft (2 m) DEPTH

Near surface HABITAT

Open water DISTRIBUTION Tropical and subtropical waters of north Atlantic, Mediterranean, and western Pacific

almost invisible during the day, its color and mottled pattern matching its echinoderm host. At night, it extends its two long feeding tentacles to ensnare planktonic prey. there are smaller secondary tentacles in grooves surrounding the mouth. The long tentacles are armed with lasso cells that secrete a sticky material to ensnare prey. The predatory comb jelly, which is native to the western Atlantic, was accidentally introduced to the Black Sea in the 1980s by the release of ship ballast water, and it has since spread to adjacent bodies of water, including parts of the eastern Mediterranean. In the Black Sea, it multiplied rapidly because of the ideal water conditions and the absence of its natural predators. This has had very serious effects on commercial fish catches because the predatory comb jelly is a planktonic predator and consumes fish larvae and fry.

The unusual name of this animal comes from the ribbon shape of its transparent, pale violet body. Eight rows of comb cilia are modified and run in two lines along one edge of the ribbon. The two main tentacles are short, and numerous other short tentacles occur along the lower edge of the body. As an escape response, Venus’s girdle can swim rapidly by undulating its body. However, more usually it moves slowly by beating its comb cilia.

OCEAN LIFE

HABITAT

Open water

Venus’s Girdle

318

ANIMAL LIFE

Tunicates and Lancelets

Anatomy

TUNICATES HAVE A LONG,

baglike body often attached to the sea floor; lancelets resemble small, stiff worms and live buried in sediment. Despite their simple appearance, these animals are included not with the world’s other invertebrates but in the same group as backboned animals such as fish and mammals. This is because, uniquely among invertebrates, tunicates and lancelets possess an internal skeletal rod, or notochord. The best-known tunicates are sea squirts, some of which form colonies, whereas lancelets are all solitary.

DOMAIN Eucarya KINGDOM Animalia PHYLUM Chordata SUBPHYLA Tunicata Cephalochordata CLASSES 5 SPECIES About 3,056

Lifestyle

When tunicate larvae become adults, they lose the supporting notochord, but lancelets keep it during the adult stage. Tunicates are covered by a tough protective bag made out of cellulose called a tunic, which sticks to the sea floor by means of rootlike projections. Inside is a big sievelike structure, the pharynx, which connects the mouth and gut. This has a sticky mucus coating to trap plankton from the seawater passing through it. Lancelets also filter water through a pharynx, expelling it through an opening near the anus. A ring of stiff hairs (cirri) surrounding their mouth prevents sand getting in. pharynx

LANCELET ADULT

Sea squirts live attached to hard surfaces such as rocks, reefs, and shipwrecks. They spend their time filtering seawater, drawing in food-rich water through one siphon (inhalent) and releasing waste water through another (exhalent). Most sea squirts occur in shallow coastal waters where there is plenty of plankton, but there are also a few deep-water species. In sheltered sea lochs, they can cover hundreds of square yards of sea bed. Some tunicates, including salps and pyrosomes, drift along on ocean currents with the plankton, often forming giant swarms. Lancelets are strong swimmers due to their flexible, muscular bodies, but they usually just burrow in sediment with only their head sticking out.

BOTTOM-LIVING SQUIRTS

Sea squirts sometimes grow together in clumps with cnidarians, and sea sponges, and they can be very colorful.

dorsal nerve cord notochord

A lancelet’s muscular body is flattened from side to side and is supported by a stiff notochord. swimming muscles

cirri surrounding mouth

anus

TUNICATE LARVA

The tadpole-shaped tunicate larva‘s nerve cord and notochord are reabsorbed when it changes into the adult form. nerve cord siphon

notochord

pharynx attachment organ heart

inhalent siphon exhalent siphon tunic pharynx water current digestive gland ovary heart gut

SWIMMING SQUIRT

TUNICATE ADULT

Floating salps swim by jet propulsion, taking in water at one end and squirting it out of the other.

Most of the space inside a tunicate is taken up by the huge pharynx, visible through the tunic of this translucent species.

SUBPHYLUM TUNICATA

Common Sea Squirt Ciona intestinalis HEIGHT

Up to 6 in

(15 cm) DEPTH 0–1,600 ft (0–500 m)

Any hard substrate

HABITAT

OCEAN LIFE

DISTRIBUTION Atlantic, Pacific, Indian, Arctic oceans; possibly Southern Ocean

The common sea squirt has no supporting structures in its adult form, so when it is seen out of water, it resembles a blob of jelly that may squirt out a jet of water when prodded. It is a typical solitary tunicate, whose internal structures are visible through its pale, greenish yellow, gelatinous outer covering, called a test or tunic, which is smooth and translucent. It has two yellow-edged

siphons and uses the larger of these, the inhalent siphon, to draw in water; the smaller, exhalent siphon is used to expel water, and its opening has six lobes, while that of the exhalent siphon has eight. The common

sea squirt lives up to its name and is found attached to a wide variety of rocks, reefs, seaweeds, and, in particular, man-made structures. The legs of oil platforms and jetties, for example, are often festooned with this sea squirt.

CLEANING UP In sheltered sea lochs and harbors, the common sea squirt often covers large areas of rock or wall. In spite of its small size, it is able to filter several quarts of water per hour, filtering out plankton and other organic particles and leaving the water much clearer than it might otherwise be.

TUNICATES AND LANCELETS SUBPHYLUM TUNICATA

SUBPHYLUM TUNICATA

Colonial Sea Squirt

Star Sea Squirt

Atrolium robustum

Botryllus schlosseri

HEIGHT

WIDTH (CLUSTER)

Up to 11/4 in (3 cm)

Up to 6 in (15 cm)

DEPTH

DEPTH

Shallow water

Shore and shallows

HABITAT

HABITAT

Coral reefs and rocks

Rock, stones, seaweeds

DISTRIBUTION Widespread in tropical reef waters of Indian and western Pacific Oceans

Coastal Arctic and temperate waters of north Atlantic

DISTRIBUTION

Individual star sea squirts are only about 3/32 in (2 mm) long and cannot live on their own. Instead, they arrange themselves in star-shaped clusters, or colonies, embedded in a shared gelatinous casing, called a tunic or test. At the center of each star is a shared outgoing (exhalent) opening through which used water is voided. The colonies vary greatly in color and may be green, violet, brown, or yellow, with the individuals having a contrasting color to the test.

Salp Pegea confoederata LENGTH

Up to 6 in (15 cm) DEPTH

Near surface HABITAT

Open water DISTRIBUTION

Warm waters worldwide

Salps are tunicates that resemble floating sea squirts. They swim by jet propulsion, taking in water through a siphon at one end of their bodies and expelling it at the other. Their transparent casing is loose and flabby and is encircled by four main muscles that form two distinct cross-bands. Individual salps are joined together in chains up to 12 in (30 cm) long, produced by the asexual reproduction (budding) of a young individual. The chains break up and disperse as they mature. Salps also reproduce sexually. Eggs are kept inside the body on the wall of the exhalent siphon, through which the developed larvae are expelled after being fertilized by sperm drawn in through the inhalent siphon.

SUBPHYLUM TUNICATA

Giant Pyrosome Pyrostremma spinosum Up to 33 ft (10 m) long DEPTH

Near surface HABITAT

Open water Warm waters between about 40˚ north and 40˚ south DISTRIBUTION

Pyura spinifera HEIGHT

Up to 12 in (30 cm) DEPTH

15–200 ft (5–60 m) HABITAT

Rocky reefs DISTRIBUTION

Temperate waters of Australia

The individuals that make up this giant, floating, colonial tunicate are only about 1 in (2 cm) long, but the colony, which resembles a gigantic hollow tube, can be large enough for a person to fit inside. Each individual lies embedded in the wall of the tube, with one end drawing in nutrientladen water from outside and the other end expelling water and waste inside. The expelled water is used to propel the colony as a whole. A wave of bioluminescent light travels along the community if it is touched.

SUBPHYLUM CEPHALOCHORDATA

Lancelet

Oikopleura labradoriensis

Branchiostoma lanceolatum

LENGTH

LENGTH

About 1/4 in (5 mm)

Up to 21/2 in (6 cm)

DEPTH

DEPTH

Near surface

Shore and shallows

HABITAT

HABITAT

Open water

Coarse sand

DISTRIBUTION Cold waters of north Atlantic, north Pacific, and Arctic

DISTRIBUTION Coastal temperate waters of northeastern Atlantic, and Mediterranean

Appendicularians are shaped like tiny tadpoles and live inside flimsy mucus dwellings that they build to trap plankton. Water enters the dwelling via two inlets covered by protective grids, passes through fine nets that trap any plankton in mucus, and passes out through an aperture. The animal eats the plankton-loaded mucus and beats its tail to create water currents.

Looking like a thin, semitransparent, elongate leaf, the lancelet is difficult to spot in the coarse sediments in which it lives. It usually lies half-buried in the sand with its head end sticking out. Muscle blocks that run along both sides of its body show through the skin as a pattern of V-shaped stripes. At the head end, a delicate hood ringed by stiff tentacles overhangs the mouth. This feature filters out large sediment particles but allows smaller, organic particles to pass so that they can be ingested.

filtering nets catch plankton

OCEAN LIFE

LENGTH

Sea Tulip

Appendicularian

excurrent siphon

SUBPHYLUM TUNICATA

SUBPHYLUM TUNICATA

This giant sea squirt is held up into the water on the end of a long, thin stalk. This means that its large inhalent siphon is in a better position to pull in plankton-rich water. The sea tulip’s body is covered in warty outgrowths and is naturally a bright yellow. However, the growth of an encrusting commensal sponge on many of these sea squirts gives them a pink appearance. During rough weather, sea tulips are often battered down onto the seabed, but they soon spring back on their flexible stalks.

Although it appears to be a solitary sea squirt, this species lives in urn-shaped colonies that share a single exhalent siphon (an opening through which water exits). The colony is dotted all over with the inhalent, or ingoing, siphons of the tiny zooids—the individuals that make up the colony. The colony’s green color results from the presence of the symbiotic cyanobacterium Prochloron.

SUBPHYLUM TUNICATA

319

320

ANIMAL LIFE

Jawless Fishes JAWLESS FISH FORM AN ANCIENT

group of vertebrates encompassing a diverse range of extinct groups. Today, KINGDOM Animalia there are only two small groups: the lampreys and the PHYLUM Chordata hagfish. They are considered to be the most primitive CLASSES Myxini living vertebrates, although many scientists do not Cephalaspidomorphi regard hagfish as true vertebrates. Hagfish and SPECIES 125 lampreys look similar, with elongated bodies and jawless mouths, but the two groups evolved along separate lines. Lampreys live in temperate coastal waters throughout the world and swim up rivers to breed, although some remain in fresh water. Hagfish are exclusively marine. DOMAIN Eucarya

Anatomy LAMPREY MOUTH At first glance, lampreys and hagfish could easily be mistaken for eels The oral disk, or sucker, of due to their long, thin bodies and slimy, scaleless skin. However, they lampreys is studded with horny lack a bony skeleton, and have only a simple flexible rod called a teeth arranged in roughly notochord running along the length of the body. In lampreys, the concentric rows. Larger teeth mouth is in the center of a round oral disk armed with small, rasping surround the central mouth opening. teeth. Hagfish have a slitlike mouth surrounded by fleshy barbels on the outside and by tooth plates on the dorsal fin gill openings inside. The gills in both groups open to the outside through small, BODY SECTION The bodies of lampreys (left) and hagfish are round pores behind the head, supported by a simple notochord flexed by a and there is a single nostril series of muscle blocks along the back. With notochord round, spinal cord on top of the head. no true bony vertebrae, this makes their fleshy mouth

HAGFISH

Hagfish find their way and detect carrion using fleshy barbels around the mouth. Their eyes are undeveloped and hidden beneath the skin, so they are nearly blind.

bodies very flexible. They have a tail and dorsal fin, but lack paired fins.

Reproduction Lampreys migrate from the sea into rivers and move upstream to spawn. In gravel, females lay thousands of tiny white eggs, which hatch into wormlike larvae called ammocoetes. These simple creatures have a horseshoeshaped mouth without teeth. They live in muddy tunnels for about three years, feeding on debris, then transform into adults and swim out to sea. Hagfish lay a few large eggs on the sea bed, and these hatch into miniature adults.

HAGFISH EGGS

The eggs of hagfish are armed with tiny anchor-like hooks at both ends. When laid, they stick together like a string of sausages.

OCEAN LIFE

Feeding With the exception of a few freshwater species, lampreys are parasitic, feeding on both bony and cartilaginous fish. They attach to their living host using the teeth and lips of their oral disk to suck onto their victim. Teeth in the mouth are then used to rasp a hole in the fish, and its flesh, blood, and body fluids are all consumed. Sometimes, lampreys cause the death of their host through blood loss or tissue damage. In contrast, hagfish are mostly scavengers that feed on dead fish and whale carcasses, as well as live invertebrates. They can gain leverage to tear off chunks of flesh by literally tying themselves in a knot and using the knot to brace themselves against the carcass. SHARK HOST

Large, slow-moving basking sharks are often parasitized by sea lampreys. The lampreys drop off when they have had their fill, leaving wounds that may get infected.

321 CLASS CEPHALASPIDOMORPHI

Sea Lamprey Petromyzon marinus LENGTH

Up to 4 ft (1.2 m) WEIGHT

Up to 51/2 lb (2.5 kg) DEPTH

3–2,100 ft (1–650 m) Coastal temperate waters of, and rivers adjacent to, north Atlantic DISTRIBUTION

With its long, cylindrical body, the sea lamprey might at first be mistaken for an eel, but closer inspection reveals differences. Unlike eels, the sea lamprey has no jaws. Its body is flattened toward the tail and it has two dorsal fins. Its circular mouth lies beneath the head, and is surrounded by a frill of tiny skin extensions. Inside the mouth, the teeth are arranged in numerous concentric arcs, which helps to distinguish it from the similar, but smaller, lampern (right). As a mature adult, the sea lamprey has dark

mottling on its back. Adults live at sea and feed on dead or netted fish as well as attacking a wide variety of live ones. It uses a “sucker” to attach to its host, scrapes a hole through the skin, and sucks out flesh and fluids. It spawns in rivers and the larvae remain in fresh water for about five years before they mature and move out to sea. This species is now rare as a result of trapping, intentional poisoning, and the degradation of its river habitat. CLASS CEPHALASPIDOMORPHI

Lampern Lampetra fluviatilis LENGTH

Up to 20 in (50 cm) WEIGHT

Up to 5 oz (150 g) DEPTH

0–30 ft (0–10 m) DISTRIBUTION Coastal waters and rivers of northeastern Atlantic, northwestern Mediterranean

The lampern is also known as the river lamprey because the adults never stray far from the coast and often remain in estuaries. It may be distinguished from the sea lamprey (left) by its smaller size, uniform color, and the smaller number and different arrangement of its teeth. Larvae that hatch in rivers migrate to estuaries, where they spend a year or so feeding on herring, sprat, and flounder.

CLASS MYXINI

Hagfish Myxine glutinosa LENGTH

Up to 30 in

(80 cm) WEIGHT

Up to 13/4 lb

(750 g) 130–4,000 ft (40–1,200 m)

DEPTH

DISTRIBUTION Coastal and shelf waters, below 55°F (13°C) in north Atlantic and western Mediterranean

This extraordinary fish can literally tie itself in knots and it does so regularly as a means of ridding itself of excess slime. Special slime-exuding pores run along both sides of the eel-like body, enabling it to produce sufficient slime to fill a bucket in a matter of minutes. The glutinous slime is usually more than adequate to deter most predators. Like all jawless fish, the hagfish has no bony skeleton but simply a supporting flexible rod of cells,

called a notochord, allowing it great flexibility. Fleshy barbels surround its slitlike, jawless mouth, and it has only rudimentary eyes. There is a single pair of ventral gill openings about a third of the way along the body. The hagfish spends most of its time buried in mud with only the tip of the head showing. It mainly eats crustaceans but will scavenge on whale and fish carcasses. Once the hagfish has latched onto a carcass with its mouth, it forms a knot near its tail, then slides the knot forward in order to provide itself with sufficient leverage to tear its mouth away along with a chunk of food.

CLASS MYXINI

Pacific Hagfish Eptatretus stoutii LENGTH

and feeds mainly on carrion. It causes great damage to fish caught in static nets and will enter large fish through either the mouth or the anus and proceed to eat them from the inside out, consuming their guts and muscles.

Up to 20 in (50 cm) WEIGHT

Up to 3 lb (1.4 kg)

dorsal finfold

DEPTH

65–2,100 ft (20–650 m) DISTRIBUTION Coastal and shelf waters of northeastern Pacific

The Pacific hagfish is similar to the hagfish found in the Atlantic. It is usually a brownish red color and may have a blue or purple sheen. It has no true fins, only a dorsal finfold that continues around the tail but that has little function in swimming. The Pacific hagfish lives in soft mud

CLASS MYXINI

Japanese Hagfish Eptatretus burgeri

WEIGHT

Insufficient information DEPTH

30–900 ft (10–270 m) DISTRIBUTION Inshore temperate waters of northwestern Pacific

OCEAN LIFE

LENGTH

Up to 24 in (60 cm)

This species is also known as the inshore hagfish because it lives in relatively shallow water compared to other species of hagfish. It is similar in shape and size to the Pacific hagfish, with six gill apertures and a white line along its back. It lives buried in mud close to shore but migrates to deeper water to breed. Unlike other species of hagfish, it reproduces seasonally; this is thought to be a response to changing temperatures in the shallow waters in which it lives. Its tough skin is used to make leather.

322

ANIMAL LIFE

Sharks, Rays, and Chimaeras CHIMAERAS are often informally grouped together as cartilaginous fish as they all have similar flexible KINGDOM Animalia skeletons. Within the group are some of Earth’s most efficient PHYLUM Chordata predators, such as the white shark, as well as filter feeders, such CLASS Elasmobranchii as the manta way. Some have features unusual for fish, such as SUBCLASSES 2 large brains, live birth, and warm blood. Fossils show that SPECIES 1,290 cartilaginous fishes have changed little in form in hundreds of millions of years. All have a skeleton of cartilage, teeth that are replaced by new ones when necessary, and toothlike scales covering their skin. snout DOMAIN Eucarya

SHARKS, RAYS, AND

mouth

Anatomy

nostril

pectoral fin gill slits

The internal skeleton of all the fishes in this group is made from flexible cartilage. In some species, parts of the skull and skeleton are strengthened by mineral deposits. The teeth are covered by very hard enamel and are formidable weapons. Sharks have several rows of teeth lying flat behind the active ones. These gradually move forward, and individual teeth may be replaced as often as every 8–15 days. Cartilaginous fishes have extremely tough skin. It is extra-thick in female sharks because males use their teeth to hold pelvic fin onto them when mating. A shark’s skin is covered in tiny, backwardcloaca pointing, toothlike structures called dermal denticles, which feel like sandpaper. Rays have scattered denticles, some enlarged to form spines, tail while chimaeras mostly have no denticles. Unlike bony fishes (see pp.338–41), cartilaginous fishes do not have a first dorsal fin gas-filled swim bladder. Sharks living in the open ocean, however, often have a very large, oil-filled liver, which aids buoyancy. gill slit

eye

pelvic fin

SHARK BODY SHAPE

A typical shark has a sleek, streamlined body. Most sharks have a tail that is asymmetrical (heterocercal), and thethe paired pelvic fins are set far back. The mouth is underslung, and there are five gill slits on each side. daggerlike point grips flesh

OCEAN LIFE

SANDTIGER SHARK

underslung mouth pectoral fin

heterocercal tail

serrated, bladelike edge cuts like a knife

TIGER SHARK palate, covered with flat teeth, crushes food

RAY

TOOTH ADAPTATIONS

Sharks’ teeth are shaped to suit their diet. Pointed ones are used for holding, while serrated teeth slice chunks from prey. Rays and chimaeras have teeth like grindstones to crush hard crustaceans and mollusks.

SHARK FISHING Sharks are heavily fished all over the world for their meat, fins, liver oil, and skin. They reproduce very slowly, producing only a few young every one to two years, and many species take a decade or more to reach full maturity. This slow rate of both reproduction and growth means that shark populations cannot sustain heavy fishing pressure, and take many years to recover. Worldwide, most stocks are currently being fished at rates above safe biological limits.

RAY BODY SHAPE

Skates and rays have flat bodies and large pectoral fins. The mouth is on the underside, so water for breathing is sucked in through a pair of holes, called spiracles, on the upper side, then passed over the gills.

second dorsal fin

anal fin

HUMAN IMPACT

SHARK FINS

Thousands of sharks are killed every year for their valuable fins, which are dried and then made into shark-fin soup. The body is often discarded while the shark is still alive.

CARTILAGINOUS FISH CLASSIFICATION

Reproduction In all cartilaginous fishes, the eggs are fertilized inside the female’s body. Adult males have organs on the belly called claspers—rodlike appendages derived from the pelvic fins. During mating, one or both claspers are inserted into the female’s cloaca (the shared opening of the digestive and reproductive tracts) to introduce the sperm. In sharks, mating can be a rough affair, although there may be some courtship. Chimaeras, as well as some sharks and rays, lay CATSHARK EGGS eggs—that is, they are oviparous. The eggs are These egg capsules protected by individual leathery egg capsules, often contain catshark known as mermaid’s purses. The young then hatch embryos, which will out several months later. In contrast, most sharks and hatch after about rays are viviparous: they give birth to live young after a year. The tendrils anchor the capsules a long period of gestation. In some species, the eggs to seaweeds. simply remain inside the mother until they hatch, sustained by yolk prior to birth (aplacental yolk sac viviparity). In about 10 percent of sharks, the young develop attached to a placenta-like structure and are directly nourished by the female’s body (placental viviparity). In all cases, the young are born fully formed, and they are able to hunt and feed. Immediately after birth, the female swims away and the young are left to fend for themselves. LEMON SHARK BIRTH

Lemon sharks move to shallow, sheltered bays or lagoons to give birth. The young emerge tail first and swim away. The mothers then leave the nursery grounds.

Sharks and rays are classified together in one class (the Elasmobranchii), while chimaeras, which include ratfish and rabbitfish, are placed in their own class (Holocephali). Sharks comprise nine orders and rays four orders. Chimaeras have one order, the Chimaeriformes. CHIMAERAS Order Chimaeriformes

spiracles. They have large pectoral and pelvic fins, two small dorsal fins, but no anal fin. Reproduction is yolk sac viviparity.

About 49 species

Chimaeras have a long, flabby body without scales, a large head with sensory canals, plate-like teeth, and one gill opening. The first of two dorsal fins is erectile with a venomous spine. Reproduction is oviparous. FRILL AND COW SHARKS Order Hexanchiformes 6 species

These sharks have a long, thin body, six or seven pairs of gill slits, small spiracles, and a single dorsal fin near the tail. Frill sharks have three-pointed teeth; cow sharks’ teeth are saw-like. Reproduction is yolk sac viviparity. SLEEPER AND DOGFISH SHARKS Order Squaliformes Six families form this large, varied order: bramble, dogfish, rough, lantern, sleeper, gulper, and kitefin sharks. All have spiracles, five gill slits, and two dorsal fins, but no anal fin. They have yolk sac viviparity. BRAMBLE SHARKS Order Echinorhiniformes Large, slow-moving deepwater sharks with thorn-like skin denticles. They have yolk sac viviparity.

The broad head of this shark provides space for extra electrical sense organs on the snout and gives a wide field of view, making it a formidable hunter.

BULLHEAD AND HORN SHARKS Order Heterodontiformes 9 species

Small, bottom-living sharks, these species have pointed front teeth and molar-like back teeth, a blunt, sloping head, nostrils connected to the mouth by a groove, paddlelike pectoral fins, an anal fin, and two spined dorsal fins. They are oviparous. CARPETSHARKS Order Orectolobiformes 42 species

These mainly bottom-living sharks include wobbegongs and nurse sharks. They have a broad, flattened head, barbels, and nostrils joined to the mouth by a deep groove. They have an anal fin and two spineless dorsal fins. Reproductive strategies vary.

130 species

2 species

HAMMERHEAD SHARK

323

MACKEREL SHARKS Order Lamniformes 15 species

These large sharks, which include the white, basking, and megamouth sharks, have a cylindrical body, conical head, two dorsal fins, an anal fin, and a long upper tail lobe. Many can maintain a high body temperature. They have yolk sac viviparity. GROUND SHARKS Order Carcharhiniformes At least 291 species

SAWSHARKS Order Pristiophoriformes 8 species

Small, slender sharks, these species have a flattened head and saw-like snout with barbels. They have two spineless dorsal fins, no anal fin, and have yolk sac viviparity.

Body shapes vary in this the largest and most diverse shark group. All species have two spineless dorsal fins and an anal fin. Reproductive strategies vary. RAYS AND SKATES Orders Rajiformes, Myliobatiformes, Pristiformes, Torpediniformes 718 species

ANGELSHARKS Order Squatiniformes About 20 species

These flattened, raylike sharks have a rounded head with gill slits on the side, and

These are mostly bottom-living fish with a flat, disk-shaped body, winglike pectoral fins joined to the head, and a long, thin tail. Reproduction is mostly viviparous with many live young, but some are oviparous.

Hunting Senses

AMPULLAE OF LORENZINI

BARBELS

The black spots on a shark’s snout are tiny electrical sense organs that help it find prey even in complete darkness.

Active at night, nurse sharks can find buried prey by touch and smell, using their sensory barbels.

OCEAN LIFE

Cartilaginous fishes have acute senses that help them to find prey, even if it is distant or buried in sediment. Predatory sharks smell or taste tiny amounts of blood as water passes over highly sensitive membranes in their nostrils, while catsharks also use smell to recognize each other. All cartilaginous fish have a system of pores called ampullae of Lorenzini that allows them to detect weak electrical signals given off by other animals. Most also have a lateral-line system, similar to that of bony fishes, which detects water movements. Cartilaginous fishes have eyes similar to those of mammals, and most have acute vision. They have no eyelids, but some sharks have a transparent “nictitating membrane,” which protects their eyes when they are attacking prey.

324 ORDER CHIMAERIFORMES

Pacific Spookfish Rhinochimaera pacifica LENGTH

About 41/4 ft

(1.3 m), plus tail filament WEIGHT

Not recorded

1,100–4,900 ft (330–1,500 m)

DEPTH

DISTRIBUTION

Parts of Pacific and eastern Indian

Ocean

REPRODUCTIVE EMBRACE

ORDER CHIMAERIFORMES

Plownose Chimaera Callorhinchus milii LENGTH

Up to about 41/4 ft (1.3 m) WEIGHT

Not recorded DEPTH

At least 750 ft (230 m) DISTRIBUTION Temperate waters in the southwest Pacific, off southern Australia and along the east coast of South Island, New Zealand

The plownose chimaera is also known as the elephant fish due to its most distinctive feature, a long, fleshy snout. The plownose uses this bizarre appendage to snuffle through mud of the ocean floor in search of shellfish, which it crunches up using its plate-like teeth. A network of prominent sensory canals crisscrosses its head. In spring, these fish come inshore into estuaries and bays to breed, and lay their eggs in horny, yellow-brown capsules. This chimaera is fished commercially for food.

Mating underwater is a slippery business, so the male plownose chimaera has a retractable, clublike, spiny clasper on its head that helps it hang onto the female. The male transfers his sperm when he inserts his pelvic clasper into the female’s cloaca. retractable clasper

ORDER CHIMAERIFORMES

Rabbit Fish Chimaera monstrosa LENGTH WEIGHT

Up to 5 ft (1.5 m) Up to 51/2 lb

(2.5 kg) Typically 1,000–1,300 ft (300–400 m)

DEPTH

DISTRIBUTION

ORDER CHIMAERIFORMES

Spotted Ratfish Hydrolagus colliei LENGTH

Up to 31/4 ft

(1 m) WEIGHT

Not recorded

Close inshore to at least 2,950 ft (900 m) DEPTH

OCEAN LIFE

DISTRIBUTION

Northeastern Pacific

The scientific name of the spotted ratfish means “water rabbit,” and it is also called the blunt-nosed chimaera. It belongs to the same family as the rabbit fish (see right) and is similar in shape, but unlike its relative, it does not have an anal fin on the underside next to the tail. Its pattern of white spots on a dark background may provide camouflage in the same way as the

spots help to camouflage deer in a forest. The spotted ratfish uses its large pectoral fins to glide and flap its way over the seabed in search of its prey, which consists mainly of mollusks and crustaceans. Like other chimaeras, the female lays eggs, each one encased in a tadpole-shaped, protective capsule. The eggs are laid in the summer, two at a time, and are dropped onto the seabed. The spotted ratfish is not fished commercially, since it is not very palatable, although it is sometimes unintentionally caught in nets along with other fish. It is not popular with fishermen because it has the ability to inflict a nasty wound with its sharp dorsal spine and can also deliver a painful bite. The spotted ratfish is frequently encountered at night by scuba divers, its large eyes glowing green by flashlight.

Eastern Atlantic and Mediterranean

Beautifully patterned with wavy brown and white lines, the rabbit fish belongs to a family called Chimaeridae, whose members have rounded snouts, long, tapering bodies,

When scientists first hauled a Pacific spookfish up from the ocean depths, they were astonished by the sight of its enormously long, conical snout. The long, brownish body of this strangelooking fish tapers to a thin tail, so that the fish gives the impression of being pointed at both ends. The snout is whitish, flexible, and covered in sensory pores and canals. Living in the dark depths of the ocean where its small eyes are of at best limited use, the spookfish uses its snout to find food and sense objects around it. The beak-shaped mouth under the base of the snout contains pairs of black, platelike teeth. Its tail has only a small lower lobe, while the upper lobe consists of a row of fleshy tubercles. Like other chimaeras, the spookfish relies mainly on its pectoral fins for propulsion rather than using its tail as most species of fish do. A very similar species of spookfish is found in the Atlantic Ocean. and tails ending in a long, thin filament, giving rise to their alternative name of ratfishes. The long, sharp spine in front of the first dorsal fin of the rabbit fish is venomous and can inflict a serious wound. Unlike sharks but in common with all other chimaeras, the rabbit fish can raise and lower this fin. The second dorsal fin is low and long and almost reaches the tail fin. Rabbit fish swim sluggishly in small groups and feed mainly on seabed invertebrates using their paired, rabbitlike teeth. These fish are often caught by accident in shrimp nets in the North Sea.

SHARKS, RAYS, AND CHIMAERAS ORDER HEXANCHIFORMES

Frilled Shark Chlamydoselachus anguineus LENGTH

Up to 61/2 ft

(2 m) WEIGHT

Not recorded

Mostly 66–4,921 ft (20–1,500 m)

DEPTH

DISTRIBUTION

Worldwide but discontinuous

ORDER HEXANCHIFORMES

Sharpnose Sevengill Shark Heptranchias perlo LENGTH

Up to 41/2 ft

With its elongated, eel-like body and flattened head, the frilled shark bears little resemblance to other sharks. The most noticeable difference is that its mouth is at the front of its head instead of on the underside. In addition, while most modern sharks have five pairs of gill slits, the frilled shark has six, each with a frilled edge. Its small teeth are also unusual, each having three sharp points. Frilled sharks have been observed swimming with their mouths open, displaying their conspicuous white teeth, leading to the suspicion that the teeth act as a lure for prey. This shark lives near the seabed in deep water but

occasionally comes to the surface. It feeds on deep-water fish and squid. The male has two long claspers on the belly, which are used to transfer sperm to the female when mating. This species has yolk sac viviparity, meaning that the eggs hatch inside the mother, which then gives birth to live young. Up to 12 young are born as long as two years after fertilization. Trawlers fishing for other deepsea species often catch frilled sharks as by-catch. Because this species reproduces so infrequently, it is especially vulnerable, and is listed as Near Threatened on the IUCN Red List of endangered species.

species that have seven gill slits—more than any other living shark species. It lives in deep water and hunts squid, crustaceans, and fish near the seabed. Like the sixgill sharks (see above), it has comblike teeth.Young fish have black markings, which fade with age,

on the tip of the single dorsal fin and on the upper part of the tail. Females have yolk sac viviparity and give birth to 6–20 young at one time.The sharpnose sevengill shark is rarely seen alive and little is known of its feeding and breeding behavior, but it is lively

325

ORDER HEXANCHIFORMES

Bluntnose Sixgill Shark Hexanchus griseus LENGTH

Up to 18 ft

(5.5 m) Up to at least 1,300 lb (600 kg)

WEIGHT

Up to 8,202 ft (2,500 m)

DEPTH

DISTRIBUTION

Tropical and temperate waters

worldwide

This enormous deep-water shark is sometimes spotted by divers in shallow water at night, but its more usual haunt is rocky seamounts and mid-ocean ridges. Its thick-set, powerful body has one dorsal fin, a large mouth lined with comb-like teeth, and six gill slits. Its fins are soft and flexible, not rigid like those of most sharks. Fish, rays, squid, and bottom-living invertebrates are this shark’s typical prey, although larger adults sometimes also hunt for seals and cetaceans.

and aggressive on the rare occasions when it is captured. It is occasionally caught up as by-catch in trawl nets, and this may be contributing to a reduction in its numbers. It is listed as Near Threatened on the IUCN Red List of endangered species.

(1.4 m) WEIGHT

Not recorded

Up to 3,300 ft (1,000 m), typically 90–2,360 ft (27–720 m)

DEPTH

DISTRIBUTION Tropical and temperate waters worldwide, except northeastern Pacific

The sharpnose sevengill shark, as its name suggests, has a sharply pointed snout and is one of only two shark

ORDER SQUALIFORMES

Piked Dogfish Squalus acanthias LENGTH

Up to 5 ft (1.5 m)

WEIGHT

Up to 20 lb (9 kg)

DISTRIBUTION Worldwide, except tropics, North Pacific, and polar waters

Sharks are not normally shoaling fish, but piked dogfish aggregate into huge groups numbering thousands of individuals, often all of one sex and

OCEAN LIFE

Up to 4,800 ft (1,460 m), typically 0–2,000 ft (0–600 m) DEPTH

size. Also known as the spurdog or spiny dogfish, this sleek, dark gray shark has two dorsal fins, each with a sharp spine in front of it. Irregular white spots decorate its sides, especially in young fish, and it has a pointed snout and large oval eyes. It was once very common and was possibly the most abundant species of shark, but it is now threatened globally as a result of overfishing. These sharks do not begin to breed until they are 20 years old and may live to be 30 or so years old. They grow very slowly, and the young take up to two years to develop inside the mother. Some populations migrate thousands of miles seasonally in order to avoid very cold water.

326

ANIMAL LIFE ORDER SQUALIFORMES

ORDER SQUALIFORMES

Velvet Belly Lanternshark

Greenland Shark Somniosus microcephalus

Etmopterus spinax LENGTH

LENGTH

Up to 18 in

WEIGHT

(45 cm) WEIGHT

Up to 1,710 lb

(775 kg) Up to 2 lb (850 g)

0–8,694 ft (0–2,650 m)

DEPTH

Typically 650–1,650 ft (200–500 m), up to 8,200 ft (2,500 m) DEPTH

DISTRIBUTION

Up to 21 ft

(6.4 m)

DISTRIBUTION

North Atlantic and Arctic waters

The sluggish Greenland shark has a heavy, cylindrical body that is usually brown or gray. It has a short, rounded snout and two equal-sized dorsal fins. As well as feeding on a variety of live prey, including fish, sea birds, and seals, this shark is also a scavenger, often eating dead cetaceans and drowned land animals, such as reindeer. It is often caught by hook-and-line at ice holes while it hunts seals, but its flesh is poisonous and must be boiled several times before it becomes edible.

Eastern Atlantic and Mediterranean

As this small shark searches for fish and squid in the darkness, its black belly is illuminated by tiny, bright light organs called photophores. It has large eyes and two dorsal fins, each with a strong, grooved spine in front. It is one of about 30 similar species that include the smallest known sharks.

broad, interlocking teeth on lower jaw

ORDER SQUATINIFORMES

Pacific Angel Shark Squatina californica LENGTH

Up to 6 ft (1.8 m)

WEIGHT

Up to 60 lb

(27 kg) Typically 10– 1,000 ft (3–300 m), up to 656 ft (200 m) DEPTH

DISTRIBUTION

Continental shelf of the eastern

Pacific

Resembling something between a squashed shark and a ray, the Pacific angel shark spends most of its time lying quietly on the seabed. Its sandy or gray back, peppered with dark spots and scattered dark rings, provides good camouflage. Though superficially similar to a ray, this fish is marked out as a true shark by the gill slits on the side of its head, while rays have their

gills underneath. It draws water in through large, paired holes called spiracles behind its eyes and pumps it over the gills. Rearing up like a cobra, the Pacific angel shark ambushes passing fish including halibut, croakers, and other bottom-dwellers. It has also been known to snap at divers and fishermen who have provoked it. At night, it swims for short distances above the seabed, sculling along with its tail. Females give birth to litters of six to ten pups after a gestation of nine to ten months.Young fish do not mature until they are at least ten years old and can live until they are 35 years old. This fish used to be abundant in the waters off California until intense fishing caused a population collapse in the 1990s. A gill net ban ended the fishery. This shark is categorized as Near Threatened on the IUCN Red List of endangered species.

ORDER SQUALIFORMES

Cookiecutter Shark Isistius brasiliensis LENGTH

Up to 20 in

(50 cm) WEIGHT

Not recorded

0–11,500 ft (0–3,500 m)

DEPTH

DISTRIBUTION

Atlantic, Pacific, and southern

Indian Ocean

ORDER PRISTIOPHORIFORMES

Longnose Sawshark Pristiophorus cirratus LENGTH

Up to 5 ft

(1.5 m) WEIGHT

Not recorded

130–2,067 ft (40–630 m)

DEPTH

Temperate and subtropical waters of southern Australia

OCEAN LIFE

DISTRIBUTION

Many cetaceans and large fish, including other sharks, suffer when cookiecutter sharks are around. This small, cigar-shaped shark is a parasite that bites chunks out of its prey. Using its unique thick, flexible lips to hold onto its victim by suction, it then twists itself around so that its razor-sharp lower teeth bite out a cookie-shaped piece of flesh. It is active at night, luring its victims with glowing green bioluminescent lights on its belly. It also preys on squid and crustaceans. Like all sawsharks, this species has a head that is flattened and extended to form a long, saw-like projection, or rostrum. This is edged with rows of large, sharp teeth. Two long sensory barbels hang down from the underside of the rostrum, which is studded with further sense organs, and the shark uses these to detect vibrations and electrical fields. It seeks out and kills prey, such as fish and crustaceans, by poking around on the seabed and slashing out sideways with its rostrum.

SHARKS, RAYS, AND CHIMAERAS ORDER ORECTOLOBIFORMES

Tasseled Wobbegong Eucrossorhinus dasypogon At least 41/4 ft

LENGTH

(1.3 m) WEIGHT DEPTH

Not recorded

At least 130 ft

(40 m) DISTRIBUTION Southwestern Pacific off northern Australia and Papua New Guinea

eye on prominent ridge

While it lies still, the tasseled wobbegong looks like a seaweedcovered rock, which is exactly its objective. It is one of a group of flattened, bottom-living sharks that are masters of camouflage. The squashed shape and broad, paired fins are further adaptations to an existence on the ocean floor. This species has a beautiful reticulated pattern of narrow, dark lines against a paler background. Around its mouth is a fringe of skin flaps that resemble weeds. During the day, it rests unseen under overhangs

and ledges on coral reefs. At night, this highly successful ambush predator emerges onto the reef to find a good vantage point from which to snap up passing fish. There is no escape from the gape of its huge jaws and its needlelike teeth for any fish straying near, as the tasseled wobbegong lunges up and grabs its prey. This species has been reported to bite divers who disturb it. Little is yet known of its biology, and reef destruction and overfishing have reduced its numbers.

ORDER HETERODONTIFORMES

ORDER ORECTOLOBIFORMES

The tasseled wobbegong looks remarkably similar to the angler (see p.351), which is an unrelated species of bony fish. Both of these predators, which specialize in ambushing their prey, are flattened, have broad heads, wide mouths disguised by skin flaps, and sharp, pointed teeth. Following a similar lifestyle, these two species have come up with similar answers, an example of convergent evolution.

ORDER ORECTOLOBIFORMES

Zebra Shark

Tawny Nurse Shark

Heterodontus portusjacksoni

Stegostoma fasciatum

Nebrius ferrugineus

LENGTH

Up to

LENGTH

(1.7 m) WEIGHT

Up to 8 ft

(2.4 m) Not recorded

WEIGHT

0–900 ft (0–275 m) Temperate waters off southern Australia and possibly New Zealand

DISTRIBUTION

Up to 101/2 ft

Indian Ocean and southwestern

Pacific

The zebra shark is often seen by divers around coral reefs. Its long, ridged body and densely spotted skin make it unmistakable. Juveniles have stripes instead of spots and no ridges. This shark spends most of the day lying on the reef, usually facing into the current. At night, it squirms its flexible body into cracks and crevices on the reef, searching for mollusks, crustaceans, and small fish.

WEIGHT

Not recorded

3–230 ft (1–70 m), typically 16–100 ft (5–30 m)

DEPTH

DISTRIBUTION Indian Ocean, western and southwestern Pacific

The docile, bottom-living tawny nurse shark is a favorite with underwater photographers because, although it may bite if harassed, it can be approached closely. During the day, it rests quietly in caves and channels in coral reefs, emerging at night to hunt for invertebrates. A pair of long sensory barbels on either side of the mouth helps the shark to find its prey, which it crushes using wide teeth.

OCEAN LIFE

This small shark belongs to a group of about nine sluggish, bottom-living sharks called bullhead or horn sharks. It has two dorsal fins, each with a short spine, and large, paddlelike, paired fins. It is a poor swimmer and uses its fins to crawl over the seabed at night in search of sea urchins, which it grabs using its pointed front teeth and crushes using broad rear teeth. Females lay unusual spiral egg cases, which they wedge into crevices.

Not recorded

DEPTH

DISTRIBUTION

LENGTH

(3.2 m)

0–210 ft (0–63 m)

DEPTH

dorsal fin

MISLEADING SIMILARITY

Port Jackson Shark 51/2 ft

327

328

ORDER ORECTOLOBIFORMES

Whale Shark Rhincodon typus 40–65 ft (12–20 m) LENGTH

WEIGHT Over 13 tons (12 metric tons)

Surface, deep water in winter DEPTH

DISTRIBUTION

Tropical and temperate waters

worldwide

The whale shark is a graceful, slow-moving giant and the largest fish in the world. At 5 ft (1.5 m) wide, its mouth is large enough to fit a human

inside, but it is a harmless filter feeder that eats only plankton and small fish. To obtain the huge amount of food it needs, it sucks water into its mouth and pumps it out over its gills, where particles of food become trapped by bony projections called gill rakers and are later swallowed. This shark has the thickest skin of any animal, at up to 4 in (10 cm) thick. Prominent ridges

ORDER LAMNIFORMES

run the length of its body, and it has a large, sickle-shaped tail. The pattern of white spots on its back is unique to each fish, enabling scientists, through analysis of photographs, to identify individuals. While little is known of their ocean travels, satellite tagging has shown that some whale sharks migrate across entire oceans. Whale shark eggs hatch inside the mother, and she gives birth to live young. Whale sharks are killed for their meat and fins (used in soup), although they are legally protected in some countries.

ORDER LAMNIFORMES

Megamouth Shark

Sandtiger Shark

Megachasma pelagios

Carcharias taurus

At least 18 ft (5.5 m) LENGTH

WEIGHT

LENGTH

Not recorded

WEIGHT

DISTRIBUTION

Little known, but probably worldwide

This gigantic shark was discovered as recently as 1976, when one became entangled in the folds of a ship’s sea anchor. Like the whale shark and

ORDER LAMNIFORMES

Basking Shark Cetorhinus maximus LENGTH 20–36 ft (6–11 m)

OCEAN LIFE

WEIGHT Up to 7.7 tons (7 metric tons) DEPTH 3,937 ft (1,200 m) DISTRIBUTION Cold- to warm-temperate coastal waters worldwide

The world’s second-largest fish, the basking shark is protected in several countries. In summer, it swims open-mouthed at the surface, filtering out plankton. Every hour, the shark

Up to 350 lb

(160 kg)

0–540 ft (0–165 m) DEPTH

in the tropics

Up to 101/2 ft

(3.2 m)

DEPTH

basking shark, it is a filter feeder, gulping down huge mouthfuls of shrimp, which it probably compresses with its huge tongue. At night it follows the shrimp toward the surface and is thought to attract them with bioluminescent tissue inside its mouth. passes up to 395,000 gallons (1.5 million liters) of seawater through the huge gills that almost encircle its head. Its liver runs the length of the abdominal cavity and is filled with oil to aid buoyancy.

0–625 ft (0–190 m)

Warm-temperate and tropical coastal waters, except eastern Pacific

DISTRIBUTION

Also known as the ragged-tooth shark and the gray nurse shark, the sandtiger shark is fearsome to look at. It is heavily built and its daggerlike, menacing teeth protrude, even when its mouth is closed. Many people will have seen these sharks in aquariums,

FEASTING ON PLANKTON Every year, around April, whale sharks migrate to Ningaloo Reef off northwestern Australia for a plankton feast. The plankton explosion results from a simultaneous mass spawning of the reef ’s corals, possibly triggered by the full moon.

and they are quite docile in captivity despite their chilling appearance. The sandtiger shark has a flattened, conical snout, is light brown in color, and its body is often speckled with darker spots. It lives in shallow coastal waters, especially on reefs and in rough, rocky areas with gullies and caves. Although it spends most of its time near the sea floor, it can hover in mid-water by filling its stomach with air gulped in at the surface. The mother gives birth to two live young at a time, one from each of a pair of uteri every other year. Within each uterus there are many other embryos, and the strongest embryo in each uterus kills and eats its siblings along with any unfertilized eggs before it is born. Sandtiger sharks are widely hunted for both sport and food.

SHARKS, RAYS, AND CHIMAERAS ORDER LAMNIFORMES

HUMAN IMPACT

SHARK ATTACK

White Shark Carcharodon carcharias Up to about 20 ft (6 m)

LENGTH

Over 3.7 tons (3.4 metric tons)

WEIGHT

0–4,300 ft (0–1,300 m)

DEPTH

DISTRIBUTION Wide range through most oceans except polar waters

The white shark, or great white, is one of the most powerful predators in the ocean and has a reputation as a killing machine. In fact, this shark is intelligent and capable of complex social interactions. It is, however, first and foremost a predator, feeding on prey that ranges from small fish to tuna, marine mammals (such as porpoises, seals, and sea lions), and birds (such as gannets and penguins). Its powerful, tapered body and crescent-shaped tail are designed for sudden, swift attack, which may occur with such momentum that the shark leaves the water. It can sustain high speeds even in cold waters because it can maintain a body temperature well above that of the surrounding water due to adaptations in its circulatory system. This means that the shark’s metabolism is more efficient than that of other sharks, allowing it to swim faster and with greater endurance. Large numbers of these sharks are attracted to areas where there are sea mammal colonies, such as off South Africa. Satellite tags have shown that they can migrate huge distances. Their numbers are declining due to sport fishing, netting, and commercial bycatch.

The white shark has made more unprovoked attacks on humans than any other shark. However, humans are not its natural prey and many such attacks can be put down to the shark mistaking a diver for a seal or turtle. When stimulated by bait in the water, white sharks will bite anything, even a metal diving cage.

serrated edge

COUNTER-SHADED COLORATION

From above, the shark’s dark back merges with the seabed; from below, its white belly blends with the down-welling light.

FEARSOME TEETH

This shark’s teeth can be up to 3 in (7.5 cm) long. They are as hard as steel with razor-sharp, serrated edges that can slice through the toughest flesh.

ORDER LAMNIFORMES

ORDER CARCHARHINIFORMES

Goblin Shark

Chain Catshark

Mitsukurina owstoni

Scyliorhinus retifer

Up to 123/4 ft (3.9 m)

LENGTH

WEIGHT

329

LENGTH

2 ft (0.6 m)

Up to 460 lb

WEIGHT

(210 kg)

Not recorded

1,000–4,300 ft (300–1,300 m)

DEPTH 246–2,461 ft (75–750 m)

DEPTH

DISTRIBUTION Not fully known, but thought to be in temperate and tropical waters

Caribbean

this shark except that it gives birth to live young and after death changes from pinkish to a dirty, brownish gray color. Only a few dozen goblin sharks have officially been caught, and this species is thought to be rare. Most data has come from sharks caught by boats fishing for deep-water fish using long lines. Fossils of sharks very similar to this species have been found in rocks over 100 million years old.

North and western Atlantic,

OCEAN LIFE

One of the strangest-looking of all deep-water sharks, the goblin shark is pale pink, with a flabby body, tiny eyes, and a long, flattened, bill-like snout. This strange projection is covered in electroreceptors and is probably used to detect prey in the inky depths. Beneath the snout, the goblin shark has specialized jaws that can be shot forward to grab fish and octopuses using long, pointed teeth. Not very much else is known about

DISTRIBUTION

With its chain-link pattern, this shark (also known as the chain catfish) is unmistakable. It is one of about 160 catsharks that make up the largest shark family, Scyliorhinidae. Living on the seabed, it feeds on worms, crustaceans, and small fish. Deep furrows connect the nostrils to the mouth, and the eyes are catlike. Catsharks lay 40–50 eggs per year in horny capsules with long tendrils at each corner. The empty cases may be washed ashore and are known as mermaid’s purses.

WHITE SHARK

One of the world’s most formidable predators, the White Shark catches its prey with a short, fast attack, typically from below. Sometimes its speed takes it and its prey clear of the water. The shark then often withdraws to wait for its victim to weaken before returning to finish it off.

332 ORDER CARCHARHINIFORMES

Blue Shark Prionace glauca LENGTH

Up to 13 ft (4 m) WEIGHT

Up to 450 lb (200 kg) DEPTH

0–1,150 ft (0–350 m) Temperate and tropical waters worldwide

DISTRIBUTION

A true ocean wanderer, the blue shark makes seasonal trans-ocean crossings in search of food. It is streamlined and elegant, with a long, pointed snout, and characteristic white-rimmed black eyes. On long journeys, it may use its winglike pectoral fins to help it glide on ocean currents. On the way, it makes frequent, deep dives, possibly to help it get its magnetic bearings. When chasing fish, this shark may reach speeds of 43 mph (70 km/h). It has been known to harass swimmers and has caused a few human fatalities. Although one of the most common sharks, it is also the most exploited and its populations are declining.

ORDER CARCHARHINIFORMES

Scalloped Hammerhead Shark Sphyrna lewini LENGTH

Up to 14 ft (4.3 m) WEIGHT

Up to 330 lb (150 kg) DEPTH

0–3,230 ft (0–1,000 m) ORDER CARCHARHINIFORMES

Tiger Shark Galeocerdo cuvier LENGTH

Up to at least 18 ft (5.5 m) WEIGHT

Up to 1,750 lb (800 kg) DEPTH

0–459 ft (0–140 m) DISTRIBUTION

Tropical and warm temperate waters

worldwide

The tiger shark is the second most dangerous shark to humans, after the white shark (see p.331). It is huge and has a heavy head and a mouth filled

ORDER CARCHARHINIFORMES

Whitetip Reef Shark OCEAN LIFE

Triaenodon obesus LENGTH

Up to 61/2 ft (2 m)

WEIGHT

Up to 37 lb

(18 kg) DEPTH Typically 25–130 ft (8–40 m), recorded at 1,080 ft (330 m) DISTRIBUTION

and Pacific

Tropical waters of the Indian Ocean

with serrated teeth that have the characteristic shape of a cockscomb. One reason it is so dangerous is that it prefers coastal waters and is also found in river estuaries and harbors, and so it frequently comes into contact with humans. It is reputed to eat almost anything—as well as eating smaller sharks, including young tiger sharks, other fish, marine mammals, turtles, and birds, it is an inveterate scavenger, and a huge variety of garbage has been found in tiger shark stomachs. The young, born live after hatching from eggs inside the mother, begin life marked with blotches, which become “tiger stripes” in juveniles and fade by adulthood. One of the sharks most often seen by divers is the whitetip reef shark, which during the day may be found around coral reefs resting in caves and gullies, often in groups. The tip of its first dorsal fin and the upper tip of its tail are white, in contrast to its grayish brown back. At night, the whitetip comes out to hunt reef fish, octopus, lobsters, and crabs hidden among the coral. Packs sometimes hunt together, sniffing out the prey and bumping and banging the coral to get at them.

DISTRIBUTION

Tropical and warm temperate waters

worldwide

Along with the seven other known species of hammerhead sharks, the scalloped hammerhead has a strange, flattened, T-shaped head. In this

species, the front of the head has three notches, which produces the scalloped shape from which it takes its name. The eyes are located at the sides of the head. Hunting near the seabed, the shark swings its head from side to side, looking for prey such as fish, other sharks, octopus, and crustaceans, and using sensory pits on its head to detect the electrical fields of buried prey such as rays. The head may also function as an airfoil, giving the shark lift and helping it to twist and turn as it chases its prey. Scalloped hammerheads may be seen in large shoals of over a hundred individuals. They give birth to live young in shallow bays and estuaries, where the skin of the young darkens to give protection against sunlight.

SHARKS, RAYS, AND CHIMAERAS ORDER RAJIFORMES

Common Skate Dipturus batis LENGTH

Up to 91/2 ft

(3 m) WEIGHT

Up to 220 lb

(100 kg) DEPTH 330–3,300 ft (100–1,000 m) DISTRIBUTION Eastern Atlantic from northern Europe to southern Africa, Mediterranean

The common skate is the largest and heaviest of the European rays. Due to overexploitation, it is now a rare species throughout most of its range and has become extinct in some

ORDER RAJIFORMES

Atlantic Guitarfish Rhinobatos lentiginosus LENGTH

Up to 30 in (75 cm) WEIGHT

Not recorded DEPTH

0–100 ft (0–30 m) Coastal waters of Gulf of Mexico, Caribbean, and western Atlantic DISTRIBUTION

ORDER RAJIFORMES

Painted Ray Raja undulata LENGTH

Up to 4 ft (1.2 m) WEIGHT

Up to 15 lb (7 kg) DEPTH

150–650 ft (45–200 m) DISTRIBUTION

Eastern Atlantic and Mediterranean

regions. Its snout is long and pointed, and the front margin of the wings is strongly concave, giving this skate an overall angular shape. Its tail has a row of spines along its length but, unlike the large stinging spine of stingrays, these are not venomous. This species is sometimes called the blue skate because its underside is bluish gray. It can swim strongly and feeds on fish in mid-water as well as hunting over the seabed for crabs, lobsters, bottom-dwelling fish, and other rays. Its oblong egg cases are up to 10 in (25 cm) long. They are laid in fall or winter and hatch two to five months later. While mature specimens prefer deeper water, the young will spend time in shallow waters.

Guitarfish are elongated rays with a triangular snout and narrow pectoral fins. Like sharks, these rays use their spineless tails for swimming, while other rays swim by flapping only their pectoral fins. The Atlantic guitarfish has two small dorsal fins set far back near the tip of its tail. Grayish brown with small white spots, it blends in with the sandy seabed, but this ray can be seen in shallow water searching for mollusks and crabs, probing the sand with its snout. Females have placental viviparity, giving birth to about six live young. Also known as the undulate ray, the painted ray is one of the most distinctive northern European rays. This species is patterned with long, wavy, dark lines edged with white spots that run parallel to the wing margins. Its ornate appearance makes it an attractive species for aquariums, but in its natural habitat, this pattern has the practical advantage of helping the ray to blend in with the gravel and sand on the seabed, where it feeds on flatfish, crabs, and other bottom-living invertebrates. The biology of this beautiful ray has not been fully studied, but during the breeding season, males use paired claspers to transfer sperm during mating, and females are known to lay up to 15 eggs in muddy or sandy flats. Each egg is encased in a reddishbrown, oblong egg capsule up to 3½ in (9 cm) long, with a curved horn at each corner. Additional information on the distribution and status of this and other rays around Britain is currently being collected through an egg-case identification project. Members of the public are encouraged to collect empty egg cases that have been washed ashore, rehydrate them, and identify them. The number and location of egg cases found are collated each year. dorsal fin

ORDER RAJIFORMES

Reticulate Whipray Himantura uarnak LENGTH About 15 ft (4.5 m) including tail WEIGHT

About 265 lb

(120 kg) DEPTH 65–165 ft (20–50 m) DISTRIBUTION Coastal waters of Arabian Gulf, Red Sea, Indian Ocean, and western Pacific

This beautifully patterned stingray belongs to a group called whiprays, which have long, thin, flexible tails. Its upper surface is densely covered with wavy brown lines or reticulations. Its disk, or body, is about 5 ft (1.5 m) long and the tail can be nearly three times this length. Its stinger is a single, large spine located a short distance from the tail base; some individuals have two spines. The body is almost diamond-shaped and the snout is broadly triangular with a pointed tip. Found in warm waters, mainly near the coast, reticulate whiprays are sometimes seen by divers, lying quietly in sandy patches between rocks.

ORDER PRISTOFORMES

Smalltooth Sawfish Pristis pectinata LENGTH

Up to 25 ft (7.6 m) WEIGHT

Up to 770 lb (350 kg) DEPTH

0–33 ft (0–10 m) DISTRIBUTION

Subtropical waters in all oceans

Sawfish are elongated rays with a long, flat, sawlike snout, or rostrum, which they use to slash through shoals of fish and dig for shellfish and invertebrates. Like all rays, they have gill slits on the underside of the body rather than the sides. Females give birth to live young, which are about 2 ft (60 cm) long in the smalltooth species. The saws of the pups are sheathed and flexible at birth, in order to prevent injury to the mother. The smalltooth sawfish lives in coastal waters but also swims up river estuaries. Numbers of this species are severely depleted and it is listed as Critically Endangered on the IUCN Red List of endangered species.

OCEAN LIFE

pelvic fin

333

334

ORDER MYLIOBATIFORMES

Southern Stingray Dasyatis americana WIDTH (WINGSPAN)

61/2 ft (2 m) WEIGHT

Up to 300 lb (135 kg) DEPTH

0–180 ft (0–55 m) DISTRIBUTION

Western Atlantic, Gulf of Mexico,

Caribbean Sea

Stingrays are feared because their long tails are equipped with one or more daggerlike, venomous spines. The southern stingray has a single, serrated spine about midway along the tail and a flap of skin, also known as a finfold, on the underside of the tail. Its thick disk is dark gray on top and white underneath. This stingray spends most of the day lying buried in the sand at the bottom of shallow lagoons and off beaches. At night, the ray feeds by excavating holes in the sand and crunching up bivalve mollusks,

crustaceans, and worms. Because its eyes are on top of its head, it cannot see its prey but uses smell and electro-receptors to detect it. While it is buried, its spiracles—through which it draws in water for breathing—are visible as a pair of holes in the sand. People are often stung when they inadvertently step on southern stingrays; the stinging spine is sharp enough to cause a serious wound and the venom causes severe pain. The pain can be reduced by immersing the wound in hot water.

ORDER RAJIFORMES

Manta Ray Manta birostris WIDTH (WINGSPAN)

Up

to 26 ft (8 m) Up to 4,000 lb (1.8 metric tons)

WEIGHT

0–80 ft (0–24 m); usually near surface

DEPTH

Surface tropical waters worldwide, sometimes warm temperate areas

DISTRIBUTION

ORDER MYLIOBATIFORMES

Round Stingray Urolophus halleri LENGTH

23 in (58 cm) including tail WEIGHT

3 lb (1.4 kg) DEPTH

0–300 ft (0–90 m)

OCEAN LIFE

DISTRIBUTION

Eastern Pacific

As its name suggests, the Round Stingray has an almost circular disk. This species and its relatives the “stingarees” have shorter tails than other stingrays and the tail ends in a leaf-shaped fin. The Round Stingray varies in color from pale to dark brown and can be either plain or mottled with darker spots and reticulations. These rays are most often seen in summer, when they move

inshore into inlets and bays to forage for invertebrates among seagrass and bask in the warm-water shallows. Females arrive in the shallows around June ready to breed, and the males, who are already there, swim along the shoreline looking for suitable mates. Sexually mature females are reported to give off an electrical field that the males can sense. Females give birth about three months after mating to about six live young. The juveniles stay inshore, where there are fewer predators, until they mature. When out foraging, they do not stray too far, remaining within an area of about 1 square mile (2.5 square km). Predators of the Round Stingray include the Northern Elephant Seal and the Black Sea Bass. They are also likely to be hunted by large carnivorous fish such as sharks. The Round Stingray’s sting is painful and can cause minor injuries.

Divers often describe the experience of swimming beneath a manta ray as like being overtaken by a huge flying saucer. This ray is the biggest in the world, but like the biggest shark, the whale shark, it is a harmless consumer of plankton and small fish. When feeding, it swims along with its cavernous mouth wide open, beating

its huge triangular wings slowly up and down. On either side of the mouth, which is at the front of the head instead of on the underside as in other rays, are two long lobes, called cephalic horns, that funnel plankton into the mouth. These are the origin of its other name of Devil Ray. A short, sticklike tail trails behind. On coral reefs, manta rays tend to congregate over high points where currents bring plankton up to them. Small fish called remoras often travel attached to these giants. Despite their huge size, these rays can leap clear of the water, occasionally giving birth to their young as they do so. The Manta ray is also sociable with divers in some sites, and has been known to “dance” with them.

335

HUMAN IMPACT

STINGRAY CITY Southern stingrays are not aggressive toward humans and only sting if stepped on or feel threatened. Their stings are used as defense against sharks, their natural predator. At a site in Grand Cayman in the Caribbean, called “Stingray City,” they have become used to humans and can be hand-fed.Visitors wade, swim, and dive among these graceful creatures.

ORDER MYLIOBATIFORMES

ORDER TORPEDINIFORMES

Blue-spotted Stingray

Atlantic Torpedo Torpedo nobiliana

Taeniura lymma

LENGTH Nearly 61/2 ft (2 m) including tail

Up to 61/2 ft (2 m) including tail

LENGTH

WEIGHT

WEIGHT

Up to 65 lb

DEPTH

(30 kg) Shallow water to about 65 ft (20 m)

DISTRIBUTION

Indian Ocean, western Pacific,

Red Sea

Since it is active in the daytime, divers often see this beautifully colored ray on coral reefs. It is most often spotted lying on sandy patches under coral heads and rocks. Often, its blue-striped tail sticks out and gives away its hiding place. Large, bright blue spots cover the disk, which is greenish brown. Like all stingrays, it has a venomous spine on its tail. As the tide rises, these rays move in groups into shallow water to hunt for invertebrates such as mollusks, crabs, shrimp, and worms.

To 2,600 ft

(800 m)

DEPTH

DISTRIBUTION

Up to 200 lb

(90 kg)

ORDER MYLIOBATIFORMES

Spotted Eagle Ray Aetobatus narinari WIDTH (WINGSPAN)

Up to 10 ft (3 m) WEIGHT

Up to 500 lb (230 kg) DEPTH

DISTRIBUTION

Tropical waters worldwide

Often solitary, spotted eagle rays also move around in huge shoals of at least a hundred individuals in open waters—a truly spectacular sight when silhouetted against a sunlit surface. Unlike most other rays, the spotted eagle ray is a very active swimmer.

Electric rays use special organs to produce electricity, which they discharge to stun their prey or attack predators. The Atlantic torpedo is the largest electric ray and can produce a shock of up to 220 volts—enough to stun a person. It can easily be recognized by its circular, disklike body and short, thick tail ending in a large, paddle-shaped fin. It is a uniform dark brown or black on the back and white underneath. The electric organs are in the ray’s wings, or pectoral fins, and like a battery, they can store electricity. When hunting, the Atlantic torpedo wraps its wings around its prey before stunning it.

OCEAN LIFE

3–260 ft (1–80 m)

Most of its swimming time is spent in open water, although it is also commonly seen inshore. It appears to “fly” through the water as it moves its pointed “wings”—enlarged pectoral fins—gracefully up and down. Besides the beautiful patterning of spots on its dorsal surface, another distinctive feature of the spotted eagle ray is its head, which ends in a flattened, slightly upturned snout that resembles a duck’s bill. It has a long, thin whiplike tail with a venomous spine near the base. These rays are very agile and can twist and turn to escape predatory sharks. Sometimes, small groups splash around at the surface, making spectacular leaps out of the water. Why they do this is not clear, but it may be to help dislodge parasites.

Atlantic, Mediterranean

336

ANIMAL LIFE

Bony Fishes BONY FISHES EXCEED ALL OTHER VERTEBRATE

groups both in number of living species and in their abundance. They have KINGDOM Animalia evolved into myriad shapes and sizes, suiting every aquatic PHYLUM Chordata lifestyle and habitat and range from the shore to the deepest CLASSES Actinopterygii depths and from polar seas to hot deep-sea vents. Bony fishes Sarcopterygii have an internal skeleton of bone, although that of a few ORDERS 48 primitive groups is part cartilage. The bony skeleton supports SPECIES 31,290 flexible fins that allow them to move with far greater precision than do the stiff fins of cartilaginous fishes. About one-third of bony fishes live only in fresh water, while the remainder lives in the oceans or migrates between the two. DOMAIN Eucarya

Like other vertebrate animals, bony fishes have a skull, backbone, and ribs, but the skeleton also extends out into the fins as a series of flexible rays. Bony fishes, unlike sharks, can use their paired pectoral and pelvic fins for maneuvering, braking, and even swimming backward. Spiny-rayed fishes, a group that includes most bony fishes, also have sharp spines in the front portion of their dorsal, anal, and pelvic fins. A bony flap called the operculum covers the gills of bony fishes. It SWIMMING can be opened to regulate the flow of water in The sideways force and backward force exerted when a fish moves its through the mouth and out over the gills. A tail from side to side results in a covering of overlapping, flexible scales made thrust at an angle between the two. of thin bone protects most bony fishes. Some The resultant thrusts on left and right primitive bony fishes, such as sturgeon, are produce a net backward thrust and so the fish is propelled forward. armored with thick, inflexible scales or plates.

Many important bony fish stocks are fished at unsustainable levels. Relieving the pressure by fish farming is not easy as species such as cod are difficult to rear on a large scale. In contrast, almost all Atlantic salmon come from aquaculture. Many farmed fish eat feed prepared from other wild-caught fish.

SALMON FARM

Salmon farms, such as this one in Tasmania, are a common sight in temperate seas. However, there are problems with fish lice (see p.346) and with dilution of the wild gene pool by escapees.

movement of tail sideways force

BONY SKELETON

Flexible rays and hard spines support all the fins in bony fish, such as this cod. The fins connect to spines extending from the vertebrae. The fish can precisely adjust the position of each fin.

first dorsal fin vertebrae linked into a flexible vertebral column spine extends from vertebra to fin second dorsal fin

skull

third dorsal fin

orbit (eye socket)

rib pectoral fin bony gill covering (operculum)

first anal fin

second anal fin

pelvic fin

esophagus gill filaments

tail (caudal) fin surface concealed under adjacent scale

oral valve

annual growth ring

mouth

exposed surface

exposed surfaces overlap to create smooth covering

direction of water movement

OCEAN LIFE

FISH FARMING

forward movement

Anatomy

hinged jaw

HUMAN IMPACT

gill arch, attachment point for filaments

GILLS, VIEWED FROM ABOVE

SCALES

As water passes over the gill filaments, gases are exchanged. Oxygen passes into the blood and carbon dioxide passes out into the water. Within the filaments, the blood flows in reverse relative to the water outside, so the concentration of gases in the fluids is opposed, which speeds the gases’ transfer.

Bony fishes can be aged by their scales. Slow winter growth produces dark rings on the scales, so each dark ring indicates one year of life. The system works best for temperate-water fish such as cod.

resultant thrust backward force

BONY FISHES gas gland

intestine

rete mirabile

dorsal aorta swim bladder

SWIM-BLADDER FUNCTION

A bony fish regulates its buoyancy by secreting gas, usually oxygen, from a gas gland into its swim bladder. The gland is supplied with blood (the source of the gas) by a network of capillaries called a rete mirabile.

Buoyancy

337

brightly colored

second dorsal fin Most bony fishes have a gas-filled swim bladder that allows them to adjust their buoyancy, enabling them to hover in midwater and keep from sinking. This is especially useful to fish that spend their lives in midwater. Many bottom-living fish, such as flatfish, have a poorly developed swim bladder or none at all. To compensate for pressure changes as a fish swims toward or away from the surface, it regulates the amount of gas in the swim bladder, usually by secreting gas into it through a gland. In some primitive fish, such as the herring, the swim bladder is connected to the gut and is filled when the fish gulps air at the surface. Many bony fishes can vibrate the swim bladder with special muscles to anal fin produce sounds. Cartilaginous fishes do not have a swim bladder. They gain MULTIPURPOSE FINS buoyancy to some extent with their large, oil-filled livers and lightweight Triggerfish swim by undulating their bones. However, cartilaginous fishes must also use their large pectoral fins second dorsal and anal fins, maintaining and tail to give them lift. Bony fishes with a swim bladder have been freed buoyancy with their swim bladder. Bright from this necessity and, in many species, the fins have developed into fins may also function as visual signals versatile appendages used for courtship, feeding, attack, or defense. in communication, including courtship.

FLEXIBLE APPENDAGES

A frogfish displays one of the many functions of bony fish fins. Since they are not required to give the fish lift, the warty frogfish’s paired fins have evolved into flexible appendages with which it clambers over the sea bed.

Senses Bony fishes use vision, hearing, touch, taste, and smell.Vision is most important in well-lit habitats. Coral reef fish have good color vision, and they use colors and patterns for recognition, warning, deception, and courtship. Color receptors in the eyes do not operate well in dim light. Nocturnal fish and fish living in the twilight zone (see p.170) have large, sensitive eyes, but little sensitivity to different colors. Dark-zone fish often have only tiny eyes, but have a sharp sense of smell and use pheromones for long-distance communication. Sound also carries well underwater (see p.37) and some fish produce intense sounds with their swim bladder. Bony fishes move in unison in shoals with the help of their lateral-line sensory system, for which there is no equivalent in other vertebrates. Sense organs arranged in a canal along the head and sides of each fish pick up water movements created by the other fish. The wide field of view, due to having eyes set on the sides of the head, also helps precision shoaling. SIGNALLING COLORS

Color is effective in communication on well-lit coral reefs. The gaudiness of the Mandarin Fish may warn predators that it is unpalatable.

LATERAL LINE

OCEAN LIFE

The lateral-line system can be seen in many bony fishes, such as the pollack shown here, as a white line along the sides of the fish. The shape of the line is a useful identification feature.

338

ANIMAL LIFE

Reproduction The majority of bony fish, when mature, simply shed their eggs and sperm directly into the sea, where fertilization takes place. The eggs develop and the larvae hatch while drifting on ocean currents. Death rates of eggs and larvae are high, so many eggs are laid—up to 100 million by the giant ocean sunfish. Once the larvae have grown to juvenile fish, they often congregate in nursery grounds in sheltered estuaries and bays. In contrast to most oceanic fish, many coastal bottom-living species are able to protect their offspring, so they lay fewer, larger eggs, often hiding them or caring for them until they hatch. Some have evolved elaborate forms of care, such as mouth brooding.

MOUTH BROODING

When a female jawfish has laid her eggs, the male collects them into his mouth to keep them safe. He will not feed until the eggs hatch and the fry disperse.

SEX CHANGE IN THE CUCKOO WRASSE

1

Like most wrasse, cuckoo wrasse have a complex reproductive pattern featuring sex change. The majority of eggs develop first into pink females.

Some older females develop the blue-and-orange pattern of males and change sex after about seven years of age. Others remain female.

2

At the next spawning season, a sex-changed male acquires vibrant colors and courts all females in his territory, fertilizing their eggs (see p.369).

3

Hunting and Protection

OCEAN LIFE

All fish must eat and in doing so may expose themselves to the risk of being eaten if they come out into the open to forage. Their ultimate aim is to survive long enough to reproduce successfully and so pass on their genes to the next generation. Bony fish have evolved many ingenious methods for catching prey and defending themselves against predators. Camouflage is an effective strategy and can serve to hide a fish, both from its predators and from its prey. Color patterns can also deceive, and butterflyfish use false eye patterns to fool predators into lunging for their tail end. In the CAMOUFLAGE crowded environment of a coral reef, many Scorpionfish employ color, shape, and behavior in a small fish protect themselves with spines. Filefish combined camouflage erect a dorsal spine and lock it into position, strategy. Experts at keeping thereby preventing larger fish from swallowing still, they can strike with them. Out in the surface waters of the open lightning speed if a small ocean, there is nowhere to hide, and many fish strays within reach. small fish live in shoals for safety. Predators find it difficult to pick out a target as the shoal moves and swirls. Although the shoal is conspicuous, it is safer for each individual to join than to swim alone.

SHOALING

Even predatory fish need protection from larger predators, especially when young. Barracuda juveniles live in shoals during the day, while most adults hunt alone.

SHADOW-HUNTING

Trumpetfish often shadow predatory fish when they hunt, since the larger fish will often flush out suitable prey. This trumpetfish has chosen to swim with a Nassau grouper similar in color to itself.

BONY FISHES

339

BONY FISHES CLASSIFICATION Bony fish comprise the ray-finned fishes (class Actinopterygii), and the lobe-finned fishes (class Sarcopterygii), including the lungfishes (freshwater) and the coelacanths, but also giving rise to tetrapods (see cladogram, p.206). Below are 30 marine orders of both classes. COELACANTHS Order Coelacanthiformes

CATFISH Order Siluriformes

2 species

3,604 species

One family—the only marine lobe-finned fish. Fins arise from fleshy, limblike lobes, vertebral column not fully formed.

Only two marine families out of 33. Long body, up to four pairs of barbels around mouth. Sharp, sometimes venomous spine in front of dorsal and pectoral fins. Most with adipose fin.

STURGEONS AND PADDLEFISH Order Acipenseriformes 28 species

SMELTS Order Osmeriformes

Only sturgeon family is marine. Skeleton part bone, part cartilage. Sturgeons have asymmetrical tail and underslung mouth.

321 species

TARPONS AND TENPOUNDERS Order Elopiformes

SALMONS Order Salmoniformes

9 species

219 species

Two families, mostly marine. Spindle-shaped, silvery fish, one dorsal fin, forked tail. Unique bones in throat (gular plates). Swim bladder can be used as lung. Transparent larvae.

One family with marine, anadromous, and freshwater members. Powerful, spindleshaped fish, with large mouth and eyes. One fin plus adipose fin on back. Small, rounded scales. Pelvic fins abdominal.

BONEFISH Order Albuliformes 13 species

One family, mostly marine. Similar to tarpons, but smaller and very bony, with complex structural differences.

MORAY EEL, ORDER ANGUILLIFORMES

EELS Order Anguilliformes 908 species

Marine and freshwater, 16 families. Body long and thin, no scales or pelvic fins, one long fin along back, tail, and belly. SWALLOWERS AND GULPERS Order Saccopharyngiformes 28 species

Four families of highly aberrant deep-sea, eel-like fish with huge, loose jaws; no tail fin, pelvic fins, scales, ribs, or swim bladder.

Thirteen families, mostly marine or anadromous. Small, slim relations of salmon.

DORIES AND ALLIES Order Zeiformes

610 species

33 species

Ten families, mostly marine and benthic. Most with two or three spineless dorsal fins and a chin barbel. Grenadiers have long, thin tails.

Six families, all marine. Deep-bodied but thin fish; large, spiny head and protrusile jaws. Long dorsal and anal fins with spines at front.

TOADFISH Order Batrachoidiformes 83 species

One family, mostly marine, coastal, and benthic. Broad, flat head, wide mouth, eyes on top; one short, spiny and one long, soft dorsal fin. CUSK EELS Order Ophidiiformes 531 species

Five families, mostly marine. Eel-like fish with long dorsal and anal fin that may join with tail fin. Thin pelvic fins. ANGLERFISH, ORDER LOPHIIFORMES

ANGLERFISH Order Lophiiformes

263 species

358 species

Sixteen families, all marine. Diverse, slim coastal and deep-sea fish. Large mouth with many small teeth. Pelvic fins abdominal, one fin plus adipose fin on back, no fin spines.

Eighteen families, all marine. Large, flattened or rounded head with cavernous mouth and fishing lure on top. Shallow-water species benthic; deep-water species pelagic.

LANTERNFISH Order Myctophiformes

CLINGFISH Order Gobiesociformes

252 species

162 species

Seven families, all marine. Colorful, bright, often huge, open-water fish with crimson fins. Many have long rays from dorsal fin.

TURBOT, ORDER PLEURONECTIFORMES

FLATFISH Order Pleuronectiformes

SILVERSIDES Order Antheriniformes

Seven families, all marine. Deep-bodied, big eyes (except deep-water), dorsal fin spiny at front, forked tail, large scales. Most nocturnal.

796 species

Eleven families, mostly marine. Lie on seabed. Body flattened from side to side, both eyes on upper side. Start life as normal, symmetrical fish larvae in plankton. PUFFERS AND FILEFISH Order Tetraodontiformes 437 species

Ten families, marine and freshwater. Very diverse group ranges from triggerfish to ocean sunfish. Small mouth with few large teeth or tooth plates. Scales usually modified as plates, spines, or shields.

OCEAN LIFE

HERRING, ORDER CLUPEIFORMES

164 families, marine and freshwater. Largest and most diverse vertebrate order. Most have both spines and soft rays in dorsal and anal fins. Pelvic fins close to pectorals and with one spine. Perciform classification subject to change.

Six families, marine and freshwater. Mostly long, thin fish with jaws extended as beaks. Flying fish have large pectoral and pelvic fins.

161 species

37 species

11,061 species

266 species

SQUIRRELFISH AND RELATIVES Order Beryciformes

MILKFISH Order Gonorynchiformes

Five families, marine and freshwater. Long body encased in armor of bony plates. Small mouth at end of tubular snout.

NEEDLEFISH Order Beloniformes

Ten families, marine and freshwater. Small, slim, silvery fish; most with two dorsal fins, often in large shoals.

Seven families, mostly marine. Silvery body with keeled belly and forked tail. Anchovies and herring comprise two biggest families.

364 species

One family, mostly marine. Small, shallowwater, benthic fish; pelvic fins forming sucker-disk. Eyes set high; single dorsal fin.

344 species

399 species

PIPEFISH AND SEAHORSES Order Syngnathiformes

PERCHLIKE FISH Order Perciformes

GRINNERS Order Aulopiformes

25 species

Five families, mostly freshwater. Long, thin, stiff with bony scutes along sides, separate spines on back. Seamoths aberrant, flattened with enlarged pectoral fins.

1,649 species

Four abundant, deep-ocean families. Mostly elongate predators with large teeth and photophores. Significant part of ocean’s fishes.

VELIFERS, TUBE-EYES, AND RIBBONFISH Order Lampriformes

29 species

Thirty-six families, mostly marine. Mainly shallow water, benthic. Large, spiny head, most with spiny dorsal fins, often venomous. Unique bony strut across cheek.

426 species

Two deep-ocean, widely distributed, abundant families. Small, slim fish, large eyes and mouth. One fin plus adipose fin on back. Many photophores. Daily vertical migration.

STICKLEBACKS AND SEAMOTHS Order Gasterosteiformes

SCORPIONFISH AND FLATHEADS Order Scorpaeniformes

LIGHTFISH, DRAGONFISH, AND HATCHETFISH Order Stomiiformes

HERRINGS Order Clupeiformes

Four families, only milkfish and beaked salmon marine. Pelvic fins set far back.

COD FISH Order Gadiformes

340

ANIMAL LIFE ORDER COELACANTHIFORMES

Coelacanth Latimeria chalumnae LENGTH

Up to 6 ft (2 m)

WEIGHT

Up to 210 lb

(95 kg) DEPTH 490–2,300 ft (150–700 m) DISTRIBUTION

Western Indian Ocean

When it was first discovered in 1938, the coelacanth was nicknamed “old four legs” because its pectoral fins had strange, fleshy, limblike bases. The only other primitive group to have a similar arrangement are the freshwater lungfish. It is from fish like these that the first four-legged land animals are thought to have developed. This coelacanth’s tail has an extra small

ORDER ACIPENSERIFORMES

European Sturgeon Acipenser sturio LENGTH

11 ft (3.5 m)

WEIGHT Up to 880 lb (400 kg) DEPTH 13–295 ft (4–90 m)

OCEAN LIFE

DISTRIBUTION Coastal waters of northeastern Atlantic, Mediterranean, and Black Sea

Like most sturgeon, this species swims from the sea into large rivers to spawn in gravelly areas. These prehistoric-looking fish belong to a primitive group in which only the skull and some fin supports are made of bone. The rest of the skeleton consists mainly of cartilage. Instead of scales, five rows of distinctive bony plates, or scutes, run along the body. Two pairs of barbels hang down from flattened, bony head barbels

lobe in the middle, and its body is covered in heavy scales, which are made up of four layers of bone and a hard mineral material. In life, these shimmer an iridescent blue with white flecks. Coelacanths live in deep water on steep, rocky reefs and, so far, have been found at only a few sites off the south and east coasts of Africa and the west coast of Madagascar. By using small submersibles to study these fish, scientists have discovered that they retreat into caves at night. When out searching for food, they drift along in ocean currents or scull slowly with their fins. Having located a fish or squid, the coelacanth then uses its powerful tail to propel itself forward so that it can seize its prey. The coelacanth is listed as Critically Endangered on the IUCN Red List of Endangered Species. International trade in this species is banned.

ORDER COELACANTHIFORMES

DISCOVERY

FOSSIL EVIDENCE Coelacanths were thought to have become extinct about 65 million years ago. When a live coelacanth was caught in 1938, comparing it with fossil coelacanths enabled scientists to confirm its identity. A living specimen of a fossil group had been found.

Indonesian Coelacanth Latimeria menadoensis LENGTH

Up to 41/2 ft

(1.4 m) WEIGHT

Up to 200 lb

(90 kg) 490–655 ft (150–200 m)

DEPTH

Celebes Sea, north of Sulawesi, in the western Pacific

DISTRIBUTION

FOSSIL COELACANTH

Fossil specimens of coelacanths have features almost identical to present-day coelacanths, including the unique three-lobed tail.

When the Indonesian coelacanth was discovered in 1998, it was at first thought to be the same species as the one found in African waters (see left). The two are indeed very similar, but molecular studies suggest that they are different species. An entire ocean separates them, and because coelacanths are slow swimmers, the populations are not thought to mix. The Indonesian coelacanth has the same white markings and distinctive gold flecks as the African species, but it is brown rather than bluish. As yet, little is known of its life history, but because it is so physically similar to the African species, it probably has the same behavior and could therefore be endangered by fishing.

HUMAN IMPACT

CAVIAR BAN Once common, the European sturgeon is now extremely rare due to overfishing and poaching, and because locks and polluted estuaries have made many rivers unsuitable for spawning. Few active spawning sites remain. This sturgeon is critically endangered, and international trade in the fish itself and any products from it, including caviar (salted roe), has been banned.

ORDER ACIPENSERIFORMES

Beluga Sturgeon Huso huso LENGTH

the pointed snout and are used to search out bottom-living invertebrates. The European sturgeon is thought to live for at least 60 years. bony scute

16 ft (5 m)

Up to 4,400 lb (2,000 kg)

WEIGHT

230–590 ft (70–180 m)

DEPTH

Northern Mediterranean, Black Sea, Caspian Sea, and associated rivers

DISTRIBUTION

The beluga is both the largest species of sturgeon and the largest European fish to enter fresh water. Stouter and heavier than the European sturgeon (see left), it has a more triangular snout with a very wide mouth. Four long barbels hang from the underside of the snout, reaching almost to the mouth. Like all sturgeon, the beluga has an asymmetrical, sharklike tail with the backbone extending into the large upper lobe. Reputed to be the most expensive fish in the world, it also produces the most prized caviar, with large fish containing 220–440 lb (100–200 kg). The beluga sturgeon is endangered due to poaching and damming of its spawning rivers.

341

ORDER ELOPIFORMES

Tarpon Megalops atlanticus LENGTH

Up to 8 ft (2.5 m) WEIGHT

350 lb (160 kg) DEPTH

0–100 ft (0–30 m) Coastal waters of western and eastern Atlantic DISTRIBUTION

ORDER ELOPIFORMES

Ladyfish

With its large scales and intensely silvery body, the tarpon resembles an oversized herring but, in fact, is closely related to the eels. It has an upturned mouth, and the base of the single dorsal fin is drawn out into a long filament, although this is not always easy to see. Living close inshore, this fish often enters estuaries, lagoons, and rivers. If it enters stagnant water, it surfaces and gulps air, which passes from the esophagus into its swim bladder; this then acts like a lung.

Tarpon spawn mostly in open water at sea. A large female can produce over 12 million eggs, but larval and juvenile mortality is high. The larvae, which are thin and transparent and very like eel larvae except that they have forked tails, drift inshore into estuarine nursery grounds. Tarpon larvae are also found in pools and lakes that become temporarily cut off from the sea. Fishermen get to know the areas where tarpon shoals can regularly be seen from year to year, hunting for

other shoaling fish such as sardines, anchovies, and mullet. They will also eat some bottom-living invertebrates such as crabs. Considered an excellent game fish in US and Caribbean waters, tarpon make spectacular leaps when hooked. They are also fished commercially and, in spite of being rather bony, are considered delicious. Tarpon can live for 55 years and are often displayed in public aquariums. Their large scales are sometimes used in ornamental work.

ORDER ALBULIFORMES

Bonefish

Elops saurus

Albula vulpes LENGTH

LENGTH

Up to 3 ft (1 m)

Up to 3 ft (1 m)

WEIGHT

WEIGHT

22 lb (10 kg)

22 lb (10 kg)

DEPTH

DEPTH

0–165 ft (0–50 m)

0–280 ft (0–85 m) DISTRIBUTION

Tropical and subtropical coastal waters of western and eastern Atlantic

The ladyfish has a single dorsal fin in the middle of its back and a tail that is deeply forked. Shoals of this slim, silvery blue fish can be found close to the shore and will skip along the surface if alarmed by a boat’s engine noise. The adult fish move offshore to spawn in open water, and the young larvae, which resemble eel larvae, eventually drift back into sheltered bays and lagoons. Also known as the ten-pounder, the ladyfish is considered a good game fish and will leap out of the water when hooked. It is fished commercially, but it is not a very high-quality food fish and so is often used for bait.

As its common name suggests, this fish is extremely bony. It is streamlined and silvery, with dark markings on its back, a single dorsal fin, and a blunt snout extending over the mouth. Bonefish have been found in tropical and subtropical waters of the Pacific Ocean, but it is not yet known if these populations are a different species from those found in the eastern and western Atlantic. Although bonefish do not make good eating, they are one of the world’s most important game fish. Fishermen enjoy stalking them through the shallows in bays and estuaries as they often swim at the surface with the dorsal fin showing.

OCEAN LIFE

DISTRIBUTION Coastal waters of western Atlantic and Caribbean Sea

342

ANIMAL LIFE ORDER ANGUILLIFORMES

ORDER ANGUILLIFORMES

European Eel

Chain Moray Eel

Anguilla anguilla

Echidna catenata LENGTH

Up to 41/4 ft

LENGTH

Up to 51/2 ft (1.7 m)

(1.3 m) WEIGHT

14 lb (6.6 kg)

WEIGHT

Not recorded

0–2,300 ft (0–700 m) DEPTH

DEPTH

0–40 ft (0–12 m) DISTRIBUTION Temperate waters of northeastern Atlantic, fresh water inland

Living most of its life in fresh water, the European eel swims thousands of miles down to the sea and across the Atlantic Ocean to the Sargasso Sea to spawn. After spawning in deep water, the eels die, leaving the eggs to hatch into transparent, leaflike (leptocephalus) larvae. Over the next year or so, the larvae drift back to the coasts of Europe. Nearing the coast, they change shape and become tiny transparent eels, or elvers, that swim and wriggle their way up rivers into fresh water. The European eel is becoming increasingly scarce due to pressure on stocks caused by fishing and the damming of rivers.

DISTRIBUTION

VERSATILE HUNTER Most species of moray eels spend the day in holes in a reef with just their heads sticking out, emerging at dusk to hunt. They rely on their excellent sense of smell to find fish resting between corals and rocks. Unusually, the chain moray eel also hunts over rocky shores and

reefs at low tide during the day. It uses its sharp eyesight to search for fish and crustaceans in crevices and holes and, when it has located its prey, it strikes, rather like a snake. Other moray eels will sometimes strike at passing prey from their holes during the day.

Tropical reefs of western and central

Atlantic

The chain moray eel is one of very few marine eels that can survive for some time out of water, and it will forage over wet rocks for up to 30 minutes at a time during low tide. As long as it remains wet, it can absorb some oxygen through its skin. The chain moray eel is easily recognized by its short, blunt snout and chainlike yellow markings. Some of its teeth are broad and molarlike and help it to cope with heavily armored prey such as crabs. It can swallow small crabs whole, but breaks up bigger ones first by twisting, tugging, and thrashing around. The chain moray eel is a member of a large family of moray eels (Muraenidae) that live on reefs throughout the tropics. Most species of moray eels are nocturnal, but the chain moray eel is usually active during the day.

short, blunt snout

broad teeth

ORDER ANGUILLIFORMES

ORDER ANGUILLIFORMES

Slender Snipe Eel

Ribbon Eel

Nemichthys scolopaceus

Rhinomuraena quaesita LENGTH

Up to

41/4

ft

LENGTH

WEIGHT

Not recorded

WEIGHT DEPTH

Tropical reefs of Indian and Pacific

DISTRIBUTION

Temperate and tropical seas

oceans

worldwide

Unlike most other eels, ribbon eels change color and sex during their life. Juveniles are nearly black with a yellow dorsal fin. As they mature, the black becomes bright blue and the snout and lower jaw turn yellow. This is the male color stage. When they reach a body length of about 41/4 ft (1.3 m), the males turn yellow and become fully functional females, which lay eggs. Ribbon eels live on coral reefs, mostly hiding in crevices. They have leaflike nostril flaps, which sense vibrations in the water.

This long, slender, deep-sea eel has remarkable jaws, shaped like a bird’s bill, with the ends turned out so that they can never fully close. It spends its life drifting in midwater, catching small crustaceans to eat. When the males mature and are ready to spawn, their jaws shorten, they lose all their teeth, and their front nostrils grow into large tubes. This probably enhances their sense of smell, helping them to find mature females. Little else is known of the slender snipe eel’s lifestyle, as it is rarely caught.

ORDER ANGUILLIFORMES

Conger Eel Conger conger LENGTH

Up to 10 ft (3 m) WEIGHT

Up to 240 lb (110 kg) DEPTH

1,600 ft (0–500 m)

OCEAN LIFE

Not recorded

300–6,600 ft (90–2,000 m)

3–200 ft (1–60 m) DEPTH

DISTRIBUTION

Up to 41/4 ft

(1.3 m)

(1.3 m)

Temperate waters of northeastern Atlantic and Mediterranean DISTRIBUTION

The large, gray head of a conger eel sticking out of a hole in a shipwreck is a familiar sight to many divers. Like their relatives the moray eels, conger eels hide in holes and crevices in rocky reefs during the day, only emerging at night to hunt for fish, crustaceans, and

cuttlefish. This snakelike fish has a powerful body with smooth skin, no scales, and a pointed tail. A single dorsal fin runs along the back, starting a short distance behind the head, continuing around the tail, and ending halfway along the belly. In the summer, adult conger eels migrate into deep water in the Mediterranean and Atlantic to spawn and then die. The female lays 3–8 million eggs, which hatch into long, thin larvae that slowly drift back inshore, where they grow into juvenile eels. They take 5–15 years to reach sexual maturity. The conger eel is a good food fish and is caught in large numbers by anglers, but it sometimes manages to use its strength to escape with the bait.

BONY FISHES ORDER ANGUILLIFORMES

Spotted Garden Eel Heteroconger hassi LENGTH

Up to 16 in (40 cm) WEIGHT

Not recorded DEPTH

23–150 ft (7–45 m) Red Sea and tropical waters of Indian Ocean and western Pacific DISTRIBUTION

These eels spend their lives swaying gracefully to and fro with their heads up in the water and their tails in their sandy burrows. Several hundred fish live together in a colony, or “garden,” looking like evenly spaced plants blowing in the breeze. Garden eels are much slimmer than their close relatives, the conger eels. They are only about 1/2 in (14 mm) in diameter and have very small pectoral fins. The spotted garden eel usually has two large dark spots behind the head as well as many tiny ones all over the

body. It has an upturned mouth that is designed to pick tiny planktonic animals from the water as the current flows by. Colonies of these eels occur only on sandy slopes that are exposed to currents but sheltered from waves. When danger threatens, the eels sink back down into their burrows, using their tails as an anchor until only their small heads and eyes are visible. They are very difficult to photograph

hard, pointed tail tip

Banded Snake Eel Myrichthys colubrinus LENGTH

Up to 38 in (97 cm) WEIGHT

Not recorded DEPTH

Shallow water Tropical waters of Indian Ocean and western Pacific DISTRIBUTION

tiny eyes

wide mouth

ORDER SACCOPHARYNGIFORMES

Gulper Eel Saccopharynx lavenbergi LENGTH

Up to 5 ft (1.5 m) WEIGHT

Not recorded DEPTH 6,600–9,800 ft (2,000–3,000 m) DISTRIBUTION Deep waters of eastern Pacific, from California to Peru

The gulper eel is best known for its ability to swallow prey as large as itself. This fish has a small head and tiny eyes but enormous jaws. Its mouth and throat can be hugely distended to engulf its prey and the teeth can be depressed backward. Its stomach can be similarly extended to accommodate its gargantuan meals. The body ends in a luminous organ on a long, whiplike tail. This feature may be used as a lure or a decoy; this has yet to be confirmed, since no one has been able to observe these deep-sea fish in the wild. The gulper eel has planktonic eggs that develop into long, thin larvae, like those of its shallow-water relatives, and it probably dies after spawning.

OCEAN LIFE

Cleverly disguised to look like the venomous yellow-lipped sea krait, the banded snake eel is avoided by most predators. This allows it to hunt safely over sand flats and seagrass beds near coral reefs for small fish and crustaceans. Most individuals of this species are banded with broad black and white bands, but in some areas these eels have dark blotches between the bands. This color variant may

eventually be identified as a different species. The banded snake eel has a pointed head with a pair of large tubular nostrils on the upper jaw that point downwards. This arrangement gives the fish an excellent sense of smell that allows it to seek out prey hidden beneath the sand surface. With only tiny pectoral and long dorsal fins, the banded snake eel swims by undulating its long body. When not hunting, it buries itself in the sand using the hard, pointed tip of its tail to burrow in tail-first. These fish are most active by night. They tend to remain in their burrows during the day and so are not often seen by divers. The banded snake eel belongs to a large family (Ophichthidae) which includes around 250 snake and worm eels, most of which burrow into sand and mud. All the members of this family have flattened transparent, leaflike (leptocephalus) larvae.

underwater because they are able to detect the vibrations from a scuba diver’s air bubbles and will disappear when they are approached. Spotted garden eels stay in their burrows even when spawning. Neighboring males and females reach across and entwine their bodies before releasing eggs and sperm. Mixed colonies of spotted and whitespotted garden eels sometimes occur.

long, slender tail

distinctive banded markings

ORDER ANGUILLIFORMES

343

344 ORDER CLUPEIFORMES

Atlantic Herring Clupea harengus LENGTH

Up to 18 in (45 cm) WEIGHT

Up to 21/4 lb (1 kg) DEPTH

0–650 ft (0–200 m) DISTRIBUTION

North Atlantic, North Sea, and

Baltic Sea

Until the middle of the 20th century, the Atlantic herring was the mainstay of many fishing communities bordering the North Sea and north

ORDER CLUPEIFORMES

Peruvian Anchoveta Engraulis ringens LENGTH

Up to 8 in (20 cm) WEIGHT

Up to 1 oz (25 g) DEPTH

10–260 ft (3–80 m) DISTRIBUTION West coast of South America and southeastern Pacific

The distribution of this tiny, silvery relative of the herring depends on the yearly extent of the Peruvian Current. This cold, deep current comes to the surface along the west coast of South America, bringing rich supplies of nutrients with it. Enormous shoals of anchoveta feed on the plankton blooms triggered by the increase in nutrients. The fish shoal within about 50 miles (80 km) of the coast, and many local people depend on them, as do many birds, including pelicans.

ORDER CLUPEIFORMES

South American Pilchard Sardinops sagax LENGTH

Up to 16 in (40 cm) WEIGHT

Up to 171/2 oz (485 g) DEPTH

0–650 ft (0–200 m) DISTRIBUTION West coast of South America and southeastern Pacific

Enormous shoals of these fish, made up of millions of individuals, were once found, but excessive fishing has reduced their numbers greatly.

ORDER CLUPEIFORMES

Allis Shad Alosa alosa LENGTH

Up to 33 in (83 cm) WEIGHT

Up to 9 lb (4 kg) DEPTH

0–16 ft (0–5 m)

OCEAN LIFE

DISTRIBUTION Temperate waters of northeastern Atlantic and Mediterranean Sea

Pilchards are an important food fish and are also used to produce oil and fish meal. The South American pilchard may, in fact, be the same species as the California pilchard, and, worldwide, all pilchard species are very similar. These silvery, medium-sized fish are blue-green on the back and have a series of black marks along the sides. The Allis shad is a silvery fish belonging to the herring family (Clupeidae) and is one of the few that enter fresh water. During April and May, mature adults migrate into rivers to spawn, swimming up to 500 miles (800 km) upstream. In some parts of its range, the species is known as the May fish. Its streamlined body is covered by large circular scales that form a keel under the belly, and it has a single dorsal fin. It is now very rare over much of its range.

ORDER GONORYNCHIFORMES

Milkfish Chanos chanos LENGTH

Up to 6 ft (1.8 m) WEIGHT

Up to 31 lb (14 kg) DEPTH

0–100 ft (0–30 m) Tropical and subtropical waters of Indian and Pacific oceans

DISTRIBUTION

Atlantic. Along the East Anglian coast of Great Britain, the fish were known as silver darlings. In the 20th century, excessive fishing using new techniques led to a steep decline in stocks. Today, the stocks are managed, but they are still under pressure. The Atlantic herring feeds on plankton, coming to the surface at night after spending the day in deeper water. It lives in large shoals, and across its range the species is divided into distinct local races, which differ from each other in size and behavior. Each race has several traditional spawning grounds. The females produce up to 40,000 eggs each, which form a thick mat on the seabed. The milkfish is an elegant silvery fish with a streamlined body and a large, deeply forked tail. It is an important food fish in much of Southeast Asia and is extensively farmed. It feeds on plankton, soft algae, cyanobacteria, and small invertebrates. It is easy to keep in captivity as it is able to tolerate a wide range of salinity. Mature fish spawn in the sea, and the eggs and larvae drift inshore. Juveniles swim into estuaries and mangroves, where there are fewer predators, returning to the sea as they mature.

BONY FISHES

345

ORDER SILURIFORMES

Gafftopsail Sea Catfish Bagre marinus LENGTH

Up to 28 in (70 cm) WEIGHT

Up to 10 lb (4.5 kg) DEPTH

To 160 ft (50 m) DISTRIBUTION Gulf of Mexico, Caribbean Sea, and subtropical waters of western Atlantic

The most conspicuous feature of this silvery catfish is the pair of very long mouth barbels that extend back almost to the end of the pectoral fins. It has another pair of short barbels under the chin. The first rays of the large dorsal fin and the pectoral fins are drawn out as long, flat filaments and these fins also have a venomous serrated spine. When threatened, this catfish erects its dorsal fin and spreads out its pectoral fins like the sails of a yacht. sail-like dorsal fin

ORDER SILURIFORMES

Striped Catfish Plotosus lineatus LENGTH

Up to 13 in (32 cm) WEIGHT

Not recorded 3–200 ft (1–60 m)

DEPTH

DISTRIBUTION Red Sea and tropical waters in Indian and Pacific oceans

ORDER OSMERIFORMES

European Smelt Osmerus eperlanus LENGTH

18 in (45 cm) WEIGHT

Not recorded DEPTH

To 160 ft (50 m) DISTRIBUTION Temperate waters of northeastern Atlantic and Baltic Sea

The juveniles of this distinctive black-and-white striped catfish of the family Plotosidae stay together in dense, ball-shaped shoals and are often seen by divers over coral reefs. Adults live on their own or in small groups, but are well protected by a venomous, serrated spine in front of the first dorsal fin and each of the pectoral fins. A sting from an adult striped catfish can be dangerous to humans and is very occasionally fatal. These fish hunt at night, using four pairs of sensory Like salmon and trout, the European smelt has a dorsal fin and a small adipose fin on its back. The name of this fish derives from the fact that, when fresh, the European smelt has a strong smell that is reminiscent of cucumber. Adults swim in shoals in inshore waters, hunting small crustaceans and fish. They migrate up rivers to spawn, and the young fish are common in sheltered estuaries such as the Wash in southeast England (see p.128).

ORDER OSMERIFORMES

Capelin Mallotus villosus LENGTH

Up to 10 in (25 cm) WEIGHT

Up to 14/5 oz (52 g)

DISTRIBUTION

North Pacific, north Atlantic, and

Arctic Ocean

This small, silvery relative of salmon forms large shoals in cold and Arctic waters and is a vital food source for sea birds and marine mammals. The breeding success of some seabird

ORDER OSMERIFORMES

Barrel-eye Opisthoproctus soleatus LENGTH

Up to 4 in (10 cm) WEIGHT

Not recorded DEPTH 1,000–2,600 ft (300–800 m) DISTRIBUTION

Tropical and subtropical waters

worldwide

colonies has been linked to the abundance of capelin, and this in turn depends on environmental factors and exploitation by fishing. It is a major food source for Inuit peoples. Capelin are slim fish, with an olive-green back fading into silvery white on the sides. Shoals of this fish swim along with their mouths open, straining out plankton, which is caught on their modified gills. While this is their main source of food, they also eat worms and small fish. In spring, the schools move inshore, the males arriving first and waiting for the females. The males develop a band of modified scales along their sides and use these to massage the female, stimulating her to lay her eggs in the sand.

deeply forked tail

broad pectoral fin

Many fish that live in the twilight zone (see p.170), including the barrel-eye, have large eyes to make full use of what little light is available. As well as being large, the eyes of this species are tubular and point upward. This arrangement probably helps the barrel-eye to stalk other fish from below. Looking up, it is likely that it can pick out the silhouette of its prey or spot fish with bioluminescent patches on their undersides.

TIDAL BREEDING Capelin eggs make a good meal for many invertebrates and fish. To protect their eggs, large numbers of adult capelin swim into very shallow water at high tide and spawn on sandy beaches just below the tideline. Each female produces about 60,000 reddish, sticky eggs, which lie in the sand. When the eggs hatch after about 15 days, the larvae are washed out of the sand by the incoming tide and then swept out to sea on the outgoing tide.

OCEAN LIFE

DEPTH

0–1,000 ft (0–300 m)

barbels around the mouth to find worms, crustaceans, and mollusks hidden in the sand. During the day, they hide among rocks. Plotosids are the only catfish found in coral reefs. This species also ventures along open coasts and into estuaries. It spawns in the summer months. Male striped catfish build nests in shallow, rocky areas and guard the eggs for about ten days. The larvae are planktonic.

346

ANIMAL LIFE ORDER SALMONIFORMES

Atlantic Salmon Salmo salar Up to 5 ft

LENGTH

(1.5 m) WEIGHT

Up to 100 lb

(45 kg) DEPTH

Mostly surface

waters DISTRIBUTION Temperate and cold waters of north Atlantic and adjacent rivers

While most marine fish would quickly die in fresh water, the Atlantic salmon can move easily between river and sea. Fish with this ability are called anadromous. Designed for long-distance swimming, this fish has a powerful, streamlined body and a large tail. During their spawning runs, Atlantic salmon swim against strong river currents and leap up waterfalls to reach their spawning grounds. Before spawning, the salmon roam the north Atlantic for several years feeding on other fish. The Atlantic salmon is highly prized as a game fish, but wild salmon are becoming increasingly rare. HUMAN IMPACT

SALMON FARMING Floating fish farms rearing Atlantic salmon are common in Scottish sea lochs and Norwegian fiords. Salmon fry from freshwater hatcheries are later moved to submerged nets in saltwater farms. Environmental concerns focus on fish lice, which spread from the farms and infect wild fish, and on chemicals used to treat farmed fish.

ORDER SALMONIFORMES

Coho Salmon

Arctic Char

Oncorhynchus kisutch

Salvelinus alpinus

LENGTH

Up to 3 ft (1 m)

LENGTH

Up to 3 ft (1 m)

WEIGHT

Up to 33 lb

WEIGHT

Up to 33 lb

(15 kg)

(15 kg)

0–820 ft (0–250 m)

DEPTH

DEPTH

DISTRIBUTION Temperate and cold waters of north Pacific and adjacent rivers

OCEAN LIFE

ORDER SALMONIFORMES

Like most other salmon, the coho salmon is a fast, streamlined predator with excellent eyesight for spotting its prey. This makes it a challenging game fish for anglers. When ready to breed, mature fish find their way from the ocean back to the same river in which they were born. While swimming upstream, they develop bright red sides and a green head and back. When they reach the shallow waters at the river’s head, the females dig a nest, which is called a redd, in the gravel of the riverbed and lay their sticky eggs while the male fertilizes them. After spawning, the adults die and their bodies provide a feast for scavenging bears and other animals.

0–230 ft (0–70 m)

DISTRIBUTION Arctic Ocean and northern freshwater rivers and lakes

Arctic char are adapted for life in cold, oxygen-rich water and cannot tolerate warm or polluted water. There are two physiological races: a migratory form that lives in the sea but spawns in rivers, and a land-locked lake form. Migratory char grow to at least 3 ft (1 m) long and are regarded as excellent game fish. Shortly after the last ice age, they ranged much farther south but are now restricted to Arctic waters. The char that live in mountain lakes are relicts of this period.

ORDER STOMIIFORMES

Sloane’s Viperfish Chauliodus sloani LENGTH

Up to 14 in

(35 cm) WEIGHT

Up to 1 oz (30 g)

1,600–6,000 ft (475–1,800 m)

DEPTH

DISTRIBUTION

Tropical and temperate waters

worldwide

Deep-water fish are some of the most bizarre of all fish, and Sloane’s viperfish is no exception. At one end of its slender body it has a large head with huge, barbed teeth, while at the other it has a tiny forked tail. Rows of photophores run along the sides and belly and light the fish up like a night-flying airplane. During the day, it stays in deep water, but at night it migrates upward to feed where prey is more abundant. The single dorsal fin, just behind the head, has a very long first ray that can be arched over the head and may help entice prey within reach. Sloane’s viperfish spawns throughout the year. It is one of nine species of viperfish, all deep-living.

BONY FISHES ORDER STOMIIFORMES

Pacific Blackdragon Idiacanthus antrostomus LENGTH

Up to 15 in

(38 cm) WEIGHT

Up to 2 oz (55 g)

650–3,300 ft (200–1,000 m)

DEPTH

DISTRIBUTION Deep, tropical and temperate waters of eastern Pacific

thin tail

The Pacific blackdragon haunts the depths of the ocean, its black snake-like body lit up by photophores along its belly. When it opens its mouth, it reveals a set of long, dagger-sharp teeth. Hanging off the lower jaw is a barbel tipped by a glowing lure that can be moved to entice prey to venture within reach. The Pacific blackdragon is black on the inside as well as the outside, its black stomach preventing light from swallowed bioluminescent prey shining out. Male Pacific blackdragons are only about a quarter the size of the females. In the closely related species Idiacanthus fascicola, the young fish are similar in shape to the adults, but their eyes stick out on very long stalks. The stalks are absorbed as the fish grows and the eyes eventually come to lie in their sockets.

red-light photophore mouth filled with teeth

ORDER STOMIIFORMES

Stoplight Loosejaw Malacosteus niger

photophores

LENGTH

Up to 91/2 in

(24 cm) WEIGHT

Not recorded

3,300–13,000 ft (1,000–4,000 m) DEPTH

snakelike body

DISTRIBUTION

Deep tropical and temperate waters

worldwide barbel with lure

ORDER STOMIIFORMES

ORDER AULOPIFORMES

Lovely Hatchetfish

Tripodfish

Argyropelecus aculeatus

Bathypterois grallator

LENGTH

Up to 3 in

LENGTH

(8 cm) WEIGHT

Not recorded

WEIGHT

330–2,000 ft (100–600 m)

Tropical and temperate waters

worldwide

An expert at hiding from predators, the hatchetfish’s silvery coloration and use of bioluminescence conceals it against the downwelling light. They are also so thin that they are difficult to see head-on. This fish lives at medium depths and has large bulging eyes to make best use of what little light there is. At dusk, it rises up to 330–1,000 ft (100–300 m) to feed on small planktonic animals.

Not recorded

2,900–11,500 ft (875–3,500 m)

DEPTH

DISTRIBUTION

Up to 15 in

(37 cm)

DEPTH

DISTRIBUTION

Deep waters of Atlantic, Pacific, and

Indian oceans

Like many other deep-sea fish, the stoplight loosejaw is black, relatively small, and has a large mouth. However, it is unique in that it has no floor to its

DISTRIBUTION Deep waters of north Atlantic and Mediterranean

brown and red coloration camouflages the reef lizardfish, hiding it from larger predators. It can also bury itself in patches of sand, leaving only its head and eyes showing. Confident of its disguise, this fish will remain completely still and allow divers to approach to within a few inches before darting away to a new perch. It is caught and eaten by reef fishermen.

The spotted lanternfish is one of over 250 species of lanternfish found in the world’s oceans. Lanternfish are rather unprepossessing, small spindle-shaped fish with large eyes. However, in spite of their drab appearance they can put on an unrivaled display of light from an array of photophores along their sides and belly. In some species, males and females have different patterns of photophores, and this helps them to find each other in the dark depths. Photophore patterns also differ between species. Large shoals of spotted lanternfish are common in the north Atlantic. Along with other lanternfish, it is an important food source for larger fish, sea birds, and marine mammals. During the day it stays in deep water, at 800–2,500 ft (250–750 m), but at night it swims up to within about 330 ft (100 m) or even right to the surface, where it feeds on planktonic crustaceans and fish fry.

Reef Lizardfish Synodus variegatus LENGTH 8–16 in (20–40 cm)

Not recorded

16–295 ft (5–90 m) DEPTH

Tropical reefs in Red Sea, Indian Ocean, and western Pacific

DISTRIBUTION

ORDER MYCTOPHIFORMES

Spotted Lanternfish Myctophum punctatum LENGTH

Up to 41/4 in

(11 cm) WEIGHT

Not recorded

0–3,300 ft (0–1,000 m) DEPTH

OCEAN LIFE

The reef lizardfish habitually perches on the tops of rocks and corals, propped up on its long pelvic fins. From such vantage points, it keeps a lookout for passing shoals of fish, darting out and seizing one with its rows of sharp teeth. Its large mouth allows it to swallow quite big fish (as shown in the photograph). A variable blotchy

mouth, hence its name. Instead, a ribbon of muscle that joins the gill basket and the lower jaw contracts to shut the mouth. This arrangement may allow the fish a wider gape and a faster strike at prey. This fish is also a specialist in light production. It has two large photophores under each eye, one that produces normal blue-green bioluminescence and the other red. No natural red light reaches these depths, so most deep-sea creatures cannot see it. The red bioluminescence reflects well off a red animal, such as a shrimp, but the shrimp will be unaware that it has been spotlighted.

The deep ocean floor where the tripodfish lives consists largely of soft mud. So, to prevent itself from sinking into the ooze while lying in wait for its prey, this fish perches on a tripod made from elongated rays of its pelvic and caudal fins. Facing into the current, it waits for small crustaceans to drift within reach, catching them in its mouth, which has a large gape. The tripodfish has very small eyes and is thought to detect its prey by feeling for tiny vibrations in the water.

ORDER AULOPIFORMES

WEIGHT

347

348

ANIMAL LIFE ORDER LAMPRIFORMES

Opah

ORDER LAMPRIFORMES

Oarfish

Lampris guttatus

Regalecus glesne LENGTH

Up to 6 ft (2 m)

110–600 lb (50–275 kg) WEIGHT

DEPTH 330–1,300 ft (100–400 m)

LENGTH

Up to 36 ft (11 m) WEIGHT

Up to 600 lb (270 kg) 0–3,300 ft (0–1,000 m)

DEPTH

DISTRIBUTION Tropical, subtropical, and temperate waters worldwide

DISTRIBUTION Tropical, subtropical, and temperate waters worldwide

Roaming the oceans worldwide, the opah leads a nomadic existence. Shaped like a gigantic oval dinner plate, this colorful fish is a steely blue and green with silvery spots and red fins. Although it is toothless, the opah is an efficient hunter, catching squid and small fish. Rather than using its tail to swim, like most fish, it flies through the water by beating its long, narrow pectoral fins like a pair of wings. Opah regularly reach a weight of 110 lb (50 kg), although specimens as heavy as 600 lb (270 kg) have been reported. They spawn in the spring, laying eggs midwater, which hatch into larvae after 21 days. Also known as the moonfish, the opah is a valuable food fish in the Hawaiian Islands and on the west coast of mainland US. It is caught on long lines and with gill nets.

At up to 36 ft (11 m) in length, the oarfish is the longest bony fish known to science and is thought to be responsible for many sea serpent

ORDER GADIFORMES

Atlantic Cod Gadus morhua LENGTH

Up to 6 ft (2 m)

WEIGHT

Up to 200 lb

(90 kg) 0–2,000 ft (0–600 m) DEPTH

DISTRIBUTION

Temperate and cold waters of north

Atlantic

legends. Its bizarre appearance is enhanced by a crest of long red rays on its short, bluish head. These are followed by a bright red dorsal fin that runs the length of its silver body, which is marked with black streaks and spots. Its name comes from the pelvic fins, both of which extend as a single, long ray ending in an expanded tip, which looks like the blade of an oar. In the open ocean, the oarfish drifts in the currents, feeding on other fish and squid, its great length protecting it from most predators. Although it lives in tropical and temperate waters worldwide, the oarfish is rarely caught or seen alive, so little is known about its behavior.

ORDER GADIFORMES

Bib Trisopterus luscus LENGTH

Up to 18 in

(46 cm) WEIGHT

Up to 51/2 lb

(2.5 kg) 10–330 ft (3–100 m)

DEPTH

Temperate waters of northeastern Atlantic and western Mediterranean

DISTRIBUTION

Divers often see shoals of striped bib around rocky reefs and shipwrecks. These are usually younger fish or adults that have moved inshore to spawn. Large old fish often lose their banded pattern and become very dark. The bib has a much deeper body than most of its relatives in the family Gadidae. A long chin barbel and long pelvic fins help it to find crustaceans, mollusks, and worms to eat. The Atlantic cod is a powerful, heavily built fish with a large head, an overhanging upper jaw, and a single long chin barbel. It has small, elongated scales. The coloration varies from reddish, especially in young fish, to a mottled brown with a conspicuous white lateral line. The Atlantic cod is a shoal-forming fish, living in water over the continental shelf, and usually feeding at 100–250 ft (30–80 m) above areas of flat mud or sand. Adults migrate to established breeding grounds to spawn, usually in the early spring, with

each female releasing several squareended million eggs into tail the water. Atlantic cod can live for at least 25 years and mature fish can reach a weight of over 200 lb (90 kg), but sophisticated modern fishing techniques means that most cod are caught long before they reach this age and weight. Fish over 33 lb (15 kg) are now rare. However, Atlantic cod and its close relative Pacific cod are still among the world’s most important commercial species.

FINS AND SCALES

The Atlantic cod has three dorsal fins and two anal fins. Its small scales have growth rings, which can be counted to give its age. HUMAN IMPACT

OVERFISHING

OCEAN LIFE

Stocks of Atlantic cod were once thought to be inexhaustible, but numbers have declined drastically over most of its range. Cod exist as a number of discrete stocks that spawn in specific areas in water about 660 ft (200 m) deep. The collapse of stocks in Canada in the early 1990s led to fishing bans but after more than 20 years these are only now starting to recover. Management of North Sea stocks prevented collapse, and the stock is now slowly recovering.

FORAGING FOR FOOD

Atlantic cod feed both in midwater and on the seabed. They eat shoaling fish, such as herring, and also crustaceans, worms, and mollusks.

BONY FISHES ORDER GADIFORMES

ORDER GADIFORMES

Shore Rockling

Pacific Grenadier

Gaidropsarus mediterraneus

Coryphaenoides acrolepis

LENGTH

LENGTH

Up to 20 in (50 cm)

Up to 3 ft (1 m)

WEIGHT

WEIGHT

Up to 21/4 lb (1 kg)

Up to 61/2 lb (3 kg)

DEPTH

DEPTH

1,000–12,000 ft (300–3,700 m)

0–1,500 ft (0–450 m) DISTRIBUTION Temperate waters of northeastern Atlantic and Mediterranean

Rockling are eel-like in appearance, with two dorsal fins. The first of these is a fringe of short rays that ripple constantly. The shore rockling can be found in rock pools, where it uses its mouth barbels to find food. Most are dark brown, but some are paler.

DISTRIBUTION

ORDER GADIFORMES

Torsk Brosme brosme Up to 4 ft (1.2 m)

26–66 lb (12–30 kg) WEIGHT

DEPTH 65–3,300 ft (20–1,000 m) DISTRIBUTION

Temperate and cold waters of north

Atlantic

ORDER OPHIDIIFORMES

Pearlfish Carapus acus LENGTH

Up to 8 in (21 cm) WEIGHT

Not recorded DEPTH

To 330 ft (100 m) DISTRIBUTION Mediterranean; occasionally found in subtropical waters of eastern Atlantic

The adult pearlfish has a most unusual home—it lives inside the body cavity of sea cucumbers. To allow it to slip in and out of its host easily, it has an eel-like body, no pelvic fins, and no scales. It is a silvery-white color with reddish markings. At night, the pearlfish may swim out of the sea cucumber’s anus to go hunting for invertebrates to eat, returning to the body cavity tail first. However, the pearlfish may also eat the gonads and other organs of its host.

This heavily built member of the order Gadiformes lurks among rocks and pebbles in deep water offshore, where it searches for crustaceans and mollusks. It has thick lips, a long chin barbel, and a long dorsal and anal fin, each edged in white. In summer, two to three million eggs are laid, which float and develop near the surface. This species can live for 20 years. Torsk is fished commercially, especially off Norway, using trawls and lines, and it is also caught by anglers.

ORDER BATRACHOIDIFORMES

Oyster Toadfish Opsanus tau Up to 17 in

LENGTH

(43 cm) WEIGHT

Up to 41/4 lb

(2.2 kg) DEPTH

Not recorded

DISTRIBUTION Temperate and subtropical waters of northwestern Atlantic

Some people would consider the oyster toadfish an ugly animal, with its flat head, wide, toadlike mouth, and thick lips. It also has tassels around its chin, prominent eyes, and two dorsal fins, the first of which is spiny. Its shape and coloration provide camouflage in its home under rocks and debris. This hardy fish tolerates dirty and trash-strewn water and

ORDER OPHIDIIFORMES

Spotted Cusk-eel Chilara taylori Up to 15 in

(37 cm) WEIGHT

Not recorded

DISTRIBUTION

Temperate and subtropical waters of

eastern Pacific

As it is a favorite food of sea lions, cormorants, and other diving birds, the spotted cusk-eel is most active at night or on gloomy, sunless days. If

danger threatens, this eel-shaped fish can quickly slip between rocky rubble or bury itself tail-first in sand or mud. Unlike true eels, it has scales and pelvic fins. The latter are reduced to one split ray set very far forward under the head. Its eggs are laid in open water and hatch into larvae that live close to the surface. These develop into juveniles that drift for an extended period before settling down to a sea-bed existence. While the spotted cusk-eel lives in shallow water, one of its close relatives, the basketweave cusk-eel, has been found over 26,000 ft (8,000 m) deep in the abyssal zone (see p.182), the greatest depth for any fish.

The Pacific grenadier is one of about 300 different species of grenadiers that are found just off continental shelves and are abundant in every ocean. Grenadiers are also known as rattails because they have a large, bulbous head with big eyes, a sharp snout, and a long, scaly tail. The Pacific grenadier is dark brown with a tall dorsal fin. Another low fin runs along the back and all the way around the tail. This species spends most of its time near the seabed searching for food but it sometimes swims up into midwater, where it can catch squid, shrimp, and small fish.

COURTSHIP CALLS People living in houseboats along the east coast of the US are sometimes kept awake at night during April to October by loud grunting noises. The culprits are male oyster toadfish calling to attract females to lay their eggs in nests dug under rocks. The male makes these noises by vibrating the walls of his swim bladder using special muscles. The swim-bladder wall acts like the skin over a drum. The male guards the eggs until they hatch after about four weeks. is often found under jetties. It has been reared in captivity for use in experiments. It also does well in aquariums and is a popular game fish.

OCEAN LIFE

0–900 ft (0–280 m)

DEPTH

Deep, temperate waters of north

Pacific

LENGTH

LENGTH

349

350

sensory hairs

large mouth

ORDER LOPHIIFORMES

Hairy Angler Caulophryne jordani LENGTH Females up to 8 in (20 cm); males not recorded, but tiny WEIGHT

Not recorded

330–5,000 ft (100–1,500 m) DEPTH

DISTRIBUTION

Deep water worldwide

Anglerfish include some of the most bizarrely shaped fish in the ocean and the hairy angler certainly fits into this category. It has a huge mouth, tiny eyes, and large dorsal and anal fins

with very long projecting fin rays. It is also covered in sensory hairs, giving it a disheveled appearance. Like most anglerfish, it has a movable lure on top of the head that is formed from the first spine of the dorsal fin. The biology of the hairy angler is poorly known because only a few specimens have ever been captured. However, in other deep-sea anglerfish, this lure is used to attract prey within reach. The fish then opens its mouth and creates a sudden, strong inward suction current. The prey is engulfed within a fraction of a second. Food is scarce in the deep sea and anglerfish living here usually have extra-large mouths and expandable stomachs that

allow them to swallow prey as big or bigger than themselves. The hairy angler belongs to the family Caulophrynidae, also known as fanfins. The males of fish in this family are tiny and do not have lures. They live as parasites on the females when they are

ORDER LOPHIIFORMES

Deep-sea Angler Bufoceratias wedli Females up to 10 in (25 cm); males not recorded

LENGTH

WEIGHT

Not recorded

1,000–5,700 ft (300–1,750 m)

DEPTH

DISTRIBUTION

Gulf of Mexico, Caribbean Sea,

and Atlantic

ORDER LOPHIIFORMES

Polka-dot Batfish OCEAN LIFE

Ogcocephalus radiatus LENGTH

Up to 15 in (38 cm) WEIGHT

Not recorded DEPTH

0–230 ft (0–70 m) Subtropical waters of western Atlantic and Gulf of Mexico DISTRIBUTION

Fish of the family Ogcocephalidae, to which the polka-dot batfish belongs, are among the most oddly shaped of the anglerfish. They prop themselves up on paired pectoral and pelvic fins that enable them to walk over the sea bed in search of worms, crustaceans, and fish. Although the polka-dot batfish has a fishing lure, this is very short and evidence suggests it may secrete an odor that attracts potential prey. A hard, spiny skin protects these fish from predators, but they are so sluggish that divers can pick them up.

Living in the deep sea, this small, dark-colored anglerfish has a round body, delicate fins, and a luminescent lure at the end of a long rod called an illicium. A second, much smaller rod on the head is often hidden from view. It has a weak skeleton and small muscles that make it relatively light and

adult. This species is often difficult to identify because so few are caught and they are often damaged from contact with nets and from changes in pressure as they are brought to the surface. able to float more easily. It has no need to swim much as it lures its prey within reach. Female deep-sea anglers have been caught undamaged by research submarines using a piece of equipment called a slurp gun that sucks animals into a container. The fish have then been photographed alive. Males have not yet been seen but are likely to be tiny and free-living. rod and lure

round body

BONY FISH ORDER LOPHIIFORMES

ORDER LOPHIIFORMES

Coffinfish

Common Blackdevil

Chaunax endeavouri LENGTH

Melanocetus johnsonii Up to 9 in

(22 cm) WEIGHT

Not recorded

160–1,000 ft (50–300 m)

DEPTH

Temperate waters of southwestern Pacific, off east coast of Australia DISTRIBUTION

The coffinfish resembles a pink balloon covered in tiny spines and can make itself look bigger by inflating its body. It belongs to a family of

Females 7 in (18 cm); males (11⁄4 in) 3 cm LENGTH

anglerfish called Chaunacidae, or seatoads, that have large, flabby bodies and loose skin. Like other anglerfish, it has a lure but this is very small and can be hidden in a depression on the snout. Little is known of its life history, but it spends most of its time lying quietly on the bottom in muddy areas. It is usually found in deep water on the continental shelf and slope, but has also been found in water as shallow as 165 ft (50 m).

WEIGHT

Not recorded

To 6,600 ft (2,000 m) DEPTH

DISTRIBUTION

Deep waters of Atlantic, Pacific, and

Indian Oceans

This deep-sea anglerfish is also known as the humpback angler. The female common blackdevil has a huge head and large jaws with very long, daggerlike teeth, which are used to

ORDER LOPHIIFORMES

catch prey that may be larger than herself. Her stretchy stomach and loosely attached skin help her accommodate these huge meals. Although the female is not completely blind, her eyes are tiny and she probably cannot see her prey until she has enticed it within range using her glowing lure. By contrast, the male is tiny and uses his acute sense of smell to find a mate. He has no teeth but hangs on to the female with special hooks on his snout. When she has laid her eggs and he has fertilized them, he swims away, but how much longer he lives is not known. Both male and female juveniles live near the surface, where they feed on small planktonic animals.

glowing lure

Sargassumfish Histrio histrio LENGTH

Up to 8 in

(20 cm) WEIGHT

Not recorded

About 0–36 ft (0–11 m)

DEPTH

Tropical and subtropical seas worldwide; not recorded in eastern Pacific DISTRIBUTION

This unusual frogfish (family Anternnariidae) lives in floating rafts of sargassum seaweed. It uses its prehensile, leglike pectoral fins to clasp clumps of weed and scramble around

the rafts. With its skin tassels, mottled pattern, and variable color, the sargassumfish is well camouflaged and able to lure small fish and shrimps within striking range. If threatened, it can scramble onto the top of the seaweed raft. These fish are sometimes washed ashore with their rafts.

long, sharp teeth

ORDER LOPHIIFORMES

Regan’s Angler Haplophryne mollis Females 3 in (8 cm); males 3⁄4 in (2 cm)

LENGTH

WEIGHT

ORDER LOPHIIFORMES

Angler Lophius piscatorius LENGTH

Up to 6 ft (2 m) WEIGHT

Up to 125 lb

(57 kg) 65–3,300 ft (20–1,000 m)

DEPTH

DISTRIBUTION Northeastern Atlantic south to West Africa, Mediterranean, and Black Sea

The angler has a head like a flattened football fringed by a camouflage of seaweed-shaped flaps of skin, and a wide, flattened body that

tapers toward the tail. Its darkly marbled greenish-brown skin also helps the angler blend into the sediment of the sea floor. It lies patiently on the seabed, ready to suck in any fish that it can entice within range by flicks of the fleshy fishing lure on its dorsal fin. Large anglers have even been known to lunge up and catch diving birds. The species has well-developed pectoral fins, set on armlike bases, with sharp “elbows” that allow it to shuffle along over the sea floor. Anglerfish of the genus Lophius are also known as goosefishes or fishing frogs. This species is commercially exploited and sold as “monkfish.”

Not recorded

650–6,600 ft (200–2,000 m) DEPTH

DISTRIBUTION

Tropical and subtropical deep waters

worldwide

This unusual deep-sea anglerfish has unpigmented skin. The female of the species has an almost round body when mature, numerous very small teeth, spines above the eyes and behind the mouth, and a minimal fishing lure that consists of just a small flap on the snout. Like many other deep-sea anglerfish, the males of this species remain very small all their lives and their sole aim in life is to track down a female using their excellent sense of smell and latch onto her

using special hooks. Finding a mate in the depths of the ocean is difficult and by keeping the male attached, the female is assured that her eggs will be fertilized. The males eventually turn into parasites, biting into the female’s skin. In time their blood supplies fuse and the male then becomes nourished by the female. Up to three males have been found on a single female. unpigmented, translucent skin

351

352

ANIMAL LIFE ORDER GOBIESOCIFORMES

Cornish Sucker Lepadogaster purpurea LENGTH

3 in (7 cm) WEIGHT

Not recorded DEPTH

0–6 ft (0–2 m)

by turning over rocks and seaweeds and searching in rock pools. The color of the Cornish sucker is variable, but it always has two blue spots outlined in brown, red, or black behind its head, and it has a small tentacle in front of each eye. In the spring or summer, females lay clusters of golden yellow eggs on the undersides of rocks on the shore. The eggs are guarded by the parent fish until they hatch.

DISTRIBUTION Temperate waters of northeastern Atlantic, Mediterranean, and Black Sea

ORDER BELONIFORMES

Atlantic Flyingfish

Strong waves are no problem to this little fish—it can cling to rocks with a powerful sucker formed from its pelvic fins. It also has a low-profile body and a flattened, triangular head with a long snout that resembles a duck’s bill. This shape allows the fish to slip easily between the rocks and, because it is only a few centimetres long, it may be difficult to spot, but it can be found

ORDER BELONIFORMES

Hound Needlefish Tylosurus crocodiles LENGTH

Up to 5 ft (1.5 m) WEIGHT

Up to 14 lb (6.5 kg) DEPTH

0–43 ft (0–13 m) DISTRIBUTION

Tropical waters over coral reefs

worldwide

Cheilopogon heterurus LENGTH

Up to 16 in (40 cm) WEIGHT

Not recorded DEPTH

Surface waters DISTRIBUTION

Tropical and warm temperate waters

worldwide

Rendered almost invisible by its silvery color and needle-like shape, the hound needlefish swims along just beneath the surface, hunting for other fish that also live over coral reefs. Its long, thin snout is shaped like a spear, and it has been known to puncture small boats and cause severe injury to people by shooting up into the air when frightened. Although edible, the hound needlefish is not popular as a food fish because it has green-colored flesh.

ORDER BELONIFORMES

Atlantic Saury Scomberesox saurus LENGTH

Up to 20 in (50 cm) WEIGHT

Not recorded DEPTH

0–100 ft (0–30 m) North, northwestern, and eastern Atlantic and Mediterranean

DISTRIBUTION

ORDER BERYCIFORMES

Also known as the Mediterranean flyingfish, this species is distinguished by its very large, winglike pectoral and pelvic fins. If a predator, such as a tuna, attacks from below, the fish will beat its powerful forked tail rapidly, spread its “wings” at the last moment, and lift clear of the surface away from danger. The fish continues to beat its tail even in mid-flight and it can remain airborne for over 330 ft (100 m). The Atlantic flyingfish is edible, but is not commercially exploited. Although not as thin as its needlefish relatives, the Atlantic saury has a similar narrow body and a long, beak-like snout lined with tiny teeth. The body is clear green above and bright silver on the sides. It has a single dorsal and anal fin, each followed by a series of small finlets. This fish lives in large schools that chase and capture smaller fish and shrimplike crustaceans while skimming along at the surface. It is fished commercially and is caught by being attracted to bright lights at night.

ORDER BERYCIFORMES

Pineapplefish

Eyelight Fish

Cleidopus gloriamaris

Photoblepharon palpebratum

LENGTH

LENGTH

Up to 9 in (22 cm)

5 in (12 cm)

WEIGHT

WEIGHT

Up to 16 oz (500 g)

Not recorded

10–650 ft (3–200 m)

DEPTH

DEPTH

Temperate waters of eastern Indian Ocean and southwestern Pacific around Australia

DISTRIBUTION

ORDER BERYCIFORMES

Whitetip Soldierfish Myripristis vittata LENGTH

Up to 10 in (25 cm) WEIGHT

OCEAN LIFE

Not recorded DEPTH 10–260 ft ( 3–80 m) DISTRIBUTION

Tropical waters of Indian and Pacific

oceans

Soldierfish are nocturnal coral-reef residents that hide in groups in caves and beneath overhangs on steep reefs during the daytime. The whitetip

soldierfish is red, as are most members of its family (Holocentridae). The leading edges of its median fins are white. At depth, where natural red light does not penetrate, the fish’s red color appears black or gray, providing it with camouflage, especially on the deeper parts of the reef. Like many nocturnal fish, the whitetip soldierfish has large eyes, which help it to spot planktonic animals by dim moonlight and then snap them up. It has a short, blunt snout, large scales, and a deeply forked tail. Divers have observed that some individuals in a group of whitetip soldierfish often swim along upside down.

The pineapplefish is completely encased in armor consisting of large, thick, modified scales studded with spines. Each yellow scale is outlined in black, resembling a segment of pineapple skin. This fish, which lives in dark caves and under ledges on rocky reefs, has a pair of bioluminescent organs on its lower jaw that are hidden by the upper jaw when the mouth is closed. Orange during the day, the organs glow blue-green at night, when they are used to help find prey, such as crustaceans and small fish.

23–82 ft (7–25 m) DISTRIBUTION

Tropical waters of western and

central Pacific

The most characteristic feature of this small fish is the large light organ under each eye. The blue-green light can be turned on and off using a black membrane like an eyelid. These fish are active at night, often feeding in large groups, and use the light to signal to other individuals, startle predators, and find small planktonic animals to feed on. Eyelight fish are sometimes seen at night by divers on steep reef faces. Daytime sightings are rare, as these fish usually hide in caves during the day.

BONY FISHES ORDER BERYCIFORMES

Common Fangtooth Anoplogaster cornuta LENGTH

6–7 in (15–18 cm) WEIGHT

Not recorded 1,600–16,000 ft (500–5,000 m)

DEPTH

DISTRIBUTION Deep waters in temperate and tropical waters worldwide

The huge, saberlike teeth of this deep-water predator are designed to grab and hold onto other fish that may be as big as it is. The teeth are no good for cutting or chewing and so the common fangtooth swallows its prey whole, rather like a snake does. Adults are uniformly black or dark brown in color and can live as deep as 16,000 ft (5,000 m), but they are most common between 1,600 and 6,500 ft (500 and 2,000 m). They hunt by themselves or in small shoals,

searching for other fish to eat. Juvenile common fangtooths look very different from the adults and were classified as a separate species until 1955. They are light gray in color and have long spines on the head. They live in water as shallow as 160 ft (50 m) and feed mainly on crustaceans. Adult females shed their eggs directly into the sea, where they develop into planktonic larvae. The juveniles take on the adult shape when they are about 3 in (8 cm) long.

353

ORDER BERYCIFORMES

Orange Roughy Hoplostethus atlanticus 20–30 in (50–75 cm)

LENGTH

WEIGHT

Up to 15 lb (7 kg)

3,000–6,000 ft (900–1,800 m)

DEPTH

DISTRIBUTION North and south Atlantic, Indian Ocean, southwestern and eastern Pacific

This is one of the longest-lived fish species, with individuals having been recorded to reach at least 149 years old. It is a bright, brick-red color, but appears black in the dark waters in which it lives and this helps to hide it from predators. This deep-bodied, spiny fish that lives in deep water over rough ground and has a relatively limited home range. Deepsea fisheries now target this fish, and because it grows slowly and reproduces late, it cannot sustain heavy fishing. The Australian government listed it as threatened in 2006. soft rays

ORDER ZEIFORMES

John Dory Zeus faber LENGTH

Up to 3 ft (90 cm)

WEIGHT

Up to 18 lb

(8 kg) 15–1,300 ft (5–400 m)

DEPTH

DISTRIBUTION Eastern Atlantic, Mediterranean, Black Sea, Indian Ocean, western and southwestern Pacific.

The John Dory has one of the most distinctive appearances of all fish, with a rounded but very thin body, a heavy mouth, and tall fins. It is an expert hunter, stealthily approaching its prey head-on. In this attitude, its thin body is almost invisible and it can approach other fish closely. When it comes within striking range, it shoots out its protrusible jaws and engulfs its victim.

soft second dorsal fin

OCEAN LIFE

dark mark like a thumbprint

spiny first dorsal fin

DEEP-SEA FISHING

Trawling for fish in small boats is an arduous and often hazardous way of earning a living. Many fishermen have perished at sea over the years.

355

Fishing FISHING AND THE ENVIRONMENT

Exploitation of the sea’s bounty provides humans with

Traditional Fishing Traditional fishing using small-scale fishing gear is rarely a threat to fish stocks. Fish is an important food source, particularly in countries in the developing world, where it provides up to 80 percent of total protein needs. Fishing is also a vital part of the economy in these countries. And yet, such localized, traditional fisheries take only about 10 percent of the global total catch.

DAMAGE AND WASTE

BOTTOM TRAWLING Fishing gear dragged across the seabed damages marine life and stirs up sediment, smothering and damaging nearby animals. Heavy metal scallop dredges are particularly harmful.

HAZARDS TO WILDLIFE

high-quality food and many useful by-products, and sustains coastal fishing communities. Fish have long been seen as a resource that could never run out. However, modern industrial-scale fishing methods are taking their toll. Many stocks have collapsed, and some may be beyond recovery. The total global recorded catch of marine fish and shellfish rose steadily from 18.4 million tons in 1950 to 96.7 million tons in 1996, with a few dips associated with poor anchovy catches in El Niño years (see p.68-69). However, since that maximum, catches have declined and stabilized at about 88 million tons. The problems of ensuring a sustainable harvest from the sea are many. One fundamental difficulty is the “ownership” of stocks. There is little incentive for some to stop fishing in order to conserve fish if others continue, legally or illegally. It is difficult to police fisheries on the high seas, and illegal fishing is rife in some areas. It is notoriously problematic to accurately assess mobile fish stocks; and illegal fishing and trading and inaccurate reporting distort catch statistics. Many large-scale fishing methods are indiscriminate. There is vast waste, as unwanted and over-quota fish and invertebrate species are discarded, and many turtles, cetaceans, and sea birds are inadvertently caught. Nets with escape hatches for turtles and marked long lines to prevent albatrosses from being hooked are two of a number of new methods to reduce by-catch. Sand eels and other small fish, often termed “whitebait,” vital to sea birds such as puffins, are caught in industrial fisheries and turned into fishmeal for livestock.Yet not all fishing is unsustainable, and there is now increasing guidance for those consumers wishing to support well-managed fisheries and non-damaging fishing methods.

SHRIMP AND BYCATCH In every catch of shrimp, up to ten times their weight of other species is also caught in the net and subsequently discarded.

FISHING GEAR Thousands of animals die needlessly each year entangled in fishing tackle. This Hawaiian monk seal is one of a total population of under 1,000. TURTLE Drifting longlines for tuna, often dozens of miles long with thousands of hooks, also kill turtles, sharks, and marine birds. SCALLOP FARMING Farming scallops is an environmentally sound practice that avoids the adverse effects of trawling on the seabed and other species.

OCEAN LIFE

STILT FISHING This method of fishing is still practiced in parts of Sri Lanka and Thailand. The fishermen cast their lines while perching on poles in shallow water.

FISH FARMING

PEN-RAISED TUNA Fattening of wild tuna in cages falls between fishing and aquaculture legislation, and there are fears that this practice is further depleting overfished stocks.

356

ANIMAL LIFE ORDER SYNGNATHIFORMES

Leafy Seadragon Phycodurus eques LENGTH

14 in (35 cm) WEIGHT

It is hard to imagine anything less fishlike than the leafy seadragon. The bizarre tassels and frills that adorn its head and body form a spectacular camouflage that fools both predators and prey. Even its body and tail are bent and twisted to resemble seaweed stems. Closely related to

seahorses, the leafy seadragon has a similar, but much longer, tubular snout. This is an effective feeding tool—the fish aims its snout at a small shrimp and then sucks

Not recorded DEPTH

13–100 ft (4–30 m)

hard, rather like a person would on a drinking straw. The leafy seadragon lives on rocky, seaweed-covered reefs and in seagrass beds. Unlike seahorses, it cannot coil its tail around an object. It moves very slowly and sways with the waves, mimicking the seaweed. Like seahorses and pipefish, the female deposits her eggs in a brood pouch under the male’s tail and he carries them until they hatch.

Eastern Indian Ocean, along the southern coast of Australia DISTRIBUTION

ORDER SYNGNATHIFORMES

Trumpetfish Aulostomus maculatus LENGTH

Up to 3 ft (1 m)

hunts by lying in wait to ambush passing shoals of fish, but it is also known to follow predatory fish such as moray eels and steal some of the fish that they flush from their hiding places.

ORDER SYNGNATHIFORMES

Harlequin Ghost Pipefish Solenostomus paradoxus LENGTH

WEIGHT

5 in (12 cm)

Not recorded

WEIGHT

DEPTH

Not recorded

7–80 ft (2–25 m)

DEPTH

DISTRIBUTION Gulf of Mexico, Caribbean Sea, and subtropical waters of western Atlantic

Not recorded Tropical reefs in Indian Ocean and western and southwestern Pacific

DISTRIBUTION

The trumpetfish looks like a piece of drifting wood, hiding itself among sea fans and other corals. It has a long, slender, straight body, and when it flares open its mouth, its long snout resembles a thin trumpet. The trumpetfish is usually brown, but some individuals have a yellow body. It

ORDER SYNGNATHIFORMES

Short-snouted Seahorse Hippocampus hippocampus

ORDER SYNGNATHIFORMES

Snake Pipefish Entelurus aequoreus LENGTH

Up to 24 in (60 cm) WEIGHT

OCEAN LIFE

Not recorded DEPTH

33–330 ft (10–100 m) DISTRIBUTION

Temperate waters of northeastern

Atlantic

At first sight, the snake pipefish could easily be mistaken for a small sea snake. It has a long, smooth, rounded body tapering to a thin tail with

a minute tail fin. However, like all pipefish and seahorses, its head is drawn out into a distinctive tubular snout for sucking up small floating crustaceans and fish fry. Pipefish have no scales but, instead, the body is encased in segmented bony armor lying beneath the skin. The snake pipefish has an orangebrown body with pale blue bands. It lives among seaweed, where it is well camouflaged. The female lays several hundred eggs into a shallow pouch along the male’s belly during the summer.The eggs develop in the pouch and the young are released when they are about 1/2 in (1 cm) long, but before they are fully developed.

LENGTH

6 in (15 cm) WEIGHT

Not recorded DEPTH

16–200 ft (5–60 m) Temperate and subtropical waters of northeastern Atlantic and Mediterranean

DISTRIBUTION

In the seahorse world, it is the males that give birth to the young. After an elaborate courtship dance, the female lays her eggs in a special pouch on the male’s belly. The pouch seals over until the eggs hatch and the tiny baby seahorses emerge. This species is distinguished by its short snout, which is less than a third of the head length.

The harlequin ghost pipefish looks as though it has wings attached to the sides of its long, thin body. In reality, these are greatly enlarged pelvic fins in which the female broods her eggs. The fins are modified to form a pouch, where the eggs remain until they hatch. This uncommon species occurs in a wide variety of bright colors and patterns that mimic the reef feather stars and black corals among which it lives. It also often swims head-down and so gains further camouflage by aligning its body with the branches among which it swims.

BONY FISHES ORDER SYNGNATHIFORMES

Pygmy Seahorse Hippocampus bargibanti LENGTH

1 in (2.5 cm) WEIGHT

Not recorded DEPTH

50–165 ft (15–50 m) DISTRIBUTION

Tropical waters of southwestern

Pacific

This miniature seahorse lives on Muricella sea fans and was originally discovered when a sea fan was collected for an aquarium. It is very difficult to spot as its body is covered in tubercles that exactly match the polyps of its host. Clinging on tightly with its prehensile tail, it reaches out into the water to suck in planktonic animals. Like other seahorses, it has a rigid body made up of bony plates and a head that is tucked in like a tightly reined carriage horse.

ORDER SYNGNATHIFORMES

ORDER SCORPAENIFORMES

Razorfish

Stonefish

Aeoliscus strigatus

Synanceia verrucosa

LENGTH

LENGTH

6 in (15 cm)

Up to 16 in (40 cm)

WEIGHT

WEIGHT

Not recorded

Up to 51/2 lb (2.5 kg)

DEPTH

DEPTH

3–65 ft (1–20 m)

3–100 ft (1–30 m)

DISTRIBUTION Tropical reefs in Indian Ocean and western Pacific

DISTRIBUTION Tropical waters of Indian Ocean and western Pacific

357

ORDER GASTEROSTEIFORMES

Three-spined Stickleback Gasterosteus aculeatus LENGTH

4 in (11 cm) WEIGHT

Not recorded DEPTH

0–330 ft (0–100 m) DISTRIBUTION Temperate waters of north Atlantic and north Pacific

The three-spined stickleback is equally at home in fresh water and sea water. It has three sharp spines on its back and a series of bony plates along its sides. This species is best known for its breeding behavior, which involves the male building a tunnel-like nest of plant material into which he entices one or more females to lay their eggs. He fans oxygenated water over the eggs as they develop. The stonefish is the world’s most venomous fish, and its sting is capable of killing a human. Each sharply tipped spine of the dorsal fin has a venom gland at the base from which a duct runs in a groove to the spine tip. Lying quietly on rocks or sediment in the shallows, the stonefish matches its color to its background and is easily stepped on. Its camouflage helps it to ambush passing fish, which are sucked into its cavernous mouth with lightening speed.

While some reef fish habitually swim upside down, razorfish swim in synchronized groups in a vertical position, with their long, tubular snouts pointing down. These strange fish are encased in transparent bony plates that meet in a sharp ridge along the belly, like the edge of a razor, and also form a sharp point at the tail. A dark stripe along the body provides camouflage for the razorfish when hiding among sea urchins and branched corals.

ORDER SCORPAENIFORMES

Lionfish Pterois volitans LENGTH

Up to 15 in (38 cm) WEIGHT

Not recorded DEPTH

7–180 ft (2–55 m) Tropical waters of eastern Indian Ocean and western Pacific

DISTRIBUTION

Long-spined Bullhead Taurulus bubalis LENGTH

Up to 10 in (25 cm) WEIGHT

Not recorded DEPTH

0–330 ft (0–100 m) DISTRIBUTION Temperate waters of northeastern Atlantic and western Mediterranean

Bullheads are small, cold-water relatives of scorpionfish and the stonefish (see above). Like them, they are stout, bottom-living fish with a broad head, large mouth, and spiny fins. The long-spined bullhead also has a long, sharp spine on each cheek. None of its spines is venomous. These small fish can be found in rock pools, but are difficult to spot as they match their color to their background. In the winter, the female lays clumps of eggs between rocks. These are then guarded by the male until they hatch between five and 12 weeks later.

OCEAN LIFE

Although the lionfish can inflict a painful sting, it is usually not dangerous to humans. Its flamboyant coloration of red stripes serves as a warning both to divers and to would-be predators. Also known as the turkeyfish, it hunts at night using its winglike pectoral fins to trap its prey of fish, shrimp, and crabs against the reef.

ORDER SCORPAENIFORMES

358

ANIMAL LIFE ORDER SCORPAENIFORMES

Spotted Scorpionfish Scorpaena plumieri LENGTH

Up to 18 in (45 cm)

ORDER SCORPAENIFORMES

East Atlantic Red Gurnard

ORDER SCORPAENIFORMES

Lumpsucker Cyclopterus lumpus

Chelidonichthys cuculus

LENGTH

Up to 24 in (60 cm)

LENGTH

WEIGHT

WEIGHT

Up to 20 in (50 cm)

Up to 31/4 lb (1.5 kg)

Up to 21 lb (9.5 kg)

WEIGHT

DEPTH

DEPTH

Not recorded

3–200 ft (1–60 m)

DEPTH

DISTRIBUTION Western Atlantic and eastern Atlantic around Ascension Island and St. Helena

50–1,300 ft (15–400 m)

7–1,300 ft (2–400 m) DISTRIBUTION

Temperate and cold waters of north

Atlantic

The adult lumpsucker (or lumpfish) has a slightly grotesque appearance because the first dorsal fin becomes overgrown with thick, lumpy skin. Other bony lumps and bumps stick out in irregular rows along its large, rounded body. The pelvic fins form a strong sucker disk on its belly, which the lumpsucker uses to cling to wave-battered rocks near the shore where it spawns. The male guards the eggs from crabs and also fans them. Lumpsucker eggs are marketed as substitute caviar.

Temperate waters of northeastern Atlantic and Mediterranean DISTRIBUTION

Resting quietly on the seabed, the spotted scorpionfish is almost invisible thanks to its mottled color and weedlike skin flaps that cover its head. However, if this fish is disturbed, it can open its large pectoral fins to display dramatic black and whitespotted patches. Flashing these “false eyes” is often enough to frighten off a potential predator, but if this does not work, the spines on its dorsal fin can inflict a venomous sting.

ORDER PERCIFORMES

Potato Grouper Epinephelus tukula LENGTH

Up to 7 ft (2 m) WEIGHT

Up to 240 lb (110 kg) DISTRIBUTION

33–500 ft (10–150 m)

OCEAN LIFE

DISTRIBUTION Tropical waters of Red Sea, Gulf of Aden, and western Pacific

Groupers are large and important predators on coral reefs. They help to maintain the health of a reef by picking off weak fish. They also eat crabs and spiny lobsters. The potato grouper inhabits deeper reef channels and seamounts. It has a large head and heavy body with a single long, spiny dorsal fin. Irregular dark blotches cover the body and dark streaks radiate from the eyes. These fish are territorial, and in some areas, individuals are hand-fed by divers. However, one diver drowned after being rammed in the chest by a large potato grouper. The large size of these fish makes them an easy target for spearfishermen.

Wreckfish

Fairy Basslet

Polyprion americanus

Pseudanthias squamipinnis

LENGTH

LENGTH

Up to 7 ft (2 m)

Up to 6 in (15 cm)

WEIGHT

WEIGHT

Up to 220 lb (100 kg)

Not recorded

DEPTH

DEPTH

130–2,000 ft (40–600 m)

The East Atlantic red gurnard could be said to be a “walking-talking” fish. The first three rays of the pectoral fins are shaped as separate, thick, fingerlike feelers, which are covered with sensory organs.These feelers are used to “walk” over the seabed and probe for shrimp and crabs. The fish has a large head protected by hard, bony plates and spines and two separate dorsal fins. These gurnards sometimes form shoals, and as the fish move around, they make short, sharp grunting noises by vibrating their swim bladder with special muscles and so stay in contact with other gurnards nearby.They spawn in spring and summer and the eggs and larvae float freely near the surface. Adults live for at least 20 years. Although caught commercially, this species is not a main target for fishing.

ORDER PERCIFORMES

ORDER PERCIFORMES

0–180 m (0–55 m)

DISTRIBUTION

Atlantic, Mediterranean, Indian Ocean, and Pacific

DISTRIBUTION

The name of this fish comes from the juveniles’ habit of accompanying drifting wreckage. This is a large, solid fish with a pointed head and a protruding lower jaw. It has a spiny dorsal fin and a bony ridge running across the gill cover. Adult wreckfish live close to the bottom of the sea floor and often lurk inside shipwrecks and caves. Juvenile wreckfish prefer surface waters and can often be approached by snorkelers, presumably because the fish consider the swimmers to be floating wreckage. As the young fish grow, they give up their nomadic life to live near the seabed. Adults are fished using lines and make good eating.

Fairy basslets live around coral outcrops and dropoffs. The larger, more colorful males have a long filament at the front of the dorsal fin, and they defend a harem of females. As they grow larger, the females change sex and turn into males.

Red Sea and tropical waters of Indian Ocean and western Pacific

BONY FISHES ORDER PERCIFORMES

Harlequin Sweetlips

359

JUVENILE COSTUME

Plectorhinchus chaetodonoides LENGTH

Up to 28 in (72 cm) WEIGHT

Up to 15 lb (7 kg) DEPTH

3–100 ft (1–30 m) Tropical waters of Indian Ocean and western Pacific

DISTRIBUTION

ORDER PERCIFORMES

Common Bluestripe Snapper Lutjanus kasmira LENGTH

Up to 16 in (40 cm) WEIGHT

Not recorded DEPTH

10–870 ft (3–265 m) Tropical reefs of Red Sea, Indian Ocean, and Pacific DISTRIBUTION

ORDER PERCIFORMES

Red Bandfish Cepola macrophthalma LENGTH

Up to 30 in (80 cm) WEIGHT

Not recorded DEPTH

50–1,300 ft (15–400 m) Temperate and subtropical waters of northeastern Atlantic and Mediterranean DISTRIBUTION

Very little was known about this strange fish until the 1970s, when divers discovered a population in shallow water around Lundy Island

Divers often see large shoals of common bluestripe snapper around coral and rock outcrops during the day. Their streamlined bodies mean that they can swim fast when they disperse at night to feed on smaller fish and bottom-dwelling crustaceans. They have a single long dorsal fin, which, like all their fins, is bright yellow. The common bluestripe snapper and many other similar species are important commercial fish. Their beautiful colors also make them popular specimens among aquarium-fish enthusiasts. off the west coast of Britain. The red bandfish is shaped like an eel but flattened from side to side, with a long, golden-yellow fin running the length of the body on both sides. In mature males, the fin has a bright blue edge. These fish live in deep mud burrows, emerging just far enough to feed on passing arrow worms and other plankton in the manner of tropical garden eels (see p.343). They also swim free of their burrows at times. In addition to single burrows, colonies of many thousands of individuals have been discovered. The burrows sometimes connect with those of burrowing crabs, and this may be a deliberate association.

Small groups of harlequin sweetlips can often be seen gathered at dusk around large coral heads, waiting to be cleared of parasites by a cleaner wrasse (see p.361). These deep-bodied fish are patterned with small, brownish black spots that break up their outline as they swim among the everchanging shadows on the reef. Their name comes from their thickened lips, which they use to dig out invertebrates from sand.

ORDER PERCIFORMES

Bluecheek Butterflyfish Chaetodon semilarvatus LENGTH

Up to 9 in (23 cm) WEIGHT

Not recorded DEPTH

10–65 ft (3–20 m) DISTRIBUTION

Coral reefs in Red Sea and Gulf

of Aden

Ring-tailed Cardinalfish Apogon aureus LENGTH

Up to 6 in (15 cm) Not recorded 3–130 ft (1–40 m) Red Sea and tropical waters of Indian Ocean and western Pacific DISTRIBUTION

Cardinalfish are small nocturnal reef fish. The ring-tailed cardinalfish hides under corals and in crevices during the day and emerges at night

Queen Angelfish Holacanthus ciliaris

to feed on plankton. It has a distinctive black band around the tail base and two blue and white lines running from the snout through the eyes. Like all of the 350 or so species of cardinalfish, it has two separate dorsal fins. The male does not feed during the breeding season. Instead, after the female has laid her eggs the male broods them in his mouth, protecting them until they hatch.

Butterflyfish provide testimony to the health of a coral reef. A wide variety and plentiful numbers of these brightly colored, disk-shaped fish indicate that a reef is flourishing. Bluecheek butterflyfish are usually seen in pairs and often hide under table corals. The blue eye-patch hides the eye and confuses predators.

Up to 18 in (45 cm) WEIGHT

Up to 31/4 lb (1.5 kg) DEPTH

3–230 ft (1–70 m) DISTRIBUTION Gulf of Mexico, Caribbean Sea, and subtropical waters of western Atlantic

One of the most colorful Caribbean reef fish, the blue and yellow queen angelfish slips its slim body effortlessly between corals and sea fans. It uses its small mouth and brushlike teeth to nibble sponges, which are its main food. Like all angelfish, it has a sharp spine at the corner of the gill cover. Juveniles are brown and yellow with curved blue bars and feed on parasites that they pick from other fish.

OCEAN LIFE

DEPTH

ORDER PERCIFORMES

LENGTH

ORDER PERCIFORMES

WEIGHT

Juvenile harlequin sweetlips have a different patterning than the adults. They have brown bodies and white spots edged in black. By swimming in a weaving, undulating fashion, the smallest juveniles mimic a toxic flatworm with a similar coloration and so escape predation. Their color may also warn that they themselves are unpalatable to predators.

360

ANIMAL LIFE ORDER PERCIFORMES

Bigeye Trevally Caranx sexfasciatus LENGTH

Up to 4ft (1.2m) WEIGHT

Up to 40lb (18kg) DEPTH

3–330ft (1–100m) DISTRIBUTION

Tropical waters of Indian Ocean

and Pacific

During the day, shoals of bigeye trevally spiral lazily in coral reef channels and next to steep reef slopes, but at night, these fast-swimming

predators split up and scour the reef for prey. Built for speed, these silvery fish have a narrow tail base, which is reinforced with bony plates called scutes, and a forked caudal fin. The first dorsal fin folds down into a groove to improve the streamlining of the fish, and the pectoral fins are narrow and curved. There are many different species of trevally, which are difficult to tell apart. The bigeye trevally has a relatively large eye and the second dorsal fin usually has a white tip. These fish make good eating and are common in local markets in Southeast Asia. Juvenile bigeye trevally live close inshore and may enter estuaries and rivers.

ORDER PERCIFORMES

Pilotfish Naucrates ductor LENGTH

Up to 28in (70cm) WEIGHT

Not recorded DEPTH

0–100ft (0–30m) Tropical, subtropical, and temperate waters worldwide

DISTRIBUTION

ORDER PERCIFORMES

Sharksucker Echeneis naucrates LENGTH

Up to 3 ft (1m) WEIGHT

Up to 5lb (2.3kg) DEPTH

65–165ft (20–50m) Tropical, subtropical, and temperate waters worldwide

DISTRIBUTION

Although a member of the predatory trevally family Carangidae (see left), the pilotfish has taken up a scavenging, nomadic existence, traveling with large, ocean-dwelling bony fish, sharks, rays, and turtles. Its slim, silvery to pale bluish body is marked with six or seven bold black bands. These may help the host fish recognize it and so leave it alone. Darting in when its host has made a kill, the pilotfish eats any scraps it can find and also removes parasites.Young fish associate with jellyfish. The distinctive feature of the sharksucker is the powerful sucker disk on the top of its head, which enables it to attach itself securely to another fish. It feeds on its host’s scraps and parasites, and also on small fish. Usually found attached to sharks or other large fish, cetaceans, and turtles, the sharksucker also swims freely over coral reefs. Its body is long and thin and ends in a fanlike tail.

ridged oval sucker disk replaces first dorsal fin

lower jaw juts out beyond upper jaw

ORDER PERCIFORMES

ORDER PERCIFORMES

Dolphinfish

Sergeant Major

Coryphaena hippurus

Abudefduf saxatilis

LENGTH

LENGTH

Up to 7ft (2.1m)

Up to 9in (23cm)

WEIGHT

WEIGHT

Up to 88lb (40kg)

Up to 7oz (200g)

DEPTH

DEPTH

0–280ft (0–85m)

3–50ft (1–15m)

Tropical, subtropical, and temperate waters worldwide

DISTRIBUTION

With its shimmering colors, a dolphinfish leaping clear of the water is a spectacular sight. Metallic blues and greens cover its back and sides, grading into white and yellow on the underside. A fast ocean-dwelling fish, it is powered by a long, forked tail, with a single elongated dorsal fin providing stability. Also known as the dorado, it is a valuable market fish.

This small fish is a familiar sight on most coral reefs in the Atlantic. It is one of the most common members of the damselfish family (Pomacentridae). It feeds on zooplankton in large groups, gathering above the reef to pick tiny animals and fish eggs from the water. In tourist areas, the fish are attracted to divers and boats, and will eat almost anything that is offered. Male sergeant majors prepare a nesting area and guard the eggs laid by the females. A similar species, Abudefduf vaigiensis, is found on reefs in the Indo-Pacific region.

DISTRIBUTION

Atlantic Ocean

ORDER PERCIFORMES

False Clown Anemonefish Amphiprion ocellaris LENGTH

Up to 4in (11cm) WEIGHT

Not recorded

OCEAN LIFE

Tropical and subtropical waters of

DEPTH

3–50ft (1–15m) DISTRIBUTION Tropical waters of eastern Indian Ocean and western Pacific

The most surprising thing about the false clown anemonefish is its home. It lives inside a giant stinging anemone. This small orange and white fish

spends its whole life with its chosen anemone, which can be one of three species. At night, it sleeps among the bases of the tentacles on the anemone’s disk. The fish is not stung and eaten because the anemone does not know it is there: a special slime covers the fish’s body and prevents the anemone from recognizing it as food. Each anemone usually supports a large female, her smaller male partner, and several immature fish. If the female dies, the male changes sex and becomes female and the largest immature fish takes on the male role. Both the false clown and the clown anemonefish are among the most popular aquarium fish, and numbers have been reduced in some areas by overcollecting.

BONY FISH ORDER PERCIFORMES

ORDER PERCIFORMES

Cuckoo Wrasse

Cleaner Wrasse

Labrus mixtus

Labroides dimidiatus LENGTH

LENGTH

Up to 16in (40cm)

51/2 in (14cm)

WEIGHT

WEIGHT

Not recorded

Not recorded

DEPTH

7–650ft (2–200m) DISTRIBUTION Temperate and subtropical waters of northeastern Atlantic and Mediterranean

The cuckoo wrasse is one of the most colorful fish in northern European waters. Large mature males (shown here) are a beautiful blue and orange, while females are pink with alternate black and white patches along the back. When they are 7–13 years old, some females change color and

DEPTH

sex and become fully functional males. These males are known as secondary males and spawn in pairs with females. The male excavates a nest and attracts the female with an elaborate swimming display. To further complicate matters it has been found that a very few fish are born male but have the female coloring. These males are known as primary males and their role in reproduction has not been fully ascertained.

3–130ft (1–40m) DISTRIBUTION Tropical reefs in Indian Ocean and southwestern Pacific

361

MUTUAL BENEFIT Skin parasites are irritating and fish can be debilitated by a heavy infestation. On coral reefs, large fish line up at known “cleaning stations” such as a prominent coral head, spread their fins, and open their mouths. The resident cleaner wrasse picks off parasites and dead tissue and gets a good meal in return.

The cleaner wrasse spends its life grooming other fish, turtles, and occasionally even divers. This little fish is silvery blue with a black band running from snout to tail. The “client” recognizes it from its markings and does not try to eat it. Groups of cleaner wrasse usually consist of an adult male and a harem of females. If the male dies, the largest female changes sex and takes on the male role, becoming fully functional within a few days. distinctive black band

small mouth with strong teeth

ORDER PERCIFORMES

Green Humphead Parrotfish Bolbometopon muricatum LENGTH

Up to 41/4 ft (1.3m) WEIGHT

Up to 100lb (46kg) DEPTH

3–100ft (1–30m) DISTRIBUTION Tropical reefs in Red Sea, Indian Ocean, and southwestern Pacific

ORDER PERCIFORMES

Blackfin Icefish Chaenocephalus aceratus LENGTH

Up to 28in (72cm) WEIGHT

Up to 7½lb (3.5kg) ORDER PERCIFORMES

Wolf-fish Anarhichas lupus LENGTH

Up to 5ft (1.5m) WEIGHT

Up to 53lb (24kg) 3–1,650ft (1–500m) DISTRIBUTION

North Atlantic and Arctic Ocean

This large and ferocious-looking fish is normally found on rocky reefs in deep water. However, north of the British Isles, divers regularly see them in shallow water. They are not aggressive to divers unless provoked.

DEPTH

16–2,500ft (5–770m) DISTRIBUTION Polar waters of Southern Ocean around northern Antarctica

In the freezing waters around Antarctica, the temperature can fall to nearly 28˚F (-2˚C). This is below the temperature at which the blood of most fish would freeze. The blackfin icefish has a natural antifreeze in its blood that helps it survive in these conditions. It has no red blood cells and so appears a ghostly white. This makes its blood thinner so that it can flow freely in the cold temperatures. It is a sluggish hunter of small fish and krill and needs little oxygen.

OCEAN LIFE

DEPTH

The wolf-fish has a long body and a huge head with strong caninelike teeth at the front and molarlike teeth at the sides. These are used to break open hard-shelled invertebrates such as mussels, crabs, and sea urchins. Worn teeth are replaced each year. The skin is tough, leathery, and wrinkled and is usually greyish with darker vertical bands extending down the sides. Spawning takes place during the winter. The female lays thousands of yellowish eggs in round clumps among rocks and seaweeds and the male guards them until they hatch. In spite of their unattractive appearance, wolf-fish are good to eat and are caught by anglers. They are also sometimes caught in trawl nets.

Parrotfish are aptly named—not only are they brightly colored, but also their teeth are fused together to form a parrotlike beak. The green humphead parrotfish is much larger than most of its relatives. It has a huge crest-shaped hump on its head, a greenish body, large scales, and a single long dorsal fin. This destructive fish feeds by crunching up live coral, and it often breaks up the coral with its head. However, on the positive side, the coral sand it defecates after a meal helps to consolidate the reef and build up patches of sand.

BIGEYE TREVALLIES

These bigeye trevallies, also known as bigeye jacks, are shoaling in shallow water near the Solomon Islands in the western Pacific. They are usually slow-moving by day, but at night the shoals disperse and they hunt singly, moving quickly in search of the fish and crustaceans on which they feed.

364

ANIMAL LIFE ORDER PERCIFORMES

Common Stargazer Kathetostoma laeve LENGTH

Up to 30 in

(75 cm) WEIGHT

Not recorded

200 ft (0–60 m), possibly 550 ft (150 m) DEPTH

Temperate waters of Indian Ocean around southern Australia DISTRIBUTION

Looking like a cross between a bulldog and a seal, the common stargazer normally lies buried in shelly sand. It has its eyes set right on top of its

large, square head and its mouth slants obliquely upward. This allows it to breathe and to see while remaining almost completely buried and is probably the reason behind its unusual name. Its large, white-edged pectoral fins help it to lunge out of the sand and engulf passing fish and crustaceans. Common stargazers have also occasionally bitten divers who have inadvertently disturbed them while on night dives, when they are particularly difficult to spot. Anglers face a greater threat if they catch a common stargazer. Careless handling can result in a painful sting from a tough, venomous spine that lies behind each gill cover.

ORDER PERCIFORMES

broad caudal fin

Tompot Blenny

ORDER PERCIFORMES

ORDER PERCIFORMES

Greater Weever

Sand Eel

Trachinus draco

Ammodytes tobianus LENGTH

LENGTH

Up to 20 in (50 cm)

Up to 8 in (20 cm)

WEIGHT

WEIGHT

Up to 41/2 lb (2 kg)

Not recorded

DEPTH

DEPTH

3–500 ft (1–150 m)

0–100 ft (0–30 m)

DISTRIBUTION

Temperate waters of northeastern Atlantic and Mediterranean

DISTRIBUTION

The greater weever is one of very few venomous fish found in European waters. It has a long body, large eyes, and two dorsal fins, the first of which has venomous spines. During the day, the fish lies buried in the sand with just its eyes and fin-tip exposed. A painful wound can result from stepping on the fish in shallow water.

Shimmering shoals of sand eels are a familiar sight in shallow sandy bays around northern Europe. These small, silvery fish have long, thin bodies with a pointed jaw and a single long dorsal fin. Large shoals patrol the waters just above the seabed, feeding on planktonic crustaceans, tiny fish, and worms. If threatened, they dive down and disappear into the sand. In winter, they spend most of the time buried. Sand eels form a very important part of the diet of larger fish such as cod, herring, and mackerel, and of sea birds, especially Atlantic puffins. When sand eels are scarce, local puffin colonies produce very few young. In some areas, overexploitation of sand eels for processing into fishmeal has been linked to seabird declines (see p.403).

large eye

Temperate waters of northeastern Atlantic and Baltic Sea

ORDER PERCIFORMES

Bignose Unicornfish

Parablennius gattorugine

Naso vlamingii

LENGTH

LENGTH

Up to 12 in (30 cm)

Up to 24 in (60 cm)

WEIGHT

WEIGHT

Not recorded

Not recorded

DEPTH

DEPTH

3–100 ft (1–30 m)

3–165 ft (1–50 m)

Temperate and subtropical waters of northeastern Atlantic and Mediterranean DISTRIBUTION

With its thick lips, bulging eyes, and a pair of tufted head tentacles, the tompot blenny is a comical-looking fish. Like all blennies, it has a long body, a single long dorsal fin, and peg-like pelvic fins, which it uses to prop itself up. Inquisitive by nature, the tompot blenny will peer out at approaching divers from the safety of a rock crevice.

large pelvic fins

ORDER PERCIFORMES

Mandarinfish Synchiropus splendidus LENGTH

Up to 21/2 in (6 cm) WEIGHT

Not recorded DEPTH

3–60 ft (1–18 m) DISTRIBUTION

Tropical waters of southwestern

Pacific

ORDER PERCIFORMES

Yellow Shrimp Goby OCEAN LIFE

Cryptocentrus cinctus LENGTH

Up to 3 in (8 cm) WEIGHT

Not recorded DEPTH

3–50 ft (1–15 m) Tropical waters of northeastern Indian Ocean and southwestern Pacific DISTRIBUTION

With its yellow and orange body and distinctive green and blue markings, the mandarinfish is one of the most colorful of all reef fish. Its skin is covered with a distasteful slime and its bright colors warn predators not to touch it. Small groups live inshore on silt-covered seabeds among coral and rubble. Most members of the dragonet family (Callionymidae), to which it belongs, are colored to match their surroundings. It is a popular aquarium fish but is very difficult to maintain. Shrimp gobies share their sandy burrows with snapping shrimp belonging to the genus Alpheus. The shrimp have strong claws and excavate and maintain the burrow, while the gobies have good eyesight and act as a lookout at its entrance. The yellow shrimp goby has bulging, high-set eyes, thick lips, and two dorsal fins. Although the usual coloration is yellow with faint, dusky bands, it can also be grayish white. This species lives in sandy areas of shallow lagoons and bays.

Tropical waters of Indian Ocean and southwestern Pacific

DISTRIBUTION

Unicornfish are so called because many have a hornlike projection on their forehead. However, the bignose unicornfish just has a rounded bulbous snout. At the base of the tail are two pairs of fixed, bony plates that stick out sideways like sharp knives, and the fish can inflict a serious wound on a potential predator. These blades are characteristic of surgeonfish (Acanthuridae), the family to which unicornfish belong. Usually dark with blue streaks, the bignose unicornfish can pale instantly to a silvery gray. This often happens when the fish is being cleaned by a cleaner wrasse (see p.365). It favors steep reef slopes where it can feed on zooplankton in the open water.

BONY FISHES

365

ORDER PERCIFORMES

Great Barracuda Sphyraena barracuda LENGTH

Up to 61/2 ft (2 m) WEIGHT

Up to 110 lb (50 kg) DEPTH

0–330 ft (0–100 m) DISTRIBUTION

Tropical and subtropical waters

worldwide

Barracuda are fast-moving predators with needle-sharp teeth and an undeserved reputation for ferocity. The great barracuda has a long, streamlined body with the second dorsal fin set far back near the tail. This fin arrangement, along with a large, powerful tail, allows it to stalk its prey and then accelerate forward at great speed. Large individuals in frequently dived sites will often allow divers to approach closely. Very occasionally a lone fish may attack a diver if it mistakes a hand or shiny watch for a silvery fish. Eating even small amounts of barracuda can result in ciguatera poisoning, caused by toxins accumulated from its food. GREAT BARRACUDA SKULL

Barracuda have flat-topped, elongated skulls with large, powerful jaws and knifelike teeth.

BARRACUDA SHOAL

While adults are normally solitary, juvenile great barracuda often swim together in large shoals in sheltered areas for protection.

ORDER PERCIFORMES

Atlantic Mackerel Scomber scombrus LENGTH

Up to 24 in (60 cm)

long front teeth

ORDER PERCIFORMES

Northern Bluefin Tuna Thunnus thynnus LENGTH

WEIGHT

Up to 15 ft (4.5 m)

Up to 71/2 lb (3.5 kg)

WEIGHT

DEPTH

Up to 1,500 lb (680 kg)

0–650 ft (0–200 m)

DEPTH

DISTRIBUTION Temperate waters of north Atlantic, Mediterranean, and Black Sea

0–9,900 ft (0–3,000 m) Northern and central Atlantic and Mediterranean

swimming and is one of the fastest bony fish, attaining speeds of at least 43 mph (70 km/h). The pectoral, pelvic, and first dorsal fins can be slotted into grooves to further streamline the torpedo-shaped body. To provide for long-distance, sustained swimming, the fish has large amounts of red muscle, which has a high fat content and can store oxygen. Other, similar species of bluefin tuna occur in the Pacific Ocean and southern parts of the Atlantic Ocean.

ORDER PERCIFORMES

Atlantic Sailfish Istiophorus albicans LENGTH

Up to 10 ft (3.2 m) WEIGHT

Up to 130 lb (60 kg) DEPTH

0–650 ft (0–200 m) DISTRIBUTION Temperate and tropical waters of Atlantic and Mediterranean

DISTRIBUTION

dark lines on back

The northern bluefin tuna is one of the world’s most valuable commercial fish and is heavily overexploited. Like mackerel, it is designed for high-speed silvery belly

OCEAN LIFE

The Atlantic mackerel is designed for fast swimming. It has a torpedo-shaped, streamlined body, small dorsal fins, close-fitting gill covers, and small, smooth scales. In the summer, large shoals feed close inshore, voraciously preying on small fish and straining plankton with their gills. From March to June, they lay their floating eggs in habitual spawning areas, the eggs hatching after a few days. In winter, the fish move into deeper water offshore and hardly feed. Several separate stocks exist within the north Atlantic, all of which are commercially exploited.

Like swordfish and marlin, the Atlantic sailfish has its upper jaw extended into a long spear. This is used to slash through shoals of fish, stunning and maiming them. It has a huge sail-like dorsal fin, which is used in displays, but is folded away for fast swimming. A similar sailfish occurs in the Pacific and may be the same species.

366

ANIMAL LIFE ORDER PLEURONECTIFORMES

European Plaice Pleuronectes platessa LENGTH

Up to 3 ft (1 m) WEIGHT

Up to 15 lb (7 kg) DEPTH

0–655 ft (0–200 m) DISTRIBUTION Arctic Ocean, northeastern Atlantic, Mediterranean, and Black Sea

This species is the most important commercial flatfish for European fisheries. Heavy fishing, however, has resulted in a progressive reduction in

ORDER PLEURONECTIFORMES

Common Sole Solea solea LENGTH

Up to 28 in (70 cm) WEIGHT

the size and age of fish landed. It is a typical oval-shaped flatfish with long fins extending along both edges of its thin body. Flatfish have both eyes on one side of their body and are either “right-eyed” or “left-eyed.” Plaice are right-eyed: they lie on the sea bed with their left side down. Their upward-facing right side is brown with orange or red spots. Plaice spend the day buried in the sand, emerging at night to feed on shellfish and crustaceans, which they crush using special teeth in the throat (pharyngeal teeth).Young plaice are also expert at nipping off the breathing siphons of shellfish that they spot sticking up out of the sand. Like all flatfish, the common sole starts life as a tiny larval fish floating near the surface. As it grows, it gradually undergoes a radical metamorphosis. The eye on the left side moves around the head to join the eye on the right and the body starts to flatten. When it is about a

ORDER TETRADONTIFORMES

Scrawled Filefish Aluterus scriptus LENGTH

Up to 31/2 ft

(1.1 m) WEIGHT

Up to 51/2 lb

(2.5 kg) 6–400 ft (2–120 m)

DEPTH

Tropical and subtropical waters of Atlantic, Pacific, and Indian oceans

DISTRIBUTION

month old, it settles on the sea floor with its eyeless side facing down. The skin on the underside stays white but the upper side develops pigment. Although common sole can live to be nearly 30 years old, they are a valuable food fish and most are caught when only a few years old.

Beautiful blue, irregular markings like a child’s scribbles give this reef fish its name. Filefish are closely related to triggerfish (see below, left), but are thinner and, except for the scrawled filefish, usually smaller. This large species has one large and one tiny spine on its back over the eyes. The fish uses these spines to help wedge itself into crevices for safety.

Up to 61/2 lb (3 kg) DEPTH

0–500 ft (0–150 m) DISTRIBUTION Temperate waters of northeastern Atlantic, Baltic, Mediterranean, and Black seas

Common sole are masters of camouflage and can subtly alter their color to match the sea bed on which they lie. The basic grayish brown color can be lightened or darkened and the pattern of darker splotches changed. Sole have a rounded snout and a semicircular mouth and their head is fringed with short filaments, giving them an unshaven appearance.

ORDER TETRADONTIFORMES

Spotted Boxfish Ostracion meleagris LENGTH

Up to 10 in (25 cm) ORDER TETRADONTIFORMES

Titan Triggerfish Balistoides viridescens LENGTH

Up to 30 in (75 cm) WEIGHT

Not recorded DEPTH

3–160 ft (1–50 m) Tropical reefs of Red Sea, Indian Ocean, and southwestern Pacific

OCEAN LIFE

DISTRIBUTION

The titan triggerfish is also known as the mustache triggerfish due to a dark line above its lips. It has large, strong front teeth and strong spines in its first dorsal fin. The first and longer spine can be locked in an upright position and released by depressing the second smaller “trigger” spine. This allows the fish to jam itself into a reef crevice, where it can rest safely, away from potential predators. The titan triggerfish preys on shellfish and crustaceans, which it crunches up

using its tough mouth and teeth. It can even make a meal of sea urchins by flipping them over and biting them on their vulnerable underside, where the spines are shorter.

WEIGHT

Not recorded DEPTH

3–100 ft (1–30 m) DISTRIBUTION Tropical reefs in Indian Ocean and South pacific, possibly extending to Mexico

PROTECTIVE PARENT In the breeding season, titan triggerfish dig a nest in a sandy patch of coral rubble using their mouth as a water jet. The female lays her eggs in the nest and one or both of the parents remains nearby to guard it. Normally a wary fish, parent titan triggerfish will attack divers that come too close to the nest and can inflict severe bites that need medical attention.

Instead of a covering of scales, all boxfish are protected by a rigid box of fused bony plates under the skin. This means they cannot bend their body and must swim by beating their pectoral fins. A large tail gives some propulsion and is also used to help steer them like a rudder. Male spotted boxfish are more colorful than the females, which are brown with light spots. These fish secrete a poisonous slime from their skin that protects them from predators.

BONY FISHES ORDER TETRADONTIFORMES

Ocean Sunfish Mola mola LENGTH

Up to 13 ft (4 m) WEIGHT

Up to 5,000 lb (2,300 kg) DEPTH

0–1,600 ft (0–480 m) DISTRIBUTION Tropical, subtropical, and temperate waters worldwide

ORDER TETRADONTIFORMES

Star Pufferfish Arothron stellatus LENGTH

Up to 4 ft (1.2 m) WEIGHT

Not recorded DEPTH

10–200 ft (3–60 m) DISTRIBUTION

Tropical reefs in Indian Ocean and

south Pacific

Compared with most other pufferfish, the star pufferfish is a relative giant. Its black-spotted skin is covered in small prickles and, if threatened, it will swallow water and swell up to an even larger size. At night, it searches out hard-shelled reef invertebrates and crushes them with powerful jaws that have fused, beaklike teeth.

ORDER TETRADONTIFORMES

Porcupinefish Diodon hystrix LENGTH

Up to 35 in (90 cm) WEIGHT

Up to 61/2 lb (3 kg) DEPTH

6–160 ft (2–50 m) Tropical and subtropical waters of Atlantic, Pacific, and Indian oceans DISTRIBUTION

HUMAN IMPACT

FUGU FISH Pufferfish produce tetrodotoxin, a lethal poison that is stronger than cyanide and for which there is currently no antidote. In spite of this, these fish are eaten in Japan as a delicacy called “fugu.” The poison is in the skin and some of the internal organs, and only licensed chefs, who have been specially trained, are permitted to prepare this dish. Pufferfish from the genus Takifugu are considered to be the best eating. A few people die every year from eating fugu, and the Emperor of Japan is officially barred from eating this delicacy for his own protection.

The ocean sunfish is the world’s heaviest bony fish and has a distinctive disklike shape. Instead of a caudal fin, it has a rudderlike structure (clavus) formed by extensions of the dorsal and anal fin rays, and it swims by flapping its tall dorsal and anal fins

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from side to side. Its common name comes from the fish’s habit of drifting in surface currents while lying on its side. It also swims upright with its dorsal fin sticking above the surface. The ocean sunfish has no scales, but its skin is very thick and stretchy. Like the porcupinefish (see below, left), to which it is related, the ocean sunfish has a single fused tooth-plate in each jaw, but it feeds mainly on soft-bodied jellyfish and other slow-moving invertebrates and fish. Females produce the most eggs of any bony fish, laying up to 100 million in the open ocean. Lone fish make grating noises with pharyngeal (throat) teeth, and this may help them to make contact with potential mates.

When a porcupinefish is frightened, it pumps water into its body until it looks like a prickly soccer ball. Few predators are large enough or brave enough to swallow a fish in this state. Left to itself, the porcupinefish deflates and its long spines lie flat against its body. During the day, it hides in caves and reef crevices, emerging at night to feed on hard-shelled invertebrates such as gastropod mollusks. prominent eye

OCEAN LIFE

erect spine

368

ANIMAL LIFE

Reptiles

HUMAN IMPACT

EXPLOITATION

DURING THE JURASSIC PERIOD, over

140 million years ago, reptiles were the largest animals in the oceans. Their place has since been taken by mammals, leaving few reptiles that are wholly marine. Of these, turtles are the most widespread, and sea snakes are the most diverse. Apart from the leatherback turtle, almost all are confined to warm-water regions, with the largest numbers around coasts and on coral reefs.

DOMAIN Eucarya KINGDOM Animalia PHYLUM Chordata CLASS Reptilia ORDERS 4 SPECIES About 7,723

All marine reptiles, apart from sea snakes, have a long history of exploitation by humans for food, skins, or shells. Turtles face the additional hazard of being accidentally caught in fishing nets, and numbers of all seven species have steeply declined. Marine turtles are now protected by international legislation. ILLEGAL SOUVENIRS

Anatomy

pointed scales (scutes)

Marine reptiles have several adaptations for life in the sea. Turtles have a low, streamlined shell, or carapace, and broad, flattened forelimbs that beat up and down like head wings. Marine lizards and crocodiles use their tails to provide most of the power when swimming, while most sea snakes have flattened tails that work like oars. Unlike land snakes, true sea snakes do not have enlarged belly scales, since they do not need good traction for crawling on land. All reptiles breathe air, and marine species have valves or flaps that prevent water entering their nostrils when they dive. Crocodiles also have a valve at the top of the throat, which enables them to open their mouths beneath the surface without flooding their lungs with water. Marine reptiles all need to expel excess salt. Sea snakes and crocodiles do this through salt glands in their mouths, while marine turtles lose salt in their tears. The marine iguana has salt glands located on its nose.

A saltwater crocodile’s teeth are constantly shed and replaced. During its lifetime, it may use over 40 sets.

Habitat Most marine reptiles live close to the shore, or return to it to breed. The only fully pelagic species are true sea snakes—those in the family Hydrophiinae. They remain in the open ocean for their entire lives. Sea snakes are also the deepest divers, feeding up to 330 ft (100 m) below the surface. Apart from the leatherback turtle, most marine reptiles depend on external warmth to remain active, which restricts them to tropical and subtropical waters. They also show striking variations in regional spread. This is particularly true of sea snakes: up to 25 species are found in some parts of the Indo-Pacific, but the Atlantic Ocean has none.

KEY

AT L A

Number of sea snake species

N

T

12–25 species I

C

2–12 species

OC

OCEAN

EAN

INDIAN

OCEAN LIFE

OCEAN

SOUT

Stuffed marine turtles—seen here on a beach in Peru—are still sold to tourists, despite being liable to seizure by customs officials. .

short rear flippers long front flippers

STREAMLINED SHELL

The hawksbill turtle has a tapering carapace with conspicuous scales, or scutes. Unlike most terrestrial tortoises, it cannot retract its head or legs inside its shell.

Food and Feeding

REPLACEMENT TEETH

PACIFIC

streamlined shell (carapace)

1 species

Most marine reptiles are carnivorous. Sea snakes typically feed on fish, although a few are specialized predators of fish eggs. They use their venom mainly in feeding, rather than for defense, killing their prey by biting it, and then swallowing it whole. Green turtles feed on seagrass when they become adult, while other marine turtles are carnivorous throughout their lives. The marine iguana is the only marine reptile that is a fully herbivorous. When young, it feeds on algae close to the waterline, but as an adult, it grazes seaweed growing on submerged rocks. Reptiles are cold-blooded (ectothermic), so they use less energy than mammals or birds. This means that they need less food, and can go for long periods between meals. Sea snakes, for example, can survive on just one or two meals a month.

HE RN OC EAN

SEA SNAKES WORLDWIDE

REEF SNAKE

Although diverse in the Indo-Pacific, sea snakes are absent from the Atlantic. Cold waters off southern Africa prevent them from spreading west.

A yellow-lipped sea krait searches for prey in a coral reef. Reefs are prime habitats for sea kraits, which generally live in shallow water.

GRAZING ON ALGAE

Marine iguanas have blunter heads than most lizards, enabling them to tear seaweed from rocks. Sharp claws act as anchors.

REPTILES

Reproduction

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REPTILE CLASSIFICATION

True sea snakes are the only reptiles that reproduce at sea. They give birth to live young (they are viviparous) after a gestation period of up to 11 months—much longer than most terrestrial species. All other marine reptiles, including sea kraits and marine turtles, lay their eggs on land. Many of these animals breed on remote beaches and islands, and the adults sometimes arrive simultaneously and in large numbers. The eggs are incubated by ambient warmth, and in crocodiles and turtles, the nest temperature determines the sex ratio of the hatchlings. Once the eggs have hatched, growth is fast, but mortality can be high. Parental care is rare in marine reptiles; female crocodiles are an exception, guarding their nests and carrying their young to water after they have hatched.

Three orders of living reptiles contain marine species. The fourth order includes only the tuataras, which are terrestrial. Snakes make up the vast majority of marine reptiles. Others, such as wart snakes and terrapins, live in fresh water, occasionally entering the sea. TURTLES AND TORTOISES Order Chelonia About 300 species

Seven turtle species are exclusively marine. Typical marine turtles (six species) have a hard carapace. The separately classified leatherback turtle has a rubbery carapace. SNAKES AND LIZARDS Order Squamata 7,400 species

About 70 species of snakes live in salt water. True sea snakes, belonging to the

subfamily Hydrophiinae, spend their lives at sea, while sea kraits (members of the family Elapidae) breed on land. Seagoing lizards are all semiterrestrial; only one species, the marine iguana, gets all its food offshore. CROCODILES AND ALLIGATORS Order Crocodilia 23 species

Only the American crocodile and the saltwater crocodile live in both fresh water and the sea. Crocodilians usually feed at the surface, rarely diving more than a few yards when at sea.

NEST IN THE SAND

After excavating a nest, a female leatherback lays her eggs. Turtle eggs are almost spherical, and have soft, leathery shells, which tear open when they hatch.

MARINE ADAPTATIONS

Thanks to their low metabolic rate, marine reptiles can remain underwater for long periods. This young saltwater crocodile is lurking on the seabed off New Guinea.

OCEAN LIFE

370

ANIMAL LIFE ORDER CHELONIA

Green Turtle Chelonia mydas LENGTH 21/2 –31/4 ft (0.8–1 m) WEIGHT 140–290 lb (65–130 kg)

Open sea, coral reefs, coasts

HABITAT

DISTRIBUTION

Tropical and temperate waters

worldwide

Elegantly marked and very effectively streamlined, this species is the most common turtle in subtropical and tropical waters, where it is often seen in eelgrass beds and on coral reefs.

ORDER CHELONIA

Hawksbill Turtle Eretmochelys imbricata LENGTH

21/2 –31/4

ft

(0.8–1 m) WEIGHT 100–165 lb (45–75 kg)

Coral reefs and coastal shallows

HABITAT

DISTRIBUTION

worldwide

Tropical and warm-temperate waters

Its color varies from green to dark brown, but its scales and shell plates (scutes) are lighter where they meet, giving it a distinctive, checkered pattern. Like all marine turtles, it has front flippers that are long and broad and beat up and down like wings. They provide the power for swimming, while the much shorter rear flippers act as stabilizers.Young green turtles are carnivorous, eating mollusks and other small animals, but the adults feed mainly on eelgrass and algae—a diet that keeps them close to the coast. Green turtles breed on isolated beaches, and they are remarkably faithful to their nesting sites. To reach them, some make journeys of more than 600 miles (1,000 km), navigating

their way to remote islands that may be just a few miles across. They mate in the shallows, and the females then crawl ashore after dark to dig their nests and lay eggs. Green turtles lay up to 200 eggs, burying them about 30 in (75 cm) beneath the sand. The eggs take about 6–8 weeks to hatch. All the young emerge simultaneously and scuttle for the safety of the waves. The green turtle has been hunted for centuries, mainly for food, and its numbers have declined significantly. Conservation measures include protection of the turtles’ nest sites, so that the young have a better chance of reaching the sea.

Named after its conspicuous beaked snout, the hawksbill has a carapace with a raised, central keel and pointed shell plates (scutes) around its rear margin. It lives in warm-water regions, feeding on sponges, mollusks, and other sedentary animals, and rarely strays far from shallows and coral reefs. It is less migratory than other marine turtles, breeding at low densities all over the tropics instead of gathering at certain beaches. On land, it has a distinctive gait, moving its flippers

in diagonally opposite pairs—other marine turtles move their front flippers together—the same action they use when swimming. The hawksbill is the chief source of tortoiseshell—detached, polished scutes. Despite being classified as Critically Endangered by the IUCN, hawksbills are often killed and stuffed when young to be sold as curios, particularly in Southeast Asia. Attempts at farming these turtles have not been successful.

EARLY LIFE After hatching while buried in the sand, the young turtles use their front flippers to dig toward the surface. They then make a dash for the sea, trying to avoid becoming a meal for waiting predators, including birds, crabs, snakes, and ants.Very little is known about their early life, as young green turtles are rarely observed in the wild, but it is certain that they face many predators in the sea. Their growth rate is known to average more than 11 lb (5 kg) per year.

ORDER CHELONIA

Loggerhead Turtle Caretta caretta 21/4 –31/4 ft (0.7–1 m)

LENGTH

165–350 lb (75–160 kg)

WEIGHT

Open sea, coral reefs, coasts

HABITAT

DISTRIBUTION

Tropical and warm temperate waters

worldwide

OCEAN LIFE

After the leatherback (opposite), the loggerhead is the second-largest marine turtle. It has a blunt head, powerful jaws, and a steeply domed carapace. It hunts and eats hard-bodied animals, such as crabs, lobsters, and clams. This species takes about 30 years to mature and breeds every other year.

REPTILES ORDER CHELONIA

Leatherback Turtle Dermochelys coriacea 41/4 –6 ft (1.3–1.8 m)

LENGTH

WEIGHT

Up to 2,000 lb

(900 kg) HABITAT

Leatherbacks breed mainly in the tropics, on steeply sloping sandy beaches, laying up to nine clutches of eggs in each breeding season. Unusually for a reptile, the leatherback turtle can keep its body warmer than its surroundings, thanks partly to the thick layer of insulating fat beneath its skin. This

allows it to wander much more widely than other turtles, reaching as far north as Iceland and almost as far south as Cape Horn. Individuals may roam huge distances—one leatherback tagged off the coast of South America was later found on the other side of the Atlantic, 4,200 miles (6,800 km) away.

Open sea

Tropical, subtropical, and temperate waters worldwide DISTRIBUTION

carapace with parallel ridges

large head on short neck

Kemp’s Ridley Turtle Lepidochelys kempi 20–35 in (50–90 cm)

LENGTH

55–90 lb (25–40 kg)

WEIGHT

HABITAT

Coral reefs,

coasts DISTRIBUTION Caribbean, Gulf of Mexico, occasionally as far north as New England

Also known as the Atlantic Ridley turtle, this is the smallest marine turtle, and also the most threatened, largely as a result of its unusual

THROAT SPINES The leatherback’s throat contains dozens of backward-pointing spines that prevent jellyfish from escaping before they are completely swallowed. These endangered turtles often die after eating discarded plastic bags, which they mistake for jellyfish. JELLYFISH TRAP

The leatherback’s throat spines can be over 1/ in (1 cm) long. They are regularly replaced 2 during the animal’s life.

The leatherback is the world’s largest marine turtle. Its carapace has a rubbery texture, having no hard plates, and has a tapering, pearlike shape. Its head is not retractable, and the leatherback is unique among turtles in having flippers without claws. It spends most of its life in the open sea, returning to the coast only when it breeds. It feeds on jellyfish and other planktonic animals, and while it gets most of its food near the surface, it can dive to depths of 3,300 ft (1,000 m).

ORDER CHELONIA

371

breeding behavior. Unlike most marine turtles, Kemp’s Ridleys lay their eggs by day, and the females crawl out of the sea simultaneously, during mass nestings called arribadas (Spanish for “arrivals”). At one time, these nestings took place throughout the turtle’s range, but because the eggs were laid in such large concentrations in daylight, they were easy prey for human egg-harvesters and natural predators. Today, the vast majority of Kemp’s Ridleys breed on a single beach in Mexico, where their nests are protected. These turtles were also often caught as bycatch in shrimp nets, but turtle excluding devices (TEDs) fitted to nets have helped to reduce

this threat. Several weeks after an arribada, young Kemp’s Ridleys emerge from their eggs in the thousands to make the dangerous journey down the beach and into the relative safety of the sea. The adults are carnivorous bottomfeeders that mainly hunt crabs. They have an unusually broad carapace, and their small size makes them agile swimmers. The carapace changes color with age: yearlings are often almost black, while adults are light olive-gray. A closely related species, the olive Ridley turtle (L. olivacea), lives throughout the tropics. It is much less endangered than the Kemp’s Ridley, thanks to its wider distribution.

ORDER CHELONIA

Flatback Turtle Natator depressus LENGTH 31/4 –4 ft (1–1.2 m) WEIGHT

Up to 190 lb

(85 kg) HABITAT

Coasts,

shallows DISTRIBUTION North and northeastern Australia, New Guinea, Arafura Sea

Named after its carapace, which is only slightly domed, the flatback has the most restricted distribution of any marine turtle. It lives in shallow waters between northern Australia and New Guinea, reaching south along the Great Barrier Reef. When adult, it is largely carnivorous, feeding on fish and bottom-dwelling animals such as mollusks and sea squirts. Despite their restricted range, adult flatbacks may swim over 600 miles (1,000 km) to reach nesting beaches. Females dig an average of three nests each time they breed and lay a total of about 150 eggs. The young feed at the surface on planktonic animals. Instead of dispersing into deep oceanic water, like the young of other turtle species, they remain in the shallows over the continental shelf.

OCEAN LIFE

HAWKSBILL TURTLE

This turtle owes its common name to its sharp, powerful beak, shaped like that of a bird of prey. The specimen photographed here, on a reef in the southern Red Sea, is holding a piece of soft coral, but its jaws are strong enough to detach even hard corals. It has two claws on each flipper.

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ANIMAL LIFE ORDER SQUAMATA

Yellow-lipped Sea Krait Laticauda colubrina LENGTH

31/4–10 ft

(1–3 m) WEIGHT

Up to 11 lb (5 kg)

Coral reefs, mangrove swamps, estuaries

HABITAT

DISTRIBUTION Eastern Indian Ocean and southwestern Pacific

This species is the most widespread of the sea kraits—a group of four closely related species that lay eggs on land, instead of giving birth at sea.

It has a pale blue body, marked with eye-catching dark blue rings, and distinctive yellow lips, which give it its common name. The yellow-lipped sea krait feeds on fish in shallow water, and although it has highly potent venom, it presents very little danger to humans because it is not aggressive and even when handled it rarely bites. Unlike many other marine snakes, sea kraits have large ventral scales that give them good traction when they crawl, allowing them to move around comfortably on land. During the breeding season, they come ashore in large numbers to mate and lay clutches of up to 20 eggs. Once they have hatched, the young make their way to the shallows, before dispersing along coasts and out to sea.

ORDER SQUAMATA

Yellow-bellied Sea Snake Pelamis platurus 31/4–5 ft (1–1.5 m)

LENGTH

WEIGHT

Up to 3 lb

(1.5 kg) HABITAT

Open water

Tropical and subtropical waters in Indian Ocean and Pacific

DISTRIBUTION

This boldly striped yellow-and-black snake has venom that is more toxic than that of a cobra. It is also the world’s most wide-ranging snake and

ORDER SQUAMATA

Beaked Sea Snake Enhydrina schistosa 31/4–5 ft (1–1.5 m)

LENGTH

WEIGHT

Up to 41/2 lb

(2 kg) Shallow inshore waters

HABITAT

Indian Ocean and western Pacific, from Persian Gulf to northern Australia

DISTRIBUTION

Notoriously aggressive and readily provoked, this widespread species is responsible for nine out of every ten deaths from sea-snake bites. Light gray with indistinct blue-gray bands, it has a sharply pointed head, slender body, HUMAN IMPACT

OCEAN LIFE

DEADLY VENOM The beaked sea snake’s bite contains enough venom to kill 50 people—about twice as many as the most venomous terrestrial snakes, such as the king cobra or death adder. Most of the snake’s human victims are bitten when wading or fishing in muddy water, although no reliable records exist of the numbers killed every year. However, its deadly venom does not protect this snake from being caught in shrimp-trawling nets. This hazard affects many sea snakes, but the beaked sea snake is particularly susceptible because it lives in shallow water and eats shrimp.

one of the very few that lives in the surface waters of the open ocean. Its distinctive colors warn that it is poisonous, protecting it from many predators. It feeds on small fish trying to shelter in its shade, swimming forward or backward with equal ease to grab them with its jaws. Although its fangs are tiny, its potent venom occasionally causes human fatalities. At sea, these snakes may form vast flotillas hundreds of thousands strong, and after storms, they may be washed up on beaches that lie far outside their normal range. However, the species has never managed to colonize the Atlantic Ocean, because cold currents stand in its way.Yellow-bellied sea snakes give birth to up to six young each time they breed.

and paddlelike tail. Its fangs are less than 1/5 in (4 mm) long, but its jaws can gape widely to accommodate large prey. It feeds mainly on catfish and shrimp. swimming near the bottom in shallow, murky water, in coastal waters, mangrove swamps, estuaries, and rivers, locating its victims by smell and touch. Like all fish-eating snakes, it waits until its prey has stopped struggling, before turning it so that it can be consumed head-first. Beaked sea snakes give birth to up to 30 young each time they breed, but their mortality is high, and only a small proportion of the young survive to become parents themselves. Despite their venom, these snakes are eaten by inshore predators, such as fish and estuarine crocodiles.

375 ORDER SQUAMATA

Turtle-headed Sea Snake Emydocephalus annulatus 2–4 ft (60–120 cm)

LENGTH

WEIGHT

Up to 3 lb (1.5 kg)

Coral reefs and coral sand banks

HABITAT

DISTRIBUTION Indian Ocean and Pacific, from northern Australia to Fiji

This Australasian sea snake is highly notable for its color variation, and also for its highly specialized lifestyle as a predator of fish eggs. The color it most commonly takes is a plain blue-gray, which is found throughout its range. A striking ringed form lives in some parts of the Great Barrier Reef, while a rarer, dark or melanistic form is found on isolated reefs farther

east in the Coral Sea. The turtleheaded sea snake moves slowly among living corals, methodically searching for egg masses either glued to the coral’s branches or laid directly on the coral sand. When it finds an egg mass, it scrapes the eggs off with an enlarged scale on its upper jaw, which works like a blade. In most cases, parent fish leave the eggs unguarded, so the snakes can feed unhindered, but some species— such as damselfish—guard their eggs aggressively and try to keep the snakes away. Little is known about this snake’s reproductive habits, apart from the fact that the females give birth to live young. In keeping with their lifestyle, turtle-headed sea snakes have tiny fangs (less than 1/32 in [1 mm] long) and they rarely try to bite. Their venom is one of the weakest of any sea snake, and instead of striking back at predators, they react to danger by disappearing into crevices in the reef.

ORDER SQUAMATA

Olive Sea Snake Aipysurus laevis LENGTH

3–7 ft (1–2.2 m)

WEIGHT

Up to 61/2 lb

(3 kg) Coral reefs, coastal shallows, estuaries

HABITAT

DISTRIBUTION Eastern Indian Ocean and western Pacific, from western Australia to New Caledonia

ORDER SQUAMATA

Leaf-scaled Sea Snake LENGTH

Up to 2 ft (60 cm)

WEIGHT

Up to 1 lb

(0.5 kg) Coral reefs and coral sand banks

HABITAT

DISTRIBUTION

reefs)

Timor Sea (Ashmore and Hibernia

OCEAN LIFE

Aipysurus foliosquama

This fish-eating snake has one of the most restricted ranges of any sea snake, being confined to a group of remote coral reefs about 185 miles (300 km) off the northwest coast of Australia. It is marked with contrasting bands or rings and gets its name from the characteristic shape of its dorsal scales. It lives in shallow water and rarely dives deeper than about 33 ft (10 m). Although venomous, it is rarely aggressive. Female leaf-scaled sea snakes are larger than the males and give birth to live young.

Plain brown or olive-brown above, with a paler underside, this common sea snake is one of six closely related species found in the reefs and shallow coastal waters of northern Australasia. Like its relatives, it has a cylindrical body, a flattened tail, and enlarged ventral scales—a feature normally found in snakes that spend some or all of their life on land. However, it is fully aquatic, hunting fish among the crevices and recesses of large corals. Instead of roaming throughout a reef, it often stays in the same small area of coral, rarely venturing into open water except after dark. Olive sea snakes give birth to live young, producing up to five finger-sized offspring after a gestation period of nine months. Unlike the adults, the young are dark in color, with a boldly contrasting pattern of lighter bands. This is gradually lost as they become mature. Olive sea snakes are naturally inquisitive and often approach divers. They have short fangs and bite readily if provoked. Their venom is toxic and has been known to be fatal.

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EQUIPPED TO GRIP

An adult marine Iguana sprawls on the sand, displaying the broad feet and long claws it uses to grip submerged rocks while it tears off mouthfuls of food.

ORDER SQUAMATA

Marine Iguana Amblyrhynchus cristatus LENGTH Up to 5 ft (1.5m), but often smaller WEIGHT Females (11/8 lb) 500 g; males 31/3 lb (1.5 kg), sometimes larger HABITAT DISTRIBUTION

Rocky coasts

Galapagos Islands

Restricted to the Galapagos Islands, this primeval-looking reptile is the only lizard that feeds exclusively at sea once it is an adult.The size and weight of this species varies between islands. It has a

OCEAN LIFE

spiky crest

blunt head with powerful jaws and a distinctive spiky crest that runs down its head, neck, and back.This lizard’s powerful claws help it clamber over rocks, while its tail propels its through water. It feeds on seaweeds and other algae.The young feed above the water, but adults dive up to 33 ft (10 m), and can hold their breath for over an hour. During the day, they spend their time feeding and sunbathing to raise their body temperature. During the breeding season, male marine iguanas engage in lengthy headbutting contests as they compete for mates. Females lay up to six eggs in the sand, and the young emerge after an incubation period of up to three months. Marine iguanas have many natural predators, including sharks and birds of prey, and have been severely affected by introduced animals, such as rats and dogs. blunt snout

PROFILE OF A GRAZER

Unlike predatory lizards, the marine iguana has blunt but powerful jaws. It secretes the surplus salt derived from its diet from glands near its nose.

SURVIVING THE COLD Although the Galapagos Islands are on the equator, they are bathed by the chilly Humboldt Current, which flows northward along the west coast of South America. Being a reptile, the marine iguana cannot generate its own body heat and needs special adaptations for feeding in these conditions. When it dives, its heart rate drops by about half,

helping it conserve energy to keep its core temperature higher than the water around it. At night, the iguanas often huddle together to keep themselves warm. BASKING IN THE SUN

When it returns to land, the marine iguana sprawls over rocks just above the surf to soak up warmth from the sun through its skin.

REPTILES ORDER SQUAMATA

Water Monitor Varanus salvator LENGTH

Up to 9 ft

(2.7 m) 35–75 lb (15–35 kg)

WEIGHT

Low-lying coasts, estuaries, rivers

HABITAT

DISTRIBUTION Indian Ocean, western Pacific, from Sri Lanka to the Philippines and Indonesia

An opportunistic predator with a wide-ranging diet, this is one of the largest lizards that regularly ventures into salt water. It has a long neck, strong legs, and a flattened tail, which lashes from side to side when it swims. It feeds on anything it can overpower, diving to catch prey in the shallows or running it down onshore. Like other monitors, it also feeds on carrion. In some places, it can often be seen on the outskirts of coastal villages, where it scavenges on discarded remains. Water monitors breed by laying eggs, which the female places at the end of a burrow. conspicuous markings when young

ORDER SQUAMATA

Mangrove Monitor Varanus indicus LENGTH

Up to 4 ft

(1.2 m) WEIGHT

Up to 22 lb

(10 kg) Mangrove swamps, coastal forests, estuaries, rivers

HABITAT

The water monitor has had human help in expanding its range. In the past, it was introduced by humans throughout the western Pacific as a source of food, and more recently, the species has been introduced into some Pacific islands as as a way of controlling rats. Water monitors lay up to a dozen eggs each time they breed and, like most lizards, their young hatch and develop without parental protection. flexible neck longer than head

DISTRIBUTION Western Pacific, from Micronesia to northern Australia

Similar in shape to the water monitor (left), this lizard has a comparable lifestyle, although it rarely swims far from the shore. Like all monitors, it has a long, supple neck and powerful clawed feet. Its tail is flattened laterally and is double the length of its body. They are very good swimmers and excellent climbers, hunting on the ground, in shallow water, and in trees. Fish make up a large part of their diet, although they eat a wide range of other food, including crabs, birds, other lizards, and even scavenged fishing bait.

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long, narrow head

ORDER CROCODILIA

American Crocodile Crocodylus acutus LENGTH

Up to 161/2 ft

(5 m) 400–1,000 lb (180–450 kg)

WEIGHT

Estuaries, open sea, coasts, lagoons

HABITAT

DISTRIBUTION Caribbean Sea, adjoining areas of Atlantic, Pacific coast of Central and South America

OCEAN WANDERER

The saltwater crocodile is a strong swimmer. It has been seen 600 miles (1000 km) from the nearest coast.

ORDER CROCODILIA

Saltwater Crocodile Crocodylus porosus LENGTH

Up to 23 ft (7 m)

Up to 2,200 lb (1 metric ton)

WEIGHT

Open sea, rivers, estuaries, coasts

HABITAT

DISTRIBUTION Indian Ocean, Pacific, from southern India to New Guinea and Australia

tail with vertical scutes

pointed jaws

ARMOUR PLATING

body slung between legs

The Saltwater Crocodile is protected by parallel rows of bony protruberances along its back.

It controls its body temperature by cooling down in water and warming up in the sun. Like other large crocodiles, the saltwater crocodile hunts by stealth, lurking close to the shore, hiding beneath the water with little more than its eyes and nose visible. When an animal comes within range, it bursts out of the water with explosive force, grabs its victim, and then drags it under until it drowns. Crocodiles cannot chew their food—instead, they tear it to pieces, digesting scales, skin, and even bones. Their natural prey includes birds, fish, turtles, and a wide variety of mammals, such as wild boar, monkeys, horses, and water buffalo. Females lay up to 90 eggs in a waterside mound, carrying their young to the water when they hatch. Saltwater Crocodiles are hunted in many parts of their range, making large specimens rarer than they once were.

protruding eyes with vertical pupils

powerful jaws

OCEAN LIFE

Also known as the estuarine or Indo-Pacific crocodile, this formidable predator is the world’s largest reptile, and is also one of the few crocodilians

that frequently swims far out to sea. Its power and ferocity are legendary, and it is thought to be responsible for more than 1,000 human deaths a year. The saltwater crocodile has powerful jaws housing teeth up to 5 in (13 cm) long. Its immensely tough skin is covered with thick scales. The scales on its back are armored with bony deposits called osteoderms, while its tail has a double row of upright bony plates (scutes). Its nostrils close when it dives, but it cannot exclude water from its mouth. Instead, it has a valve at the entrance to its throat, which opens only when it swallows food.

Of the four species of crocodile found in the Americas, this is the only one that—as an adult—is equally at home in both fresh water and the sea. When fully grown, it is olive brown, with a narrow-tipped snout, broad back, and a powerful, tapering tail. Its bony deposits (osteoderms) are smaller than those of other crocodiles. When young, American crocodiles feed on fish and small land animals, but adults often eat turtles, cracking them open in their jaws. Females bury their eggs in sand, laying about 40 every time they breed. Like all crocodiles, this species has been affected by being hunted for its skin, and by coastal development. Its stronghold is in Central America, but a few hundred individuals live in Florida, at the north of its range.

378

ANIMAL LIFE

Birds

MURRE DIVING

BIRDS THAT HAVE ADAPTED

to life at sea spend their lives in the air above the surface, KINGDOM Animalia in the upper layers of the open ocean, or PHYLUM Chordata along shorelines. Shore- (littoral) based birds CLASS Aves rarely range far from land, and some visit the ORDERS 29 coast only at certain times of year. Others SPECIES 9,500 are pelagic, often remaining at sea for months on end and returning to land only to breed. Unlike land birds, many pelagic sea birds breed in large colonies on islands and cliffs, deserting them when the breeding season ends. DOMAIN Eucarya

Using their wings as hydrofoils, common murres speed through icy water in search of fish. Members of the auk family, they are common in northern seas.

Anatomy There is no such thing as a typical sea bird, although pelagic birds share many adaptations for life at sea. These include webbed feet, highly waterproof plumage, and glands that get rid of excess salt. Most terrestrial birds have hollow, air-filled bones (an adaptation that helps to save weight), but in diving species, such as penguins, the bones are denser and the air spaces reduced. Some plunge-divers, including gannets and pelicans, have air sacs under their skin. These cushion the impact as they hit the water and help them to bob back to the surface with their prey. Compared to these marine species, shoreline birds show few specific adaptations for life in or near salt water but, like all birds, they have bills specialized for dealing with different kinds of food. streamlined bill narrow wings ideal for long-distance flight

FLYING DIVER

The northern gannet’s streamlined shape is typical of a plunge diver. Its nostrils open inside its bill, enabling it to keep out water when it hits the surface.

webbed feet

tubular, external nostril

food pouch

BILL ADAPTATIONS

Apart from waterfowl, most birds of the sea and shore are carnivores, with bills that are adapted for different kinds of animal prey. A pelican’s bill and pouch work like a scoop, while an albatross’s hooked bill can grip slippery prey, such as jellyfish. Sea eagles catch their prey with their talons, but then use their bills to tear it into pieces. Curlews have long bills that can probe for animals buried in mud.

hooked tip PELICAN

ALBATROSS

long bill can probe deep into estuarine mud

hooked bill

SEA EAGLE

CURLEW

OCEAN LIFE

Habitats Birds live throughout the world’s oceans and shorelines, from the equator to the poles. Less than 200 species are truly pelagic, meaning that they ply the oceans. These oceanic birds include albatrosses, which have wingspans of up to 11 ft (3.5 m), and much smaller species, such as shearwaters and terns. Although they feed on sea animals, their true habitat is the air: the sooty tern, for example, hardly ever rests on the water and may spend its first five years entirely on the wing. However, food is widely scattered in the open oceans, which is why the majority of sea birds live closer to land. Most diving sea birds feed in the shallow waters over continental shelves, while rocky coasts and mudflats are key habitats for waders and gulls. Estuaries are important habitats for coastal birds. Their muddy silt often harbors numerous worms and mollusks, accessible at low tide. In the tropics, mangrove swamps attract birds for the same reason; they also have the added bonus of trees, in which birds nest and roost.

COASTAL WADERS OCEAN WANDERER

The black-browed albatross travels long distances in search of good feeding grounds. Its diet includes crustaceans, fish, squid, and carrion.

Eurasian oystercatchers feed in a variety of coastal habitats, from rocky shores to mudflats. These birds are waiting for the tide to turn so that they can start to feed.

379

HUMAN IMPACT

SEA BIRDS UNDER THREAT

Feeding Methods brown pelican

33 ft (10 m)

13 ft (4 m) 160 ft (50 m) murre

cormorant

330 ft (100 m) 33 ft (10 m)

490 ft (150 m) adelie penguin

emperor penguin

820 ft (250 m)

MAXIMUM FEEDING DEPTHS

Plunge divers (left), such as the brown pelican, rarely reach more than a few yards beneath the surface. Deeper divers, such as the penguins, use their wings or feet to propel themselves, often staying under for several minutes.

DAWN PATROL

Trailing its beak in the water, a skimmer searches for food in the calm waters of a lagoon.

COLLATERAL DAMAGE

Caught in a fishing net, this cormorant is one of thousands of birds that drown every day. Diving birds have difficulty seeing plastic netting underwater and often become trapped.

OCEAN LIFE

660 ft (200 m)

Marine birds have evolved several ways of hunting their food. Most spectacular are the plunge divers—birds such as gannets, boobies, and brown pelicans—which slam into shoals of fish from heights of up to 100 ft (30 m). Diving sea birds also include many that operate from the surface, such as cormorants and penguins. Emperor penguins typically dive to 500 ft (150 m), but can descend to more than 870 ft (265 m)—the greatest depth for any bird. Many oceanic birds, such as albatrosses and petrels, hunt on the wing, snatching animals or scraps from the surface. Kleptoparasitic birds, such as frigatebirds, which harass other birds into disgorging their catch, also hunt on the wing. Coastal birds often probe for food in the shallows or along the tideline, but skimmers slice through the water, holding their lower bill underwater while in flight, a remarkable technique that works only if the surface is flat and calm.

The inexorable increase in fishing and shipping has had a significant impact on many coastal and marine birds. Sea birds are often harmed directly, becoming entangled in nets or caught in oil spills. They can also be harmed indirectly, when fishing reduces their food supply. Global warming poses yet another threat: changing sea temperatures can trigger major changes in the fish stocks on which birds feed.

380

ANIMAL LIFE

PACIFIC

N

A typical dispersing species, this bird nests in colonies scattered around the north Atlantic. When not breeding, it wanders as far south as the tropics, usually over continental shelves.

T

OCEAN I

C

PACIFIC

OC

OCEAN

EAN

summer distribution

INDIAN OCEAN

SOUTHERN OCEAN

winter distribution

RED PHALAROPE

AT L A

PACIFIC

N

T

OCEAN I

This migrant nests in the high Arctic, and overwinters in the southeast Pacific and eastern Atlantic. An extensive network of migration routes means that it is seen in many parts of the world.

C OC

EAN

Marine birds can range over a huge distance in their lifetime. Some, such as the northern gannet, disperse over wide areas of ocean, returning to isolated colonies to breed. The dispersal instinct of northern gannets is strongest in young birds and slowly declines during the four years that it takes them to mature sexually. From then onward, adults congregate at their colonies in spring and summer, dispersing again when their chicks have left the nest. Many other birds, such as the Red Phalarope, migrate between distinct summer and winter ranges. During their migrations, they can be seen “on passage” between their two homes. In the species profiles on the following pages, distribution maps show PACIFIC all the places where a species occurs—its summer and winter OCEAN ranges, as well as those regions it migrates through.

AT L A

NORTHERN GANNET

Dispersal and Migration

summer distribution INDIAN

winter distribution

OCEAN

SOUTHERN OCEAN

Breeding Once they reach adulthood, all sea birds have to come to land to breed. Some species nest on their own, but many form large colonies— often because secure nesting sites are few and far TREE NESTER between. Cliffs and islands are favorite locations, Frigatebirds are unusual among marine birds in that they nest as they offer the best protection from predatory in shrubs and tress. mammals. Fulmars and auks nest in burrows or fallen rocks, but most sea birds lay their eggs in the open, using little or no nesting material. Compared to terrestrial birds, they have small clutches. Cormorants often lay three or four eggs, but many MIXED COLONY other marine birds, such as albatrosses and puffins, Guanay cormorants, boobies, lay a single egg each year. These birds are often and brown pelicans nest in long-lived, but their low reproductive rate makes dense colonies on the desert them vulnerable to environmental problems, such islands off the coast of Peru—an area rich in fish. as oil spills or climate change.

MARINE BIRD CLASSIFICATION Of the world’s 27–29 bird orders, only two are exclusively marine: the penguins, and the albatrosses and petrels. A further eight orders contain a mixture of terrestrial, coastal, and marine species. WATERFOWL Order Anseriformes

LOONS Order Gaviiformes

177 species

5 species

Most species of ducks, geese, and swans live on, or near, fresh water and often move to coasts for the winter. A few are totally marine, and live in inshore waters.

These sleek, fish-eating birds dive from the water’s surface, propelling themselves with their feet. Loons are found mainly in the far north. They breed inland by fresh water, but often overwinter at sea. ALBATROSSES AND PETRELS Order Procellariiformes 142 species

OCEAN LIFE

KING PENGUIN

PENGUINS Order Sphenisciformes 18 species

These exclusively marine birds have lost the ability to fly. Most species are found in the Southern Ocean, but their range also extends northward in cold-current regions, reaching as far as the Galápagos Islands.

Totally marine birds occurring throughout all oceans, albatrosses and petrels return to land only to breed. Their external nostrils lend a good sense of smell. Most remain airborne for days, snatching food from the sea’s surface. GREBES Order Podicipediformes 23 species

These fish-eating birds have lobed feet set far back along their bodies. Most grebes live in freshwater habitats, but some migrate to coastal waters after the breeding season.

HERONS AND RELATIVES Order Ciconiiformes 119 species

These long-legged birds typically stalk their prey in shallow water or in marshy habitats. Most live inland, but several are found on coasts and coral reefs and in mangrove swamps. They often roost communally at night. PELICANS AND RELATIVES Order Pelecaniformes 65 species

This large group of sea birds includes pelicans, cormorants, tropicbirds, frigatebirds, and gannets. All are fish eaters, catching their food either by plunging into the water from the air or by diving from the surface. Found worldwide, they live on coasts and at sea and often feed in flocks. Some species, particularly cormorants, also frequent freshwater habitats. BIRDS OF PREY Order Falconiformes 333 species

Predatory birds, these species have hooked bills and sharp talons for snatching their prey. As a group, birds of prey are largely terrestrial, but some species specialize in catching fish, and can often be seen on coasts. They rarely venture far out to sea.

KELP GULL

WADERS, GULLS, AND AUKS Order Charadriiformes 385 species

This diverse order contains coastal and oceanic species, including many longdistance migrants. Diets are varied and feeding methods range from plunge-diving to shoreline scavenging. Many species are gregarious, feeding and nesting in colonies. KINGFISHERS AND RELATIVES Order Coraciiformes 230 species

These are primarily birds of forests or fresh water, although some species feed along coasts and inshore waters. They dive on prey from the air, taking off again directly after catching it, although they can swim.

BIRDS ORDER ANSERIFORMES

Brant Goose Branta bernicla 22–26 in (55–66 cm)

LENGTH

3–31/2 lb (1.3–1.6 kg)

WEIGHT

five eggs and raising a single brood each year. Like many birds in the High Arctic, their numbers undergo steep fluctuations. In mild summers, most of their goslings survive, but if conditions are unusually cold, very few young live long enough to migrate when summer comes to an end.

ORDER ANSERIFORMES

WEIGHT

20–28 in (50–71 cm)

23/4 –61/4 lb (1.2–2.8 kg)

WEIGHT

Shallow coasts, estuaries

HABITAT

DISTRIBUTION

Arctic Ocean, north Atlantic,

north Pacific

This heavily built duck is a common sight on Arctic coasts, where it dives to catch mollusks and crabs, cracking them open with its powerful bill. The females are mottled brown, while the males (below) are mainly black and white, with a pink breast and greenish neck. Common eiders breed in groups, building their nests close to the sea. After the breeding season, they move to more temperate zones in the south of their range for the winter months.

83/4 –10

WEIGHT 2–31/4 lb (0.85–1.45 kg)

lb

Rocky coasts, inshore waters

HABITAT

A compact bird with a gray body, black head, and black neck, the brant goose breeds in the High Arctic but winters on coasts at temperate latitudes—a pattern followed by many other wildfowl. Its preferred food is eelgrass, a marine plant that grows in shallow water, but in its winter quarters it also grazes in coastal fields. Brant geese nest in colonies in low-lying coastal tundra, laying up to

LENGTH

23–26 in (58–67 cm)

LENGTH

Coasts, estuaries, salt lakes

HABITAT

(4.0–4.5 kg)

DISTRIBUTION

Somateria mollissima

Tadorna tadorna

LENGTH 24–30 in (61–76 cm)

DISTRIBUTION Arctic (breeding); North America, northwest Europe, China, Japan (non-breeding)

Common Eider

Common Shelduck

Tachyeres pteneres

Estuaries, tundra, coastal grassland

ORDER ANSERIFORMES

ORDER ANSERIFORMES

Magellanic Flightless Steamer Duck

HABITAT

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Southern South America

This heavily built duck is one of three closely related species, all from South America, that have lost the ability to fly. Like other steamer ducks, it has mottled gray plumage, yellow legs, and a robust, yellow-orange bill. It feeds on mussels, crabs and other small animals, diving among kelp beds to find its food. If threatened, it paddles noisily across the water with its wings, a behavior known as “steaming.”

DISTRIBUTION

Europe, North Africa, Asia

With its brightly colored body and orange-red bill, the common shelduck is an eye-catching inhabitant of muddy shores. Normally seen in pairs, it feeds by dabbling in mud to collect small animals exposed by the falling tide. It nests in holes, and raises up to nine young each year. After breeding, common shelducks gather together to moult in flocks of up to 100,000 birds.

HUMAN IMPACT

EIDERDOWN To keep the eggs and young warm, female eiders line their nest with down feathers plucked from their breast. Eiderdown is a superb insulator and has long been used as a filling for clothes and bedding. It is still collected in Iceland, although demand has dwindled following the introduction of synthetic fibers. ORDER ANSERIFORMES

Red-breasted Merganser Mergus serrator LENGTH 20–23 in (52–58 cm) WEIGHT 21/4 –23/4 lb (1–1.25 kg)

Coasts, estuaries, lakes, rivers

HABITAT

DOWN OF THE COMMON EIDER

DISTRIBUTION Arctic and subarctic (breeding); temperate coasts (non-breeding)

OCEAN LIFE

This is one the most widespread sawbill ducks—ducks that have narrow beaks with serrated edges, like the teeth of a saw. All these birds dive for fish, using their specially adapted bills to grip their slippery prey. Like other sawbills, the red-breasted merganser has an elongated body, a long neck, and orange-red legs. Males (right) have a metallic green head and shaggy crest, while the female’s head is rust-colored, with a less flamboyant crest. These birds breed near fresh water, but spend the winter on coasts, where the water is less likely to freeze. Females build a nest in dense cover, or in a tree-hole, lining it with down. They lay up to 11 eggs, raising a single brood a year. Red-breasted mergansers are hunted in some parts of their range in order to protect fish stocks, although there is little evidence that they actually do much harm.

382

ORDER SPHENISCIFORMES

King Penguin Aptenodytes patagonicus 331/2 –371/2 in (85–95 cm)

HEIGHT

26–31 lb (12–14 kg)

WEIGHT

Rocky coasts, open ocean

HABITAT

Southern Ocean, subantarctic islands including Falkland Islands

DISTRIBUTION

This is the largest penguin found on shores outside Antarctica. Like its close relative the emperor penguin, it has a blue-black body with a white chest and conspicuous, yellow-orange markings on its head. Males and females look identical, and they share the task of incubating the single egg. Instead of building a nest, they cradle the egg on their broad webbed feet, where it is kept warm by a flap of skin. Their bodies are protected from the cold by short, densely-packed feathers and a thick layer of blubber. King penguins feed on fish and squid, diving to depths of over 650 ft (200 m) to hunt their prey. At one time, these birds were exploited commercially for their blubber, oil, and feathers, but today they are fully protected.

OCEAN LIFE

BREEDING OUT OF STEP King penguins have a breeding cycle found in no other sea bird. The cycle begins in November—the start of the southern summer—when the female lays her first egg. The chick takes 55 days to hatch, then stays with its parents for 11 months. Once the chick is independent, the female must complete her molt before laying again, this time in late fall. As a result, the king penguin’s breeding cycle takes 18 months and moves in and out of phase with the calendar year.

KING PENGUIN CHICKS

BIRDS ORDER SPHENISCIFORMES

ORDER SPHENISCIFORMES

Emperor Penguin

Chinstrap Penguin

Aptenodytes forsteri

Pygoscelis antarctica

43–45 in (110–115 cm)

28–30 in (71–76 cm)

77–88 lb (35–40 kg)

WEIGHT 61/2 –10 lb (3–4.5 kg)

Sea ice, rocky coasts, open ocean

Rocky coasts, open ocean

HEIGHT

HEIGHT

WEIGHT

HABITAT

DISTRIBUTION

Southern Ocean, Antarctica

The emperor is the world’s largest penguin and the only species that breeds in Antarctica during the southern winter. In shape and markings, it is very similar to the king penguin, but it can be over twice its weight. Rarely found outside Antarctic waters, it feeds among broken sea ice, diving to depths of up to 1,750 ft (530 m). It can remain underwater for as long as 20 minutes, and may travel up to 600 miles (1,000 km) in search of food. The emperor penguin breeds in scattered colonies on the ice itself. Adult females lay a single egg in early winter, and then transfer it to the male. During the winter darkness, while the females feed at sea, the males huddle together with their eggs balanced on their feet and protected within a fold of feathery skin. The incubation period lasts about two months. By the end of it, the males have lost about half their body weight. The females return when the chicks hatch, releasing the males, who head out to sea.

ORDER SPHENISCIFORMES

Little Penguin Eudyptula minor 16–18 in (40–45 cm) HEIGHT

WEIGHT

21/4 lb (1 kg)

Rocky and muddy coasts, open ocean HABITAT

DISTRIBUTION Southern Australia, New Zealand, Tasman Sea and Southern Ocean

HABITAT

away any larger penguins that attempt to nest nearby. The female lays two eggs, and her chicks fledge and set off for the sea by February or March, when the southern fall begins. Chinstraps feed almost entirely on krill, and their current population growth, like that of Antarctica’s krill-eating seals, may be linked to the decline of krill-eating baleen whales.

Southern Ocean, Antarctic Peninsula, subantarctic islands

DISTRIBUTION

chinstrap marking

Easily identified by the black line around its chin, the chinstrap penguin is one of the most abundant penguin species. Males and females look identical, with blue-black bodies, white undersides, and straight black bills. They live at sea for most of the year, feeding in open water north of the polar ice.When swimming at high speed, they often leap clear of the water, or “porpoise,” which allows them to breathe and coats their bodies with a layer of air bubbles, reducing friction with the water. In November, chinstraps return to their breeding colonies on ice-free shores in Antarctica and on islands in the Southern Ocean. Here, they make their nests by scraping together small stones to form a shallow cup. Chinstraps tend to be more aggressive than other penguins, particularly when breeding. They steal stones from their neighbors and chase

SAFETY AFTER DARK In some parts of their range— such as Phillip Island, near Melbourne—thousands of little penguins can be seen scrambling ashore as the light fades. This behavior protects them from most predators, although not from introduced mammals such as foxes and domestic dogs.

This is the smallest penguin, and it is also the only one that remains offshore during daylight, coming onto land after dark. It has a white underside, a gray-blue back and head, and no distinctive markings. During daylight, little penguins are often seen in small flotillas offshore, resting on the surface and periodically diving to catch fish.

ORDER SPHENISCIFORMES

Macaroni Penguin Eudyptes chrysolophus HEIGHT

271/2 in

(70 cm) WEIGHT

91/4 lb (4.2 kg)

Rocky coasts, open ocean

HABITAT

DISTRIBUTION Southern Ocean, Antarctic Peninsula, subantarctic islands, southern South America

Macaroni penguins are often seen together with a similar species of penguin, the rockhopper. However, macaronis are significantly larger and have distinctive flame-yellow crests that run above each eye and meet on the forehead. They are also found farther south, breeding on ice-free coasts on the Antarctic Peninsula. Their breeding colonies are extremely noisy, some containing over a million pairs spaced out just beyond pecking distance of each other. Macaroni penguins lay two eggs a year, and both parents help with incubation. Their reproductive rate is low, because only one nestling normally survives.

ORDER SPHENISCIFORMES

ORDER SPHENISCIFORMES

Magellanic Penguin

Jackass Penguin

Spheniscus magellanicus

Spheniscus demersus

HEIGHT

28 in (71 cm)

WEIGHT

12 lb

HEIGHT 24–28 in (60–70 cm)

(5.5 kg)

WEIGHT

Rocky coasts, open ocean

HABITAT

HABITAT

11 lb (5 kg)

Rocky coasts, open ocean

DISTRIBUTION Southern South America, Falkland Islands, south Atlantic and south Pacific

DISTRIBUTION Coastal waters of southern Africa, south Atlantic and southern Indian Ocean

One of two species of black-andwhite penguin from South America, the Magellanic penguin is identified by the two black bands across its breast (see below). It feeds in the cold waters that flow northward from the Southern Ocean, eating small, shoal-forming fish such as sardines. Like its close relative, the Humboldt penguin, it nests in burrows, raising up to two chicks each year.

Also known as the Cape penguin, the jackass is the only penguin that breeds in Africa. Physically, it bears a strong resemblance to the Magellanic penguin (see left) from South America, although it has a single black breast band rather than two. It feeds on small fish such as pilchards, sardines, and anchovies, and gets its name from its braying call, which may be heard onshore when it breeds. Jackass penguins nest in burrows, and in the past, many of their nesting sites were destroyed by farmers collecting their droppings, or guano, for use as fertilizer. Today, depletion of food stocks due to overfishing and oil spills are two major threats that they face, along with competition from fur seals for breeding sites. Their numbers are in sharp decline.

OCEAN LIFE

When feeding, they circle around small fish to concentrate them into a close-knit group, before swimming through the shoal and snapping them up. Unlike other penguins, they do not leave the water when they travel at speed. Little penguins usually nest in burrows or among fallen rocks, but may set up home in breakwaters and under houses and sheds. Each female lays a clutch of two eggs and raises up to two broods a year.

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EMPEROR PENGUINS

Emperor penguins are among the hardiest animals in the world, able to withstand blizzards on land and deep dives in the freezing waters of the Southern Ocean. Fast and agile swimmers, they can usually outrun and outmanoeuver the leopard seals that hunt them, although they are vulnerable when entering and leaving the water.

386

ANIMAL LIFE

ORDER PROCELLARIIFORMES

Black-footed Albatross Phoebastria nigripes 68–74cm (27–29in)

LENGTH

3–3.5kg (61/2 –73/4 lb)

WEIGHT

Open ocean, atolls, isolated islands

HABITAT

North Pacific, Johnston Island and Marshall Islands

DISTRIBUTION

This dark-coloured sea bird is often seen in summer off North America’s west coast. One of three species of albatross found in the north Pacific, its dark underwings distinguish it from the other two. It is fond of scavenging, and often follows trawlers and shrimping boats to catch discarded offal. Black-footed Albatrosses breed in colonies on islands in the central and western Pacific. Like other albatrosses, they perform elaborate courtship displays. All albatrosses are monogamous, pairing up to breed with the same partner each autumn.

HUMAN IMPACT

LONG-LINE FISHING The Black-footed Albatross is a frequent victim of long-line fishing, which involves trailing lines that carry thousands of baited hooks. Albatrosses swallow the bait and become caught. Long-line fishing is estimated to kill at least 300,000 sea birds of all kinds each year. VICTIM OF DROWNING

Albatrosses usually swallow their food whole, so long-line hooks become lodged in their stomachs and drag the birds underwater to drown.

ORDER PROCELLARIIFORMES

Short-tailed Albatross Phoebastria albatrus 84–94cm (33–37in)

LENGTH

ORDER PROCELLARIIFORMES

Light-mantled Sooty Albatross Phoebetria palpebrata 79–98cm (31–39in)

3–5kg (61/2 –11lb)

LENGTH

Remote islands (breeding); open ocean

WEIGHT

WEIGHT

HABITAT

Remote islands (breeding); open ocean

HABITAT

North Pacific, Tori Shima Island and Senkaku Islands

DISTRIBUTION

ORDER GAVIIFORMES

Great Northern Diver Gavia immer LENGTH 70–90cm (28–35in) WEIGHT 3–4.5kg (61/2 –10lb)

Freshwater lakes (breeding); coasts

OCEAN LIFE

HABITAT

DISTRIBUTION Northern North America, Greenland, Iceland, Europe, north Pacific, north Atlantic

This striking bird is best known for its haunting cry, which echoes across freshwater lakes during the summer breeding season. During the winter, the same bird is a common visitor in coastal waters, although at this time of year its black-and-white breeding

plumage is replaced by less eyecatching shades of brownish black and grey. Like other divers, it has a streamlined body, small wings, and webbed feet set far back – a feature that makes it clumsy on land. On water, it is far more graceful. It floats with its bill held at a characteristic upward slant and can dive to depths of over 75m (250ft) to catch fish – its principal food. During the summer months, Great Northern Divers usually live in pairs, carrying out spectacular courtship displays. When the breeding season comes to an end, they migrate to sheltered coasts, where there is less risk of icing. In North America, flocks of several hundred often gather on the Great Lakes, before heading south as far as the coast of Florida. In Europe, they winter on Atlantic coasts, dispersing as far south as Portugal.

2.5–4.5kg

(5–10lb)

Southern Ocean, isolated islands in south Atlantic and southern Indian Ocean

DISTRIBUTION

This north Pacific albatross almost became extinct during the early 1900s due to demand for its feathers. By 1950, only about 20 birds were left. Thanks to conservation measures, the population now stands at nearly 2,000, all breeding on remote islands in the far west of its range. Adults are mostly white, with black flight feathers, pink bills, and golden-yellow heads.

Together with its close relative the Sooty Albatross, this is one of two southern albatrosses that have sooty brown plumage, as opposed to white and black. The Sooty Albatross is brown all over, but the Light-mantled species has a pale grey nape and back – the feature that gives it its name. A graceful glider, it feeds on fish, squid, and crustaceans. It is also highly inquisitive and often follows ships. After spending the winter at sea, it returns to its breeding sites by August, the start of the southern spring. Female birds lay a single egg in early summer, and the chicks become independent about four months after they hatch – a relatively rapid development compared with that of the larger albatrosses.

387 ORDER PROCELLARIIFORMES

Wandering Albatross Diomedea exulans 1.1–1.35m (31/2 –41/2 ft)

LENGTH

8–11.5kg (18–25lb)

WEIGHT

Remote islands (breeding); open ocean

HABITAT

DISTRIBUTION Southern Ocean, south Atlantic, southern Indian and Pacific oceans

This legendary sea bird has the largest recorded wingspan of any bird, at up to 3.5m (111/2 ft). It is restricted to the windswept southern oceans, where it feeds mainly on squid, snatching its food from the surface of the water. It is capable of remaining airborne for weeks at a time and frequently follows ships, soaring over the waves on its stiff, outstretched wings. The Wandering Albatross takes up to 11 years to mature, and during that time it gradually loses its juvenile plumage, becoming all white except for black markings on the tips and trailing edges of its wings. These birds nest on remote islands, typically breeding in alternate years.

LONG INCUBATION Wandering Albatrosses build large, mound-like nests from mud, grass, and moss. Their single egg has one of the longest incubation periods of any egg, taking between 75 and 82 days to hatch. The solitary chick then remains in the nest for up to nine months, where it is fed by both its parents. During very severe weather, the chick may be left unattended for days at a time.

ORDER PROCELLARIIFORMES

Black-browed Albatross Thalassarche melanophrys 83–93cm (33–37in)

LENGTH

3–5kg (61/2 –11lb)

WEIGHT

Remote islands (breeding); open ocean

HABITAT

DISTRIBUTION Southern Ocean, south Atlantic, southern Indian and Pacific oceans

Also known as the Black-browed Mollymawk, this is the most numerous and widespread of the albatrosses. It is found from Antarctica to the edge of the tropics, and in places even further north. Its wings, back, and tail are greyish black, and it has a distinctive black brow above each eye. It feeds on fish, squid, octopus, and crustaceans, and is also a frequent ship-follower, congregating in large numbers when waste is thrown overboard. Black-browed Albatrosses breed on remote islands and take at least five years to become mature. They are among the few southern albatrosses that regularly cross the Equator – isolated sightings have been recorded as far north as the British Isles.

OCEAN LIFE

388

ANIMAL LIFE ORDER PROCELLARIIFORMES

Southern Giant Petrel

ORDER PROCELLARIIFORMES

Northern Fulmar Fulmarus glacialis

Macronectes giganteus

18–20 in (45–51 cm)

LENGTH

LENGTH 34–39 in (86–99 cm) WEIGHT

11/2 –2 lb (700–900 g)

WEIGHT

11 lb (5 kg)

Coasts, open sea; nests on ice-free coasts

Rocky coasts,

HABITAT

open sea

HABITAT

DISTRIBUTION North Pacific, north Atlantic, ice-free areas of Arctic Ocean

Often mistaken for a gull, this fulmar is actually a petrel and, like other petrels, has distinctive tubular nostrils. Common throughout northern waters, it is often seen flying over cliffs on its stiff, outstretched wings. Its weak feet make it clumsy on land, and its eyes are dark with a distinct brow ridge. Most northern fulmars in the Atlantic have white bodies and blue-gray upper wings, but in the Pacific many of the birds are much darker. Northern fulmars feed on

small animals at or near the sea’s surface, and they gather in large flocks to scavenge around fishing boats. They breed on exposed cliff ledges, with each female laying a single egg directly onto the rock. The incubation period is 52 days—almost twice as long as that in gulls of similar size. Despite its low reproductive rate, the northern fulmar has increased both in range and in numbers in recent years. It is exceptionally long-lived for its size, with ages of over 50 years recorded.

Southern hemisphere, from Antarctica as far north as the tropics DISTRIBUTION

Part-scavenger and part-predator, this large petrel is often seen on the fringes of penguin colonies or near the carcasses of dead seals and whales. It uses its powerful bill to tear apart carrion and to kill young birds. Most adults have a pale head and a dark grayish brown back, but some are almost completely white with scattered black flecks. tubular nostrils

ORDER PROCELLARIIFORMES

ORDER PROCELLARIIFORMES

Snow Petrel

Fairy Prion

Pagodroma nivea

Pachyptila turtur LENGTH 12–14 in (30–35 cm)

LENGTH

10–11 in (25–28 cm)

WEIGHT 9–16 oz (250–450 g)

WEIGHT

Rocky and ice-bound coasts

HABITAT

5–8 oz (150–225 g)

Islands (breeding); open ocean

HABITAT

DISTRIBUTION Antarctica, subantarctic islands, Southern Ocean

Despite its dainty appearance, the snow petrel is one of the world’s most southerly breeding birds. This entirely white petrel nests on ice-free cliffs in and near Antarctica, to within 680 miles (1,100 km) of the South Pole. It picks food from the surface of the sea, rarely straying far from the polar ice. Flocks of snow petrels are often seen sitting on icebergs.

DISTRIBUTION

ORDER PROCELLARIIFORMES

Bonin Petrel Pterodroma hypoleuca LENGTH

12 in (30 cm)

WEIGHT

8 oz (225 g)

Oceanic islands (breeding); open ocean

OCEAN LIFE

HABITAT

DISTRIBUTION

Northwestern Pacific

There are over two dozen species of Pterodroma petrels, mostly in tropical and subtropical regions, and these are often difficult to distinguish at sea. The Bonin petrel is a typical example from the northwestern Pacific, where it

nests on scattered islands westward from Hawaii. It has a small, short, slightly hooked bill and sharply pointed wings, and it is fast and agile as it speeds through the air just above the waves. It eats small planktonic animals, usually landing on the surface to feed. This petrel nests in burrows but has difficulty moving on land. To reduce the risk of attack from predators, the Bonin petrel generally returns to land at night, when it may deliver regurgitated food to its single chick. The parents share the task of egg incubation over about 49 days. On remote islands, petrel colonies can be decimated by introduced predators, such as rats and cats. This species is one that has been badly affected.

Southern Ocean and adjoining waters

A small, oceanic petrel, the fairy prion has a pale body and blue-gray upper wings with a distinct, M-shaped black band. It lives in flocks and feeds at night, using its bill to sieve planktonic animals from the water. It breeds on isolated coasts, laying a single egg either in a burrow or in a hollow deep among fallen rocks.

389 ORDER PROCELLARIIFORMES

Great Shearwater Puffinus gravis 18–21 in (46–53 cm)

LENGTH

13/4 –2 lb (800–900 kg)

WEIGHT

Oceanic islands (breeding); open ocean

HABITAT

DISTRIBUTION Atlantic Ocean, except off west coast of Africa south of Sierra Leone

This ocean-living sea bird is a wide-ranging migrant and is found across most of the Atlantic Ocean during the course of the year. It breeds in the far south, on some of the world’s remotest islands. One of these, Nightingale Island in the Tristan da Cunha group, is home to about four million birds. Great shearwaters have pointed wings with dark brown upper surfaces. Their undersides are much paler, making the birds look alternately black then white during their tilting flight. Sometimes vocal at sea, they wail and scream noisily from their burrows when breeding. These calls are thought to help incoming birds to locate their mates after dark.

ORDER PROCELLARIIFORMES

Short-tailed Shearwater Puffinus tenuirostris 16–17 in (41–43 cm)

LENGTH

ORDER PROCELLARIIFORMES

Wilson’s Storm Petrel Oceanites oceanicus LENGTH 6–71/2 in (15–19 cm)

1–11/2 oz (30–40 g)

WEIGHT

HABITAT Coasts, islands (breeding); open ocean

Worldwide except for north Pacific and extreme north Atlantic

DISTRIBUTION

a single chick. Fed on a rich diet of oily food, the chicks weigh more than their parents by the time they leave the nest. For several centuries, shearwater chicks have been harvested for their oil and meat. The practice continues today, although the numbers killed are now strictly controlled.

Little bigger than a sparrow, Wilson’s storm petrel is reputed to be the world’s most numerous ocean-going sea bird. It breeds in widely scattered colonies, and its total population is unknown but may exceed 20 million. At sea this bird may be difficult to distinguish from its close relatives, but its plumage is uniformly sooty brown, apart from a band of white at the base of its tail. When feeding, storm petrels

ORDER PROCELLARIIFORMES

Leach’s Storm Petrel Oceanodroma leucorhoa LENGTH 71/2 –81/2 in (19–22 cm) WEIGHT 11/2 –13/4 oz (40–50 g)

1–11/2 lb (500–700 g)

WEIGHT

Coasts, islands (breeding); open ocean

HABITAT

Open ocean, offshore islands

HABITAT

with its feet and occasionally settling on the water to rest. Leach’s storm petrels breed in colonies, laying a single egg and returning to their burrows at night with food for their hatched young. In the far north, some birds delay nesting until August to avoid the 24-hour daylight of the Arctic summer, during which they would be more vulnerable to predators.

DISTRIBUTION North Pacific, north Atlantic, coastal North America and Aleutian Islands

DISTRIBUTION North Pacific, southwestern Pacific around southern coast of Australia

Leach’s storm petrel is silent at sea, but it makes a high-pitched purring sound, interrupted by sharp whistles, in and near its nest. Unlike Wilson’s storm petrel (see above), this species breeds in the Northern Hemisphere. It migrates southward in late summer, roaming throughout the north Pacific and much of the Atlantic. Small and brownish black, with a sharply forked tail, it flies rapidly, changing direction frequently as it scans the water’s surface for food. It feeds on planktonic animals and small fish, pattering on the surface

Awkward and ungainly on land, the short-tailed shearwater is a tireless flier, skirting around most of the north Pacific during its annual migration. Like other shearwaters, it travels just inches above the waves in fast-moving flocks, interrupting its flight whenever it spots food. However, it has a narrower bill than other shearwaters, and its overall color is a dark, smoky brown. It nests in vast island colonies, each pair producing

MIGRATION

ORDER PROCELLARIIFORMES

June– August

September

Common Diving Petrel Pelecanoides urinatrix

April– May

LENGTH 8–10 in (20–25 cm)

October

4–41/2 oz (110–130 g)

WEIGHT

Coasts, islands (breeding); open ocean

HABITAT

November– March

DISTRIBUTION

and islands

Southern Ocean and adjoining waters

This stubby bird with pointed wings and pale blue feet is the Southern Hemisphere’s counterpart of the auklets (see p.399). Despite being unrelated, it shares the auklets’ fast, low flight and their feeding technique. Instead of searching for food on the wing, like other petrels, it dives, using its wings to swim. It frequently flies straight through waves, emerging with rapidly whirring wings on the other side. This species nests in burrows, returning to its nests after dark. There are three other similar-looking species, all found in southern seas.

OCEAN LIFE

The short-tailed shearwater has a unique figure-eight migration route, 20,800 miles (33,500 km) long, that takes advantage of prevailing winds. After laying eggs in November and December, the birds head north in April and May, reaching the Bering Sea by August. They then move south along North America’s west KEY coast, before returning to breeding area their breeding migration route colonies. wind direction

rarely settle on the water. Instead, they flutter their wings and patter the surface with their feet, pecking up planktonic animals. When food is abundant, they may suddenly appear in huge numbers then disappear with equal abruptness. Wilson’s storm petrel breeds as far south as Antarctica, digging a burrow with its bill and feet. It migrates northward when the southern summer comes to an end.

390

ANIMAL LIFE ORDER CICONIIFORMES

Gray Heron

ORDER CICONIIFORMES

Little Egret

Ardea cinerea

Egretta garzetta LENGTH

34–39 in (90–100 cm)

LENGTH

WEIGHT 31/2 –41/2 lb (1.6–2 kg)

WEIGHT

Estuaries, lagoons, coasts

HABITAT

HABITAT

22–27 in (56–65 cm)

11–16 oz (300–450 g)

Muddy coasts, mangrove swamps

DISTRIBUTION Europe, mainland Asia (except far north), Japan, Indonesia, Africa, Madagascar

DISTRIBUTION Southern Europe, Africa, southern Asia, Southeast Asia, Australasia

Commonly seen in fresh water, the gray heron also frequently visits shores, especially in areas where lakes and ponds freeze in winter. Tall, graybacked, and often immobile, it waits patiently for fish or other animals to come within range, then seizes them with a rapid jab of its daggerlike bill. On coasts, its feeding method restricts it to shallow water on rocky and low-lying shores, where it often follows the falling tide. Gray herons fly with slow wingbeats, their heads hunched into their shoulders and their legs trailing behind. They nest in trees, typically inland near water.

Pure white with black legs, a black bill, and bright yellow facial skin, the little egret is usually seen on its own or in scattered groups, wading quietly through shallow water on coasts. This bird feeds on fish and other shoreline animals that are disturbed by its approach. During the breeding season, both males and females grow long, lacy feathers on their heads and backs. They nest in trees, building flimsy nests out of sticks.

ORDER CICONIIFORMES

Pacific Reef Egret Egretta sacra 24–27 in (60–70 cm)

LENGTH

14–26 oz (400–750 g)

WEIGHT

Coastal and freshwater wetlands

HABITAT

Australasia, Pacific islands, western Pacific coast from Southeast Asia to Japan

DISTRIBUTION

This compact shoreline egret has two contrasting color forms, so different that they look like separate species. One form (or morph) is completely

ORDER PELECANIFORMES

Great Frigatebird Fregata minor 34–39 in (86–100 cm)

LENGTH

3–4 lb (1.4–1.8 kg)

WEIGHT

Coasts, islands (breeding); open ocean

HABITAT

Tropical regions in Indian Ocean and Pacific, sporadic in tropical Atlantic

DISTRIBUTION

ORDER PELECANIFORMES

OCEAN LIFE

Red-billed Tropicbird Phaethon aethereus LENGTH Up to 191/2 in (50 cm) excluding tail WEIGHT 11/4 –13/4 lb (600–800 g)

Coasts, islands (breeding); open ocean

HABITAT

DISTRIBUTION Eastern Pacific, Caribbean, tropical Atlantic, northeast Indian Ocean

The largest of the three species of tropicbird, this elegant sea bird spends most of its life flying over the open ocean, often hundreds of miles from land. From a distance the red-billed tropicbird resembles a dove, but for two highly distinctive tail streamers that flutter behind it as it flies. It feeds by plunge-diving, hovering to locate its prey before diving with half-folded wings into the sea. Despite being very buoyant, it seldom swims. Like other tropicbirds, it nests on remote coasts and oceanic islands and is rarely seen outside tropical waters.

white, with a pale yellow bill and yellow-gray legs. The other form has a similarly colored bill and legs, but its plumage is dark gray. The balance between the two forms varies. In some islands in the tropical Pacific the white form predominates, but in New Zealand, the overwhelming majority are gray. Pacific Reef Egrets forage alone or in small groups, feeding on small fish, crabs, and mollusks. When hunting, they hold their heads and bodies almost horizontally and often shade the water with their half-spread wings. Unlike most egrets, they frequently nest on the ground, among fallen rocks or in coastal caves, as well as in low-growing trees. With their extraordinarily long wings and slender bodies, frigatebirds are unrivaled experts at gliding flight. The five species all have glossy black plumage, strong, hooked bills, and small, webbed feet. The males also have a bright red throat pouch, which they inflate during courtship displays. Despite weighing less than a large gull, the great frigatebird has a wingspan of up to 71/2 ft (2.3 m), allowing it to glide for hours while making only the merest flick of its wings. As it flies, it observes other sea birds as they feed, then pursues them to steal their catch. Frigatebirds also hunt their own food, snapping it up from the sea’s surface. They nest in coastal bushes, where they make flimsy nests out of twigs.

BIRDS ORDER PELECANIFORMES

ORDER PELECANIFORMES

Brown Pelican

Northern Gannet

Pelecanus occidentalis

Morus bassanus

LENGTH

4–51/4 ft (1.2–1.6 m)

LENGTH 34–39 in (87–100 cm)

WEIGHT

73/4 –10 lb (3.5–4.5 kg)

WEIGHT 61/4 –7 lb (2.8–3.2 kg)

Coastal waters, estuaries, islands

HABITAT

DISTRIBUTION Pacific and Atlantic coasts of North and South America, Galápagos Islands

DISTRIBUTION

Eastern and western coasts of

north Atlantic

Commonly seen inshore and in harbors, the brown pelican is the heaviest sea bird that fishes by plunge-diving. Groups of birds often fish together, skimming over the waves before rising into the air, folding back their wings, and hitting the water with a spectacular splash. The pelican’s throat pouch balloons outward underwater, scooping up prey, which it then swallows at the surface.

This highly streamlined bird with its gleaming white body and black-tipped wings is the most striking plunge-diver in the north Atlantic. Northern gannets roam the seas with a distinctive pattern of flapping and gliding flight, attacking shoals of fish by diving from heights of up to 100 ft (30 m). They breed in crowded colonies on rocky islands and clifftops, laying a single egg each year. Juveniles take five years

ORDER PELECANIFORMES

Brown Booby Sula leucogaster LENGTH 25–30 in (64–76 cm) WEIGHT 11/2 –31/4 lb (0.7–1.5 kg)

Inshore waters, rocky coasts, islands

HABITAT

DISTRIBUTION Tropical oceans worldwide, except southeastern Pacific

Blue-footed Booby Sula nebouxii

sometimes diving into water less than 3 ft (1 m) deep. They nest in small colonies on offshore islands, laying their eggs on the ground.

30–33 in (76–84 cm)

LENGTH

21/4 –41/2 lb (1.5–2 kg)

WEIGHT

Inshore waters, rocky coasts, islands

HABITAT

to mature, gradually losing their brown plumage. During that time, they roam far over the ocean before returning to their native colony to breed.

Open sea,rocky coasts, offshore islands

HABITAT

ORDER PELECANIFORMES

391

This booby is a superb diver. It is the most widespread booby and has distinct color variations. Most brown boobies are brown all over, apart from a white underside. However, birds from the eastern Pacific have white heads and their bills are gray rather than the typical bright yellow. They all live in the same way, diving for fish and squid from heights of up to 100 ft (30 m). They also skim low over the surface, looking for flying fish, which they catch in midair. They often fly in front of ships, watching for fish caught up in the bow-waves, and they like to fish close to land, roosting on buoys or coastal trees. Despite their agility in the air, they are clumsy at takeoff and landing.

PLUNGE-DIVING Gannets and boobies all show adaptations for a plunge-diving lifestyle: forward-facing eyes, streamlined heads and bills; and nostrils with no external openings. Their wings fold back along the body just before the moment of impact, and the force is absorbed by air sacs under their skin. AERIAL ATTACK

This sequence of photos shows how the wings fold during a dive.

pale, streaked head plumage

DISTRIBUTION Pacific coast of Central America, Galápagos Islands

distinctive blue webbed feet

OCEAN LIFE

This is one of six species of boobies— a group of plunge-diving birds, closely related to gannets, that often have brightly colored feet. The blue-footed booby is brown with white undersides. Its feet are grayish brown in juveniles but brilliant turquoise-blue in adults. Blue-footed boobies often feed in flocks, hitting the water almost simultaneously when they locate a shoal of fish. Smaller than gannets, they are able to fish closer inshore,

392

ANIMAL LIFE ORDER PELECANIFORMES

Guanay Cormorant Phalacrocorax bougainvillii 29–31 in (74–78 cm) LENGTH

WEIGHT 4–5 lb (1.75–2.25 kg)

Desert coasts, islands, inshore waters

HABITAT

DISTRIBUTION

Pacific coast of Peru and northern

Chile

OCEAN LIFE

Boldly marked in black and white, with a conspicuous red patch around each eye, the Guanay cormorant nests in huge colonies along the coast of the

Atacama Desert, the most arid region on Earth. It feeds on anchovetas— small fish that abound in the cold waters of the Humboldt Current. Like other cormorants, it pursues fish underwater, holding its wings against its body and propelling itself with its legs. It floats low down in the water, periodically dipping its head beneath the surface to check for food. Guanay cormorants have nested on the same offshore islands for millennia, depositing deep layers of desiccated droppings known as guano. During El Niño years, when the ocean temperature rises, shortage of food forces these cormorants to forage far afield, often as far north as Panama.

HUMAN IMPACT

THE GUANO TRADE Before the invention of synthetic fertilizers, nitrogen-rich guano was an extremely valuable commodity. Thousands of tons were exported from the South American coast to the Northern Hemisphere. Guano was also used in the manufacture of explosives. GUANO MINING

Using picks and shovels, workers dig up compacted guano on an island off the coast of southern Peru.

BIRDS ORDER PELECANIFORMES

Great Cormorant Phalacrocorax carbo 32–40 in (80–101 cm)

LENGTH

41/4 –51/2 lb (2–2.5 kg)

WEIGHT

Coasts, inshore waters, rivers, lakes

HABITAT

DISTRIBUTION Northeast North America, Europe, Africa, Asia, Australasia

Equally at home in fresh water and at sea, the great cormorant can be found across a vast swath of the world, from Greenland to Australasia. From a distance, its plumage looks jet black, but close up it has a greenish metallic

sheen, with white patches that vary between local races. Like its many relatives, it fishes by pursuit diving and its feathers are only partly waterproof. After feeding, it rests with its wings spread apart to dry. Great cormorants have a strong, direct flight, with steady flapping interspersed with short glides. They can often be seen in small groups, skimming just above the surface of the sea or following rivers inland. They nest on rocky ledges and in trees, making a platform out of seaweed, flotsam, or twigs, and the females lay three or four greenishwhite eggs. Great cormorants are sometimes persecuted by anglers, particularly in trout-fishing regions, but they remain highly successful.

black flight feathers in adult

ORDER FALCONIFORMES

Brahminy Kite Haliastur indus short, wedgeshaped tail

LENGTH 17–20 in (43–51 cm)

14–25 oz (400–700 g)

WEIGHT

Beaches, estuaries, rivers

HABITAT

ORDER FALCONIFORMES

White-bellied Sea Eagle Haliaeetus leucogaster LENGTH 28–35 in (70–90 cm) WEIGHT 51/2 –91/4 lb (2.5–4.2 kg)

Inshore waters, rivers, lakes, reservoirs

HABITAT

DISTRIBUTION South and Southeast Asia, New Guinea, Australia

This black-and-white eagle makes an impressive sight as it soars over water with its wings, up to 6½ ft (2 m) wide, held in a shallow V shape. Its wideranging diet includes fish, water birds, turtles, and sea snakes, which it snatches from the surface, rarely entering the water. It also scavenges and forces smaller sea birds to drop their catch. It breeds close to water, building a large nest in a high tree.

ORDER FALCONIFORMES

Osprey Pandion haliaetus LENGTH 20–26 in (50–65 cm) WEIGHT 23/4 –41/2 lb (1.2–2 kg)

Coasts, reefs, lagoons, rivers, lakes

HABITAT

DISTRIBUTION Worldwide except polar regions, southern South America and New Zealand

This fish-eating hawk has one of the widest distributions of any bird of prey, breeding mainly in the Northern Hemisphere and migrating south for the winter. The Osprey is easy to distinguish from other birds of prey on coasts, thanks to its light build, its

AIRBORNE ATTACK The Osprey cruises high above water looking for food. Once it spots a fish, it hovers for a few seconds before half-folding its wings and going into a steep dive. It hits the water at high speed, sometimes partly sub-merging, before gripping its prey with one foot and climbing laboriously back into the air. Once airborne, it shakes the water off its plumage, before heading to a perching post or to its nest.

DISTRIBUTION South and Southeast Asia, northern Australia, islands of western Pacific

A common scavenger in parts of its range, the Brahminy kite is also an effective hunter, crisscrossing the water from a height of a few yards, dropping to the surface to catch fish, or to pick up scraps of waste. It also feeds on beaches and mudflats, and is seen in the outskirts of coastal towns. Adults have deep chestnut plumage, and a distinctive white chest and head. Their breeding season varies according to location, but they often nest in mangroves, making a platform-shaped nest from seaweed and sticks. Both parents help to raise the one to two young. conspicuous, dark eye-stripe, and its narrow, slightly kinked wings. It feeds entirely on fish, plunging from heights of up to 165 ft (50 m) and entering the water feet-first. Its wings are strong, its legs are heavily muscled, and its toes have long, hooked talons and spiny soles—an adaptation that gives it a firm grip on its slippery prey. These birds have been known to take prey that approaches their own weight. They nest in the tops of high trees and hatch a single brood of two to three chicks each year. During the 20th century, ospreys suffered severely as a result of pesticide pollution, particularly from DDT. Their population has now recovered, and in some regions—for example, northern Britain—they have resumed breeding after a gap of many years.

393

394

ANIMAL LIFE ORDER CHARADRIIFORMES

Snowy Sheathbill Chionis alba 131/2 –16 in (34–41 cm) LENGTH

ORDER CHARADRIIFORMES

Eurasian Oystercatcher Haematopus ostralegus LENGTH 151/2 –19 in (40–48 cm)

1–13/4 lb (450–775 g)

WEIGHT

14–28 oz (400–800 g)

WEIGHT

Rocky coasts, inshore waters, sea ice

HABITAT

Rocky shores, damp inland habitats

HABITAT

DISTRIBUTION Antarctic Peninsula, subantarctic islands, southern South America, Falkland Islands

limpets, and other mollusks, using its bill to smash or pry apart their shells. To locate good feeding sites, it often flies along the tideline, calling loudly to other oystercatchers. On coasts, it nests on shingle and gravel, laying two to four camouflaged eggs. The Eurasian oystercatcher is one of 11 species of oystercatchers (family Haematopodidae). All have the same overall shape and brightly colored bills, but in some species, the plumage is totally black.

Iceland, Europe, N. and E. Asia, (breeding); S. Europe, Africa, S. Asia (non-breeding)

ORDER CHARADRIIFORMES

Black-winged Stilt Himantopus himantopus 14–16 in (35–40 cm)

LENGTH

5–7 oz (150–200 g)

WEIGHT

Shallow coasts, salt marshes, wetlands

HABITAT

Worldwide except far north and northeast Asia; summer visitor only in north of range

DISTRIBUTION

DISTRIBUTION

Sheathbills are the only birds with non-webbed feet that breed on the shores of Antarctica. Stocky and short-legged, they bear a superficial resemblance to chickens, particularly when they escape from danger by running away. Almost wholly carnivorous, they scavenge carrion along the shoreline, and also loiter around penguin colonies to steal eggs and food from adult birds.

With its bright orange bill and loud piping call, this is one of the most conspicuous waders on European shores. Often seen in small parties, it feeds on mussels,

brightly colored bill

The black-winged stilt’s immensely long legs trail far behind its tail when it flies. It has several geographical races and breeds in a broad range of wetland habitats. It feeds in calm fresh or salt water, striding through the shallows, scything its bill through the water to catch small animals or picking them from the surface.

slender, slightly upturned bill

legs longer than body

ORDER CHARADRIIFORMES

Pied Avocet Recurvirostra avosetta LENGTH 161/2 –18 in (42–45 cm) WEIGHT 8–14 oz (225–400 g)

Shallow coasts, salt marshes, wetlands

HABITAT

Europe, temperate Asia (breeding); W. Europe, Africa, S. and S.E. Asia (non-breeding) DISTRIBUTION

OCEAN LIFE

Instantly recognizable by their long upturned bills, avocets are elegant waders that feed in shallow water, both on coasts and inland.There are four species, all similar in shape and size. Of these, the pied avocet is by far the most widespread and is the only species that is found in Europe

and Africa, as well as Asia. Pied avocets feed by dipping their bill in water, and then sweeping it from side to side.The tip of the bill is highly sensitive to touch, so the bird can catch food even in the turbid water of estuaries and lagoons. Pied avocets swim well and sometimes upend to find food in the same way as dabbling ducks.They nest in groups, making cup-shaped hollows on mudflats, where they lay a clutch of four eggs. Despite their dainty appearance,

they can be aggressive if their nests are threatened. Parents charge at intruders with their heads lowered, and they are able to chase away much bulkier birds, such as geese and ducks. ORDER CHARADRIIFORMES

Gray Plover Pluvialis squatarola 10–11 in (26–28 cm)

LENGTH

6–8 oz (170–240 g)

WEIGHT

Arctic tundra, coasts, estuaries

HABITAT

Arctic (breeding); temperate and tropical coasts worldwide (non-breeding)

DISTRIBUTION

This long-distance migrant, one of the most widespread waders, is found on coasts in every continent except Antarctica. In their breeding plumage, seen only in the Arctic tundra, males have a black underside and face, but by the time they head south to winter on coasts, both sexes are a speckled gray. Gray plovers feed on insects in summer and on marine worms and crustaceans in winter.

395 ORDER CHARADRIIFORMES

Ruddy Turnstone Arenaria interpres LENGTH 8½–10 in (21–25 cm) WEIGHT 3–4 oz (80–110 g)

Rocky/sandy coasts, coastal lowlands

HABITAT

DISTRIBUTION Arctic coasts (breeding); temperate and tropical coasts worldwide (non-breeding)

Found on coasts all over the world, the ruddy turnstone feeds in a distinctive way, scuttling along the tideline, flicking stones aside with

ORDER CHARADRIIFORMES

Whimbrel Numenius phaeopus 151/2 –18 in (40–46 cm)

LENGTH

10–16 oz (270–450 g)

WEIGHT

Arctic tundra, coasts, reefs, wetlands

HABITAT

N. Europe, Arctic (breeding); temperate and tropical coasts worldwide (non-breeding) DISTRIBUTION

Using its long, downcurved bill, the whimbrel feeds by probing into wet mud or by extracting animals from rocky crevices. It is one of eight

ORDER CHARADRIIFORMES

Dunlin Calidris alpinus LENGTH 61/2 –81/2 in (16–22 cm)

11/2 –13/4 oz (40–50 g)

WEIGHT

Coasts, marshes, tundra

HABITAT

DISTRIBUTION Arctic, subarctic (breeding); temperate and tropical coasts in N. hemisphere (non-breeding)

similar species, collectively known as curlews, that have mottled brown plumage, sharply pointed wings, and bills up to 8 in (20 cm) long. The whimbrel’s bill is only half this length, but it is a precision instrument, with sensitive nerve-endings at its tip that enable the bird to feel for buried food. The whimbrel is strongly migratory, nesting inland across much of the far north, in marshy open country. At this time of the year, the male sings from high in the air, gradually descending on widely spread wings. After breeding, whimbrels head south along coastlines, reaching as far south as the tip of South America and New Zealand.

ORDER CHARADRIIFORMES

Gray Phalarope Phalaropus fulicarius LENGTH 8–9 in (20–22 cm) WEIGHT

2–3 oz (50–75 g)

Marshy coastal tundra, plankton-rich open ocean

HABITAT

a deft movement of its bill. This often reveals sandhoppers and other small animals, which it snaps up or chases. Ruddy turnstones, like many waders, nest in the far north, but their feeding habits restrict them to coastal areas. After breeding, their southward migration takes them to coasts on every continent except Antarctica. plumage than the male. Once she has mated and laid her eggs, she takes no part in incubation or raising the young. By comparison with other waders, gray phalaropes are highly aquatic birds and spend much of their time afloat. They breed close to coasts, and once they have migrated south, they often overwinter far out at sea.

DISTRIBUTION Arctic coasts (breeding); South Atlantic and eastern South Pacific (non-breeding)

Also known as the red phalarope, this short-billed wader shows a remarkable reversal of roles when it breeds. Unlike most birds, the female—shown here—has a much brighter breeding in a range of habitats from moorland to tundra, often some distance inland. Both parents help to incubate the eggs and raise the young. After breeding, they gather in flocks to migrate to warmer coasts, but rarely travel into the Southern Hemisphere. Other members of this genus include many other flock-forming species, such as the red knot and sanderling, most of which travel as far north as the Arctic Ocean to breed.

WINTER FLOCKS Wintering waders form some of the largest bird flocks to be found on coasts. Flocking makes it harder for predators to approach unseen and helps young birds to locate good feeding sites by following adults. Some waders, such as the purple sandpiper and ruddy turnstone, frequently form mixed flocks. AERIAL MANEUVERS

In winter, flocks of dunlins create a breathtaking spectacle, as they wheel in the thousands over coastal feeding grounds. Up close, the dunlin is a typical calidrid wader, one of over two dozen similar species that feed on coasts worldwide. It has a compact body, narrow wings, a tapering tail, and a black, finely pointed bill. Its plumage is variable, but breeding

Flocks of overwintering dunlins show extraordinary coordination, with thousands of birds changing direction almost simultaneously.

males usually have a black patch on the underside, which fades when they molt. Dunlins mainly eat small crustaceans and mollusks that live just beneath the surface of the shore. When feeding, they usually stay close

to the water’s edge, alternately pecking into the mud or sand, and then running forward at high speed. Dunlins breed in the Arctic and subarctic, where they nest

OCEAN LIFE

396

ANIMAL LIFE ORDER CHARADRIIFORMES

Swallow-tailed Gull Creagrus furcatus LENGTH 211/2 –231/2 in (55–60 cm) WEIGHT 21–32 oz (600–900 g)

Coasts, inshore waters, open sea

HABITAT

DISTRIBUTION Galápagos Islands and Malpelo Island (breeding); Pacific coast of South America

Distinguished by its sharply forked tail, this South American gull is atypical in feeding at night. It eats squid and fish, spotting them with its large eyes, which are surrounded by distinctive red rings and angled forward to give a wide field of binocular vision. Swallow-tailed gulls nest on islands and disperse far out to sea during the rest of the year.

ORDER CHARADRIIFORMES

Great Black-backed Gull Larus marinus LENGTH 28–31 in (71–79 cm) WEIGHT 23/4 –43/4 lb (1.2–2.1 kg)

SCAVENGING

Rocky coasts, islands, inland in winter

HABITAT

DISTRIBUTION

Scavenged food forms a large part of the herring gull’s diet, both on land and at sea. This gull has benefited from urban expansion and the growth in fishing, both of which generate a large supply of edible waste. Herring gulls may cause problems at inland garbage dumps by picking up waste and carrying it away.

North Atlantic, breeding north

to Svalbard

With a wingspan of up to 51/2 ft (1.7 m), the great black-backed is one of the world’s largest gulls. Heavily built, with black upperwings and a powerful bill, it scavenges food, but it is also a highly predatory bird. It frequently preys on other sea birds and their young, and will attack mammals as large as rabbits. It breeds alone or in colonies, nesting on cliff ledges or on open ground.

ORDER CHARADRIIFORMES

Herring Gull Larus argentatus 22–26 in (56–66 cm)

LENGTH

OCEAN LIFE

WEIGHT 13/4 –23/4 lb (750 g–1.25 kg)

Coasts, reservoirs, urban areas

HABITAT

DISTRIBUTION

Worldwide in Northern Hemisphere

Noisy, assertive, and always on the lookout for a meal, this is the most widespread gull in the Northern Hemisphere. It has gray upperparts and black wingtips, and a large yellow bill with a conspicuous red spot near the

tip.Young herring gulls are mottled brown, and it takes them three years to develop the full adult plumage. Often seen in flocks, herring gulls are highly adaptable birds, feeding on anything edible that they can find. They rarely venture far out to sea, but their range extends a long way inland, where they are often associated with humans—following tractors to eat earthworms turned up by the plow, or wheeling noisily over garbage dumps. Herring gulls nest on the ground and on rooftops, typically laying three eggs. They can be highly aggressive if their nests are disturbed.

FOOD OVERBOARD

Large numbers of herring gulls follow fishing ships operating close to coasts. Unlike pelagic birds, they usually return to land at night.

BIRDS ORDER CHARADRIIFORMES

Black-legged Kittiwake Rissa tridactyla LENGTH 151/2 –18 in (39–46 cm) WEIGHT 11–18 oz (300–500 g)

Rocky coasts, inshore waters, open sea

HABITAT

DISTRIBUTION Northern hemisphere; breeds north to Svalbard and Greenland

ORDER CHARADRIIFORMES

Laughing Gull Larus atricilla 15–17 in (38–43 cm)

LENGTH

11–18 oz (300–500 g)

WEIGHT

HABITAT

Coasts, inshore

waters DISTRIBUTION North America, Caribbean, Central America (breeding); N. South America (non-breeding)

ORDER CHARADRIIFORMES

Ivory Gull Pagophila eburnea 16–18 in (40–46 cm)

LENGTH

1–11/4 lb (450–600 g)

WEIGHT

Coasts, open sea, sea ice

HABITAT

DISTRIBUTION Arctic Ocean, north Atlantic, wintering in south of range

A widespread summer visitor to North American coasts, the laughing gull rarely wanders far inland. It feeds mainly by scavenging and often follows ferries and fishing boats. Bold and self-confident, it is a familiar sight to picnickers on beaches, where it pushes larger gulls aside in the competition to get at food. It nests in large colonies on coasts. Like many dark-headed gulls, it loses its black cap during the non-breeding season, when its head turns a dull white. Completely white, apart from its yellow-tipped bill, black eyes, and black feet, the ivory gull is the world’s most northerly breeding bird. With its buoyant flight and pigeonlike walk, it ranges across open water and sea ice, and it can be found almost anywhere over the Arctic Ocean. It feeds largely by scavenging and is quickly attracted to the carcasses of dead seals and whales. The ivory gull is currently undergoing a steep decline. The reasons for this are unclear.

have longer claws than those of most other gulls, and they build cup-shaped nests out of seaweed and mud, which help to keep their eggs secure. Both parents help to incubate the eggs and feed the young, and the adults’ recognition calls can make a deafening noise when several hundred pairs nest close together. After breeding, these birds disperse away from the coast, traveling as far south as tropics off West Africa. They are monogamous, with pairs meeting up again at the same nesting site after spending up to eight months apart.

Kittiwakes get their name from their call—a loud, three-syllable shriek that echoes around their nesting colonies on northern coasts. A medium-sized, gray-backed gull, the black-legged kittiwake breeds on narrow cliff ledges but spends the rest of the year wandering far out to sea. It feeds mainly on small fish, and often follows fishing vessels. Unlike most gulls, however, it rarely shows any interest in scavenging food on land. Black-legged kittiwakes have evolved several adaptations for breeding on bare rock. Their feet

ORDER CHARADRIIFORMES

Brown Noddy Anous stolidus LENGTH 16–18 in (40–45 cm) WEIGHT 7–9 oz (200–250 g)

Open sea, inshore, oceanic islands

HABITAT

DISTRIBUTION Worldwide in tropical waters; present on some islands year-round

Noddies are dark, tropical terns that often feed far out to sea. There are three species of noddies and the brown noddy is the largest and most widespread. Brownish black all over, apart from a paler crown, it has slender wings, a long, sharp bill, and small, jet-black legs. Brown noddies feed mainly on fish and squid, hovering and then plunging in the same way as terns. They nest on islands throughout the tropics, making nests from twigs and seaweed in trees or on the ground.

ORDER CHARADRIIFORMES

ORDER CHARADRIIFORMES

Caspian Tern

Inca Tern

Sterna caspia

Larosterna inca LENGTH

19–23 in (48–59 cm)

LENGTH

WEIGHT

11/4 –13/4 lb (550–750 g)

WEIGHT

16–17 in (40–42 cm)

Coasts, lakes, reservoirs, gravel pits

HABITAT

6–8 oz (175–225 g)

Coasts and inshore waters

HABITAT

DISTRIBUTION Pacific coast of South America from Ecuador to central Chile

DISTRIBUTION North America, Eurasia, Africa, Australia (breeding); northern South America, Southeast Asia (non-breeding)

ORDER CHARADRIIFORMES

White Tern Gygis alba LENGTH 11–13 in (28–33 cm) WEIGHT 31/2 –41/2 oz (100–125 g) HABITAT Open sea, inshore, oceanic islands DISTRIBUTION

Tropical waters worldwide

Also known as the fairy tern, this delicate and graceful bird wanders far out over tropical oceans, where it is known for its habit of fluttering close to boats. Slim and lightly built, with

black eyes and a straight black bill, it is the only tern whose plumage is entirely white. It spends most of its time flying a few yards above the surface, periodically dropping down in order to catch small fish and squid. Unlike most terns, it is a solitary breeder, nesting on widely scattered islands. It lays its single egg on a rocky ledge, or in a slight hollow in a sloping branch. The parents take turns cradling the egg throughout its five-week incubation period—an unusually long time for an egg of its size. The chick emerges with strong feet and claws for clinging to its nesting site.

With its curling white “mustache” plumes, this South American tern is easy to identify. It feeds in the cold, nutrient-rich waters of the Humboldt Current, dipping down to the surface to catch small fish. Inca terns often follow sea lions and whales, preying on shoals of fish as they try to escape the larger predators. They nest among rocks or in abandoned burrows.

OCEAN LIFE

Despite its name, this large, blackcrested tern has a global distribution. Gray-backed, with a large, dark red bill, it has a black cap that is darkest when it breeds. It plunge-dives for food in shallow water, and nests in colonies, laying its eggs directly on gravel or mud.

397

398

ANIMAL LIFE ORDER CHARADRIIFORMES

ORDER CHARADRIIFORMES

Black Skimmer

Arctic Skua

Rynchops niger

Stercorarius parasiticus LENGTH

16–20 in (40–50 cm)

LENGTH

WEIGHT 9–14 oz (250–400 g)

WEIGHT

Estuaries, lagoons, lakes, coasts

HABITAT

18–26 in (46–65 cm)

14–21 oz (400–600 g)

Coasts, tundra, moorland, open sea

HABITAT

DISTRIBUTION Pacific and Atlantic coasts of North, Central, and South America, north to Massachusetts

Similar to terns in overall shape, skimmers have remarkable and highly distinctive bills. The lower part, or mandible, of the bill is at least a third longer than the upper part and is laterally compressed, giving it a shape like a scissor blade. When feeding, a skimmer flies low over calm water with its lower mandible slicing through the surface. If the mandible

touches food, the skimmer snaps its bill shut, flicking its catch into its mouth. The black skimmer is one of three species of skimmers, all of which are dark above, with white underparts. Like its relatives, it often feeds at dawn and dusk, and it will also feed during the night if the moonlight is bright enough. It lives in small flocks and nests on beaches and sand spits, laying its eggs in an unlined hollow on the ground. It is migratory in the far north and south of its range.

ORDER CHARADRIIFORMES

Great Skua Stercorarius skua LENGTH 20–26 in (51–66 cm) WEIGHT 23/4 –31/2 lb (1.2–1.6 kg)

Coasts, inshore waters, open sea

HABITAT

DISTRIBUTION North Atlantic (breeding), dispersing south to equator (non-breeding)

Powerfully built, with short, broad wings, the great skua is shaped like an unusually thickset gull, but it has mottled, dark brown plumage that changes only slightly as it matures. It is a rapacious predator, eating fish, small mammals, and also other birds, as well as raiding nests for eggs and chicks. Normally slow and ponderous in the air, it becomes swift and agile when it hunts, and chases birds as large as gannets to force them to regurgitate their food, which it then eats. The great skua nests on the ground and spends the rest of the year at sea.

ORDER CHARADRIIFORMES

Common Murre Uria aalge LENGTH 151/2 –161/2 in (39–42 cm) WEIGHT 13/4 –21/2 lb (850 g–1.1 kg)

Inshore waters, rocky coasts, open sea

HABITAT

OCEAN LIFE

DISTRIBUTION

North Atlantic, north Pacific

Conspicuously marked in brownish black and gleaming white, the common murre spends most of the year at sea. It dives for fish from the surface, swimming underwater using its wings. In spring, common murres crowd together on narrow cliff ledges, where each female lays a single egg directly on to the rock. When the chick is fully grown, the male parent escorts it into the sea.

ADAPTED EGGS Murre eggs are distinctly pointed at one end and will roll around in a circle if disturbed. This adaptation keeps them from falling off the narrow cliff ledges where they are laid. Their color varies greatly and their irregular surface markings of dark blotches and intricate scribbling may aid identification by the parents. markings unique to each egg

Northern waters (breeding); throughout Southern Hemisphere (non-breeding)

DISTRIBUTION

This slender-winged sea bird, also called the parasitic or Arctic jaeger, is exceptionally fast and maneuverable in the air—a skill that is central to the

way it feeds.There are several color forms, which differ in their proportion of brown and gray, but all have streamers that give their tails a sharp central point. This species catches fish, but it is better known as a kleptoparasite, which steals food from other birds. It swoops down on gulls and terns as they return from the sea, chasing them and often gripping their tail feathers with its bill. Its victims react by disgorging food, which the skua deftly intercepts in midair. Arctic skuas also hunt small land animals and steal eggs and chicks from nests.They nest on the ground and winter at sea.

399 ORDER CHARADRIIFORMES

Atlantic Puffin Fratercula arctica 11–12 in (28–30 cm)

LENGTH

WEIGHT

14 oz (400 g)

Inshore waters, rocky coasts, open sea

HABITAT

North Atlantic, breeding north to Greenland and Svalbard

DISTRIBUTION

HUMAN IMPACT

With its vividly marked bill, bright red feet, and red-and-black eye patches, this is the most colorful sea bird in the north Atlantic. Like other members of the auk family, it feeds by pursuing fish underwater, using its strong, stubby wings to swim. In the air, it flies rapidly on fast-beating wings, skimming over the waves as it returns to its nest with food. Atlantic puffins breed in large clifftop colonies, digging burrows in coastal turf. The parents take turns incubating the single egg, and they both help to feed the developing nestling. Instead of

ORDER CHARADRIIFORMES

Least Auklet Aethia pusilla LENGTH

6 in (15 cm)

WEIGHT

3 oz (85 g)

Inshore waters, rocky coasts, open sea

HABITAT

DISTRIBUTION North Pacific, breeding mainly in the Aleutian Islands and islands in Bering Sea

regurgitating food, as most sea birds do, they return with small fish held in their bills, carrying about six fish simultaneously, arranged alternately head to tail. Each nestling is fed continuously for about six weeks, after which the parents abandon it and head out to sea. After going without food for several days, the young bird crawls out of the burrow and flutters down to the sea after dark. Puffins disperse out to sea in fall, when they lose the bright bill colors that make them so conspicuous during the summer months. This tiny bird is probably the most abundant species of auk, a family that also includes murres and puffins. Short, plump, and gray-backed, with a stubby red-tipped bill, it nests in vast colonies off the Alaskan coast, some of which contain more than a million birds. Least auklets also feed together, floating on the surface in large gatherings known as “rafts.” They are pursuit divers that eat mainly zooplankton.

Crested Auklet Aethia cristatella LENGTH 91/2–101/2 in (24–27 cm)

9 oz (250 g)

Inshore waters, rocky coasts, open sea

HABITAT

DISTRIBUTION North Pacific, breeding mainly in the Aleutian Islands and islands in Bering Sea

UNFAIR SHARES

A catch of sand eels is brought aboard a boat. These finger-shaped fish, unrelated to true eels, are an important food for some fish and sea birds.

ORDER CORACIIFORMES

Pied Kingfisher Ceryle rudis LENGTH

10 in (25 cm)

WEIGHT

31/4 oz (90 g)

single band. Pairs nest in burrows in sandy banks and are often helped by the previous year’s young to collect food for the nestlings. The adults have a loud, high-pitched call, which may be heard as they speed past.

Coasts, lagoons, estuaries, rivers, marshes

HABITAT

DISTRIBUTION

Africa, Middle East, south Asia

ORDER CORACIIFORMES

Collared Kingfisher Todirhamphus chloris

courtship displays are energetic and noisy, as they throw back their heads and make loud grunts and trumpeting sounds. When the breeding season is over, they disperse out to sea and spend the winter as far south as Japan.

LENGTH

11 in (28 cm)

WEIGHT

41/2 oz (120 g)

Forests, coasts, beaches, mangrove swamps, estuaries

HABITAT

DISTRIBUTION Red Sea, Persian Gulf, Southeast Asia, Australasia

Also known as the mangrove kingfisher, this bird lives in a variety of habitats, although in Australia it is restricted to the coast. Greenish blue above, with a white belly and collar, it has a black eye-stripe and a sharply pointed bill. On coasts, it hunts crabs as well as fish and, like all kingfishers except the pied (see above), beats its prey against a perch before swallowing it. It often nests in hollows in mangrove trees, and lays three or four eggs. In the far south of its range, this bird is a summer visitor only.

OCEAN LIFE

The north Pacific is home to more species of auks than anywhere else. The crested auklet is a typical example, with a compact body, sooty-gray plumage, and a feathery crest that curves forward from its forehead over its orange-red bill. Like other auks, it flies low on rapidly whirring wings and feeds in flocks so dense that they resemble swarms of insects wheeling over the water. Crested auklets breed among fallen rocks on island coasts, in colonies containing thousands of birds. Their

The puffin population has fallen sharply of late, especially in the eastern Atlantic. This may be due to the growing fishery for sand eels, a fish that puffins rely on, especially in breeding season. Sand eels are used in fertilizers, animal foods, and as a source of edible oil.

This boldly patterned, black-andwhite bird is the only kingfisher that regularly fishes offshore. Instead of watching for prey from a perch, as many other kingfisher species do, it flies rapidly above the surface with its head facing down as it scans the water below. If it spots food, it hovers on the spot, and then dives down to make a catch. It can also eat while in flight, another unique adaptation. Male and female pied kingfishers look similar, although the female has a double breast band compared to the male’s

ORDER CHARADRIIFORMES

WEIGHT

COMPETING FOR FOOD

400

ANIMAL LIFE

Mammals DOMAIN Eucarya KINGDOM Animalia PHYLUM Chordata CLASS Mammalia ORDERS 27 SPECIES About 5,500

ONLY A SMALL MINORITY OF THE WORLD’S

mammals live in seawater, but taken together, they show an extraordinary range of shapes, sizes, and lifestyles. They include cetaceans (whales and dolphins), sirenians (manatees and dugongs), and carnivores, particularly the pinniped carnivores (seals, sea lions, and walruses). All marine mammals breathe air, like their terrestrial counterparts, and they give birth to live young, either in the sea or onshore. Many species are migratory, with a sophisticated navigational sense. heart beats rapidly after surfacing

Anatomy and Physiology 180 160 HEART RATE (BPM)

DIVING MAMMAL Marine mammals have many adaptations for life at sea, When a Harbour Seal not only in their anatomy, but also in their physiology, dives, its heart rate regulating how their bodies work. Cetaceans and falls below 10 beats a sirenians have lost all visible traces of hind limbs; instead, minute. Blood diverted they propel themselves with their tail flippers or flukes, from its muscles and digestive system flows which beat up and down. Fur seals and sea lions swim to its heart and brain. with their front flippers, while true seals use their rear flippers, bringing them together like a pair of hands. Despite needing to breathe air, many marine mammals are superb divers. Some, such as the elephant seal, can reach depths of over 3,300 ft (1,000 m) and stay underwater for up to two hours.When they dive, their heart rate drops, and blood flow is modified so that vital organs receive enough oxygen until they resurface. Instead of breathing in before they dive, the deepest divers often exhale. This helps them to avoid decompression sickness, or the “bends.”

140 heart rate drops as seal dives

120 100 80 60

rate remains low throughout dive

40 20 0

2

4

6

TIME (minutes)

humerus

radius

phalange

SHARED PATTERNS

A sea lion’s front flipper has the same arrangement of bones as a human arm. The “arm” bones are short and sturdy, helping to bear the animal’s bulk on land. Long finger bones make up the flipper’s blade.

ulna

blowhole

INSULATING BLUBBER FLIPPERS AND FLUKES

A humpback whale’s flippers contain bones, and beat like a pair of wings. Its flukes, or tail fins, are made of rubbery tissue, and contain no bones at all.

Compared to air, seawater drains much more heat from mammals’ bodies. To keep warm, many polar species, such as this walrus, have a thick layer of ear drum insulating fat, called blubber, under the skin. sound channel in jaw

VARIED DIET

OCEAN LIFE

Penguins are just one item on the leopard seal’s menu. Despite its reputation for ferocity, at least half of its diet consists of krill, which it filters with its cheek teeth.

scapula

metacarpal sonic lips (source of sound) outgoing clicks (to prey)

melon incoming (reflected) clicks

USING ECHOLOCATION

Dolphins and toothed whales use pulses of high-pitched sound to locate prey. The forehead contains an oil-filled organ called the melon, which is thought to function as an “acoustic lens” to focus outgoing sound.

Feeding Apart from plant-eating manatees and dugongs, most marine mammals are exclusively carnivorous. In open water, many pursue individual prey, tracking it by sight or by echolocation. Some seals have a twin strategy. They catch prey individually, but they can also filter out planktonic animals in bulk, using complex cheek teeth that interlock to form a sieve. This efficient feeding method reaches extremes in the baleen whales, which cruise through shoals of fish or krill, often swallowing over 220 lb (100 kg) of food at a time. Not all marine mammals catch moving prey. Sea otters dive to collect clams, mussels, and sea urchins, while walruses and gray whales suck mollusks out of seabed sediment.

MAMMALS

401

Breeding Marine mammals typically produce a single young each time they breed. Cetaceans and sirenians give birth in water, as do sea otters, but all other marine mammals have to return to land. In species with a harem system, such as fur seals and elephant seals, fighting between rival males for control of mates can be ferocious. After mating, the females of most marine mammals raise their young on their own. For their size, true seals develop fastest, some being weaned in as little as five days. At the other end of the spectrum, a dolphin calf may suckle for over 20 months—the start of a mother-calf bond that can last for six years. SEA OTTER PUP

A young sea otter rides on its mother’s chest, while she floats in calm water. The pup depends on her for at least five months.

HUMAN IMPACT

THREATS AND CONSERVATION Historically, marine mammals have been heavily exploited for their food, oil, and fur, bringing some species close to extinction. Whales and seals are the primary targets. In 1986, the International Whaling Commission agreed on a moratorium on all commercial whaling. Despite dissent, this ban remains in force. Seals continue to be hunted, or culled, to control populations, but the rarest species are protected by international agreements.

COLONY BREEDING

ENGRAVED WHALE TOOTH

Many seals and sea lions, such as these South American sea lions, are highly sociable in the breeding season, forming large colonies on beaches to mate and have their pups.

The art of scrimshaw, or engraving on whale teeth and walrus tusks, was popular among whalers during the 17th and 18th centuries. Whalebone carving still takes place in areas where small-scale native whaling is permitted.

MARINE MAMMAL CLASSIFICATION Two orders of mammals—the cetaceans and sirenians—are wholly marine. Seals and sea lions are also aquatic, but like other members of the carnivore order, they give birth on land. Several other carnivore species feed at sea, but of these only the sea otter is entirely marine. CARNIVORES Order Carnivora Most carnivores are terrestrial, but a few spend some of their lives in the sea. The polar bear is equally at home on dry land, on sea ice, and in salt water. Seven species of otter often enter salt water, but the sea otter is the only one to spend all of its time offshore. The most fully aquatic carnivores

85 species

Cetaceans are divided into two suborders. The 13 baleen whales lack teeth, and filter food from the water using a fibrous material called baleen. The 72 toothed whales are predators that hunt individual prey. Cetaceans give birth at sea, and are helpless if stranded on land. SIRENIANS Order Sirenia 4 species

Living mainly in the tropics, sirenians, or sea cows, are barrel-shaped vegetarians that live

in salt and fresh water. They include the dugong and three species of manatees, such as the Caribbean manatee, below. Slowmoving and thick-skinned, sirenians have broad muzzles, paddlelike front flippers, and a broad, horizontally flattened tail.

OCEAN LIFE

249 species

are the 34 species of pinnipeds, until recently classified in their own order, the Pinnipedia. They are split into three families. One family comprises the sea lions and fur seals, which have external ears, use their forelimbs for propulsion, and use all four flippers to move on land. The second family is composed of the true seals, which lack external ears, use hind limbs for propulsion and are less mobile on land. The final family contains only the walrus, which has very wrinkled skin and long tusks.

CETACEANS Order Cetacea

402

ANIMAL LIFE

ORDER CARNIVORA

Polar Bear Ursus maritimus LENGTH

Up to 8 ft (2.5 m)

Females up to 650 lb (300 kg); males up to 1,750 lb (800 kg)

WEIGHT

thick fur over layer of blubber for insulation

Arctic tundra, pack ice, open sea

HABITAT

Circumpolar in the Arctic, southward as far as Newfoundland and the Pribilof Islands

DISTRIBUTION

large paws, furred on both sides

ORDER CARNIVORA

SLEEPING SECURELY

Sea Otter Enhydra lutris LENGTH

21/4 –51/4 ft

(0.7–1.6 m) including tail WEIGHT 33–100 lb (15–45 kg) HABITAT Inshore waters along rocky coasts DISTRIBUTION

North Pacific from Japan to Alaska

and California

Unlike other otters, the sea otter is able to spend its whole life in the ocean. It has a blunt head, a stocky body, webbed rear feet, and small front paws with sharp claws. It uses these to gather food and pick up large stones. At the surface, it floats on its back, using a stone that rests on its chest as an anvil to smash open its prey. Sea otters feed on mollusks, sea urchins, and crabs.While they can dive to 130 ft (40 m), they rarely venture more than 1/2 mile (1 km) from the shore.

Sea otters often sleep in beds of giant kelp, using the seaweed to keep from drifting away. Their fur is the densest of any mammal. The hairs are packed so tightly that they prevent water penetration, ensuring that the otter’s skin never gets wet. This is a vital adaptation, because sea otters live in cold water and do not have insulating fat.

Icon of the Arctic, the polar bear is the largest mammalian carnivore and has incomparable stamina, resilience, and power. Its body is streamlined, the head grading almost imperceptibly

ORDER CARNIVORA

Marine Otter Lontra felina Up to 3 ft (95 cm) including tail

LENGTH

WEIGHT

9–13 lb

(4–6 kg) HABITAT

Exposed rocky

shores Pacific coast of South America from Peru to Cape Horn

DISTRIBUTION

This lithe predator lives on some of the world’s stormiest coastlines, particularly in the remote southern part of its range. The marine otter’s closest relatives live

ORDER CARNIVORA

European Otter Lutra lutra LENGTH 3–31/2 ft (90–110 cm) including tail

15–22 lb (7–10 kg)

WEIGHT

Rivers, lakes, estuaries, rocky coasts

HABITAT

Temperate and tropical Eurasia, south to Indonesia

OCEAN LIFE

DISTRIBUTION

into a long, powerful neck. Its huge paws may be over 12 in (30 cm) wide and are furred on their undersides, providing grip while retaining body heat. Its hearing and sense of smell are acute: it can hear prey that is under 3 ft (1 m) or more of ice and can smell carrion 3 miles (5 km) away. Polar bears spend most of the year at sea, roaming the drifting pack ice and swimming across open areas. Naturally buoyant, they can swim for hours, although they hunt mainly on the ice. The main prey of polar bears is seals, often caught at breathing holes. They also eat sea birds and fish, and the corpses of beached whales are a favorite food. During the summer, many of them live on land and eat a wider range of food, from reindeer to berries. Females give birth in winter, suckling their cubs in a den dug in the snow. For centuries, the polar bear has been hunted by native peoples of the Arctic, without its numbers declining. However, thinning of the Arctic’s sea-ice by global warming could seriously reduce its access to food. mainly in fresh water, but it spends almost all its time in the sea. Like typical river otters, this coast-dwelling otter has short brownish yellow fur, webbed toes on all four feet, and sensitive whiskers that help it to find prey. It fishes along rocky coasts, in the rich waters of the Humboldt Current, and instead of making burrows, it shelters in sea caves just above the level of the highest tides. Marine otters have long been hunted for their pelts, and current estimates of the population are as low as 1,000 animals.The species is now protected, but preservation of its habitat may be equally important in guaranteeing its long-term survival. Once widespread throughout Europe and Asia, the European otter has been badly affected by pollution and habitat change and by being hunted for its fur. It has a streamlined body, short but dense coat, and webbing on all four paws, and is extraordinarily agile underwater, twisting and turning to catch fish. Inland, European otters are largely nocturnal, spending the daytime in their dens, or holts. Those that live on the coast, however, can often be seen during the day.

MAMMALS ORDER CARNIVORA

ORDER CARNIVORA

Antarctic Fur Seal

Northern Fur Seal

Arctocephalus gazella

Callorhinus ursinus

LENGTH

5–61/2 ft (1.5–2 m)

LENGTH 41/2 –7 ft (1.4–2.1 m)

WEIGHT

110–350 lb (50–160 kg)

WEIGHT 110–600 lb (50–270 kg)

Rocky coasts, open sea in polar waters

HABITAT Coasts and sea in cold-water regions

HABITAT

DISTRIBUTION

Southern Ocean

DISTRIBUTION

North Pacific, Bering Sea

Of the nine species of fur seals, most live in the Southern Hemisphere; this is the only northern species that exists in significant numbers. Like other fur seals, it has a thick, dark coat, external ears, and long front flippers that it uses for swimming and for moving around on land. Males can be five times heavier than females, but both sexes have short muzzles, giving them a characteristic

403

snub-nosed look. Their large eyes allow them to see at night, which is when they do most of their feeding, as their prey is closer to the surface. They feed mainly on fish, but also on squid and sea birds, and migrate far out into the Pacific after they breed. Most northern fur seals breed on islands in the Bering Sea. Decimated by commercial hunters from the mid-1700s onward, they are now protected by hunting controls.

Ranging further south than any other fur seal, this polar species feeds on fish, squid, and krill in the icy waters off Antarctica. In spring it comes ashore after spending winter at sea. Males are up to three times heavier than females, with an imposing mane and thickened neck that gives them a front-heavy appearance. This species breeds on islands, such as South Georgia and Kerguelen, and is rising in number. This may be a side effect of the whaling industry, which has reduced competition for krill.

ORDER CARNIVORA

South American Fur Seal

ORDER CARNIVORA

California Sea Lion Zalophus californianus

Arctocephalus australis

LENGTH 61/2 –81/4 ft (2–2.5 m)

41/2 –61/4 ft (1.4–1.9 m)

LENGTH

WEIGHT 240–880 lb (110–400 kg)

130–440 lb (60–200 kg)

WEIGHT

Coasts and sea in cold-water regions

HABITAT

DISTRIBUTION Pacific and Atlantic coasts of southern South America, Falkland Islands

Once found along the entire length of South America’s southern coasts, this fur seal now breeds on offshore islands, where it faces less disturbance from humans. It is blackish gray, with paler undersides in females, and is agile on land, using its flippers to climb steep rocks. Males may be about three times the weight of females. This species feeds mainly at night, hunting fish, squid, lobsters, and crabs, and is itself hunted by sharks and killer whales.

HABITAT Rocky coasts and open sea DISTRIBUTION

Pacific coast of the US

Famed for its acrobatic antics in marine aquariums, the California sea lion is just as agile in the wild. Its sleek body is covered with short fur, which ranges in color from brownish black in males to light brown in females and young; mature males may be more than three times as heavy as females and have a distinctive bony hump on their heads. They feed on fish and squid.

ORDER CARNIVORA

Walrus Odobenus rosmarus 101/4–111/2 ft (3.1–3.5 m)

LENGTH

WEIGHT 2,750–3,750 lb (1,250–1,700 kg)

Coasts and shallow open water

HABITAT

DISTRIBUTION

Arctic Ocean, Bering Sea, Hudson Bay

OCEAN LIFE

Instantly recognizable by its tusks, the walrus is the second-largest pinniped after the elephant seals. Its skin is unlike any other mammal’s, with deep creases and wrinkles, but very little hair. Its color varies enormously: young walruses can be very dark, while old individuals are sometimes a mottled pink. Beneath the skin is a thick layer of fat, or blubber, which keeps their bodies warm. Walruses feed

on shellfish, which they find in the seabed sediment at depths of up to 165 ft (50 m). They locate their food mainly by touch, using stiff whiskers that resemble a mustache. At one time, it was thought that they used their tusks to dredge up their food, but it is now known that they uncover it by squirting water with their mouths. Once their prey has been uncovered, they separate the soft parts from the shells. It is unclear how they do this, but their feeding technique probably involves suction rather than crushing, because intact shells are often found around their breathing holes. Females give birth to a single calf after a 15-month gestation, and they breed only every other year. Walruses are highly gregarious, making them easy prey for hunters. They have been hunted by indigenous peoples for at least 15,000 years, both for food and for their hides.

AUSTRALIAN SEA LIONS

Foraging in the cold waters of the Great Australian Bight, Australian sea lions feed on squid and octopuses as well as fish. Like other sea lions, they use their front flippers to swim. On land, their rear flippers swivel forward, allowing them to move on all fours as fast as a human can run.

406

ANIMAL LIFE ORDER CARNIVORA

Common Seal Phoca vitulina 43/5–61/4 ft (1.4–1.9 m)

LENGTH

WEIGHT 120–375 lb (55–170 kg)

Inshore waters, estuaries, rivers

HABITAT

DISTRIBUTION North Pacific and north Atlantic, reaching as far south as Baja California

Also known as the harbor seal, this species has the widest distribution of any seal and the widest variety of markings. Its background color ranges from pale gray to brown, with dark spots and rings and sometimes a dark stripe along the back. It has a smoothly domed head and a doglike muzzle. It feeds primarily on fish, often catching them in shallow water close to the shore. It dives

for up to five minutes, but rarely to any great depth. The common seal spends much of its time on rock flats and sandbanks, and it is here that the females give birth. The pups shed their soft natal coat before they are born, starting life with a dark version of the adult coat, unlike the pups of some other seals. Although they can swim almost immediately, they often use their front flippers to ride on their mother’s back. They are weaned at about four weeks. True to their name, common seals are still abundant, but in the North Sea they have been adversely affected by pollution, and also by a highly infectious viral disease that broke out in the late 1980s.

ORDER CARNIVORA

Ringed Seal Pusa hispida 41/4–5 ft (1.3–1.5 m)

LENGTH

100–210 lb (45–95 kg)

WEIGHT

Polar waters around sea ice

HABITAT

Arctic Ocean, north Pacific, north Atlantic, Baltic Sea, Sea of Okhotsk

DISTRIBUTION

Named after its conspicuous circular markings, the ringed seal is found throughout the Arctic, in open water near sea ice and also under the ice

ORDER CARNIVORA

Gray Seal Halichoerus grypus 6–71/2 ft (1.8–2.3 m)

LENGTH

550–880 lb (250–400 kg)

WEIGHT

Rocky coasts, offshore islands

HABITAT

Discontinuous populations in northwest Atlantic, Iceland, British Isles, Baltic Sea

DISTRIBUTION

clawed front flipper

ORDER CARNIVORA

Harp Seal Pagophilus groenlandicus 51/2–61/4 ft (1.7–1.9 m)

LENGTH

WEIGHT 265–310 lb (120–140 kg) HABITAT

Polar waters

DISTRIBUTION North Atlantic and adjoining regions of the Arctic Ocean, extending eastward to Siberia

One of the most common seals in the far north, the harp seal is born with an exceptionally luxurious coat of long white fur, which camouflages the pups as they lie on sea ice. Adult harp seals are silvery-gray with a mottled pattern

of dark patches, which become more prominent as they age. They feed mainly on fish and shrimp, living on the southern edge of the Arctic pack ice, and resting on it when they molt. In early spring, adult females give birth to a single pup each, which they wean after just 12 days. At this point, the pup gradually sheds its white coat and takes up life in the sea. For many decades, the pups have been the subject of a controversial hunt, which supplies their pelts to the fur trade. Despite campaigns by conservationists, over 250,000 pups are still culled every year. Harp seals are also hunted by sharks, polar bears, and killer whales.

three times heavier than females— a difference exceeded by few other true seals. When not hunting for their usual diet of fish, gray seals spend their time either resting on rocks or “bottling”—sleeping in the water with their bodies vertical and their nostrils just above the surface. They breed onshore, hauling themselves out onto beaches or grass farther inland. Their pups have a white natal coat, and they stay onshore for two to three months before venturing into the sea.

The gray seal has a distinctive convex muzzle, which gives it a “Romannosed” appearance. Adults vary in color: males are usually gray overall, with pale patches on their undersides, while females often have a marbled pattern of dark patches over a much lighter background. Males may be two or

ORDER CARNIVORA

Mediterranean Monk Seal OCEAN LIFE

itself, where it digs breathing holes. It can dive for over an hour, feeding on fish and zooplankton. Female ringed seals breed on the ice, where they dig dens in the snow. These seals are a favorite prey of polar bears, which hunt them in their dens and when they surface to breathe.

Monachus monachus 81/4–9 ft (2.5–2.7 m)

LENGTH

550–660 lb (250–300 kg)

WEIGHT

Rocky coasts in warm-water regions

HABITAT

Atlantic coast of North Africa, Mediterranean

DISTRIBUTION

Both of the two species of Monachus seals are endangered. The larger of the two, the Mediterranean monk seal, is listed by the IUCN as critically endangered. Its coat varies from dark brown to light tan. Females are larger than males, and the pups, unusually for seals, are born with black fur. This seal was once common, but centuries of hunting and disturbance have reduced its population to a few hundred. Most exist in the Mediterranean, but the largest colony is on the Atlantic coast of Morocco. Its closest living relative is the rare Hawaiian monk seal.

MAMMALS ORDER CARNIVORA

Northern Elephant Seal Mirounga angustirostris LENGTH

10–161/2 ft

(3–5 m) WEIGHT 2,000–6,000 lb (900–2,700 kg)

Islands in deep water off rocky coasts

HABITAT

DISTRIBUTION Pacific coast of North America, from San Francisco to Baja California

ORDER CARNIVORA

Weddell Seal Leptonychotes weddellii 81/4–91/2 ft (2.5–2.9 m)

LENGTH

880–1,300 lb (400–600 kg)

WEIGHT

Polar waters around sea ice

HABITAT

DISTRIBUTION Southern Ocean, extending northward to South Georgia

The Weddell seal is found around the entire coast of Antarctica and is the world’s most southerly marine mammal. Its head looks small in

407

FIGHTING MALES Elephant seals have a winnertakes-all breeding system, in which rival males battle for the right to mate. During these contests, the two rivals face each other and then rear up, roaring noisily with their trunks inflated. They then lunge at each other with their teeth, often inflicting deep, scarring cuts. Winning males may mate with dozens of females during the course of the breeding season, while consistent losers do not mate at all.

Male elephant seals are the largest of all pinnipeds, and the colossal males dwarf the females. There are two species, one in each hemisphere. They are very similar in appearance and have similar life histories. The northern elephant seal is gray or brown, with no obvious markings. The male has a huge, muscular neck, powerful jaws, and an inflatable proboscis resembling a shortened

trunk. Both sexes have a layer of insulating blubber and a short, stiff coat, without any soft underfur. They are superb divers: the northern species has been tracked to depths of over 1 mile (1.6 km). They eat squid and deep-water fish, although it is still not clear exactly how they find their prey.

With its long muzzle and sharply constricted neck, this solitary predator looks very different from other seal species found off Antarctica. Unlike most true seals, it propels itself forward through the water with its front flippers rather than its rear ones— a characteristic that it shares with fur seals and sea lions. Its body is black or dark gray with a silvery underside, marked with darker flecks and spots. Its jaws are exceptionally powerful, with an unusually wide gape, and they are armed with long incisors and

canine teeth, as well as elaborate cheek teeth that can strain food from the water. About half of the leopard seal’s diet consists of krill, but the remainder is made up of much larger animals that it hunts individually. For example, leopard seals are adept at catching penguins as they enter the water, throwing them into the air to rip the skin and feathers from their bodies. They also prey on squid, fish, and other seals. Females give birth to a single pup each year, weaning it at the age of four weeks.

proportion to its body, and it has a short, dense coat of bluish black fur, with light streaks on the sides. It feeds mainly on fish, diving to depths of 2,000 ft (600 m), and is able to stay underwater for up to an hour. Weddell seals are so well adapted to life in cold water that they bask on ice in preference to bare ground. They breed on ice, and their winter survival depends on keeping open their breathing holes. They gouge these out with their canine teeth, starting when the ice is thin, and maintaining them as the ice thickens, to depths of up to 61/2 ft (2 m).

ORDER CARNIVORA

Crabeater Seal Lobodon carcinophagus 61/2–8 ft (2–2.4 m)

LENGTH

440–660 lb (200–300 kg)

WEIGHT

Polar waters around sea ice

HABITAT

DISTRIBUTION Southern Ocean and adjoining regions north of the Antarctic Convergence

ORDER CARNIVORA

Leopard Seal Hydrurga leptonyx LENGTH 81/2–101/2 ft (2.5–3.2 m) WEIGHT 440–1,000 lb (200–450 kg) HABITAT Polar waters, rocky coasts

Southern Ocean and adjoining regions north of the Antarctic Convergence

DISTRIBUTION

OCEAN LIFE

Despite its name, this seal feeds only on krill and other planktonic animals. It filters water using its strange molar teeth, which have elongated cusps that look like a set of stubby fingers. When its jaws close, the cusps act like a sieve, letting water out but keeping food in. Crabeater seals have slender bodies, with fur that may be light or dark brown and darker flippers. They live close to pack ice and breed on it, and they are extremely nimble on land. Their mummified remains have been found over 30 miles (50 km) inland in Antarctica’s Dry Valleys. Their total population is thought to be 10–20 million, making them more numerous than all other seal species combined.

408

ANIMAL LIFE ORDER CETACEA

Northern Right Whale Eubalaena glacialis LENGTH 43–56 ft (13–17 m) WEIGHT 33–88 tons (30–80 metric tons)

Temperate and subpolar waters

HABITAT

DISTRIBUTION Northwestern Atlantic, vestigial populations in northeastern Atlantic and Pacific

The northern right whale was one of the first whales to be hunted commercially and is now one of the most critically endangered species,

with a total population of about 500 individuals. A deep bluish black, apart from white markings on its belly, it has a deeply arched mouth, with a lower jaw shaped like a gigantic scoop. Its head its covered with distinctive areas of hard pale skin, known as callosities, which scientists use to identify individuals. Like all baleen whales, it feeds by filtering food from seawater, using brushlike strips of baleen that hang from its upper jaw. Northern right whales feed at high latitudes, but they migrate to warmer waters to breed. An almost identical species, the southern right whale, is found in the Southern Hemisphere. Unlike its northern counterpart, its numbers are gradually increasing and are currently estimated to be about 5,000.

HUMAN IMPACT

WHALING Commercial whaling has exploited many species. The northern right whale was one of the first to be seriously affected. This whale was decimated by Basque whalers who then

expanded operations to Canada in the 1500s. The sperm whale was the quarry of American whalers in the Pacific from the 1780s. Modern whaling, targeting species such as the blue whale, expanded rapidly in the 20th century, using factory ships and explosive harpoons. WHALING STATION

Hauled ashore in the Southern Ocean, a whale is flensed, or stripped of its blubber and flesh.

ORDER CETACEA

ORDER CETACEA

Bowhead Whale

Gray Whale

Balaena mysticetus

Eschrichtius robustus

LENGTH

45–60 ft (14–18 m)

LENGTH

40–50 ft (12–15 m)

WEIGHT 55–65 tons (50–60 metric tons)

WEIGHT

Polar and subpolar waters

HABITAT

17–39 tons (15–35 metric tons)

Temperate and subpolar coastal waters

HABITAT

DISTRIBUTION Arctic Ocean, Bering Sea, adjoining regions of north Atlantic and north Pacific

OCEAN LIFE

Named after its arching lower jaw, the bowhead has the longest baleen plates of any whale at up to 15 ft (4.5 m). Grayish black with a paler chin, it has a huge head in proportion to its body and remarkably thick blubber, which insulates it in near-freezing water. Bowheads can break upward through ice over 12 in (30 cm) thick, allowing them to maintain open water holes throughout the Arctic winter.

DISTRIBUTION

North Pacific, Bering Sea,

Arctic Ocean

Unlike other baleen whales, the gray whale feeds on the sea floor, filtering animals out of the sediment. Its body is gray with white mottling, and it has a narrowish head, with yellowish baleen plates up

to 16 in (40 cm) long. Its entire body is often heavily encrusted with barnacles and whale lice. Although gray whales stay close to the coast, they carry out record-breaking migrations. On the west coast of North America, large numbers migrate between the Bering Sea and Baja California in Mexico, a round trip of up to 12,400 miles (20,000 km). Unfortunately, their coast-hugging habits make them easy prey for whalers. By the mid-1900s, they had been almost wiped out, but legal protection has allowed their numbers to recover.

ORDER CETACEA

Humpback Whale Megaptera novaeangliae 40–50 ft (12–15 m)

LENGTH

27–33 tons (25–30 metric tons)

WEIGHT

Open oceans, from subpolar to tropical

HABITAT

DISTRIBUTION

Worldwide, except extreme north

and south

The humpback’s lively behavior makes it a favorite with whalewatchers. This whale has a blue-black body, deeply notched tail fins (flukes) and extremely long, winglike flippers. Its flukes and flippers are often splashed with white markings—the pattern, unique as a fingerprint, is used to identify individuals. Unlike most baleen whales, humpbacks often trap their prey by lunging upward from below. To concentrate shoals of fish or krill, they often spiral around them while exhaling air. This “bubblenetting” may be carried out by several individuals working as a team. Humpbacks spend the summer in cold, food-rich waters, moving to lower latitudes to give birth in winter. They often feed near coasts. Although protected, current humpback populations are about a fifth of those of pre-whaling days.

409 ORDER CETACEA

Minke Whale Balaenoptera acutorostrata 23–33 ft (7–10 m)

LENGTH

5–11 tons (5–10 metric tons)

WEIGHT

Open ocean and coastal waters

HABITAT

DISTRIBUTION

Worldwide, except extreme north

and south

This is the smallest of the rorquals— a name given to baleen whales that have expandable, pleated throats. It is also the most numerous, with a global population as high as 1 million. Like its much larger relative, the blue whale, it has a torpedo-shaped body with a single dorsal fin set far back, toward its tail. It is gray or brown above, with a paler underside, and short, pointed flippers that may have a white band. Minke whales live alone or in small groups. They are naturally inquisitive and regularly approach boats. They eat small fish and planktonic animals and, like other rorquals, they feed mainly in coldwater regions, eating much less during the breeding season, when they migrate toward the tropics. The minke is the only rorqual that is still hunted commercially, despite a moratorium observed by most member countries of the International Whaling Commission (IWC).

WHALE SONG

OCEAN LIFE

Like all whales, mature male humpbacks use sound to communicate. They produce the longest, most complex sound sequences of any animal, with each “song” lasting up to 30 minutes. The song is heard miles away by other humpbacks. Each regional population has its own song, sung only in the breeding season. To sing, the whale vibrates air inside itself, but exactly how is not known, because whales have no vocal cords.

HUMPBACK WHALE

In common with all baleen whales, the humpback whale has large jaws and a long head in relation to the rest of its body. It has widely spaced throat grooves and knoblike projections on the upper and lower jaws. Despite its great size, it is an energetic swimmer and often breaches spectacularly.

412

ANIMAL LIFE ORDER CETACEA

Blue Whale Balaenoptera musculus 80–90 ft (24–27 m) LENGTH

WEIGHT Up to 132 tons (120 metric tons) HABITAT

Open ocean

DISTRIBUTION Tropical, temperate, subpolar waters worldwide, except in regions with permanent sea ice

The blue whale, one of the rorqual whales, is probably the largest animal that has ever lived. Its heart is the size of a small car and its call, at about

ORDER CETACEA

Sperm Whale Physeter macrocephalus LENGTH

Up to 65 ft (20 m)

Up to 55 tons (50 metric tons) WEIGHT

Deep water, especially close to edges of continental shelves

HABITAT

DISTRIBUTION

Worldwide, except extreme north

OCEAN LIFE

and south

The largest toothed whale, the sperm whale is also the largest predator that hunts individual prey. Even in poor light, it is unmistakable, with a huge, square-ended head. Adult males are typically 13 ft (4 m) longer than females and twice as heavy. This species has wrinkled skin and a row of knobby projections between its dorsal fin and its tail. It dives to over 9,800 ft (3,000 m) to hunt giant squid. Its head contains a store of a waxy oil called spermaceti, which is thought to act as a buoyancy regulator.The oil may also help to focus beams of high-pitched sound, which the whale uses to detect its prey.

180 decibels, is louder than the sound of a jet aircraft taking off. This animal’s future hangs in the balance after decades of whaling. Although it is no longer hunted, it remains seriously endangered. The blue whale has a flattened head, a pointed snout, and a pleated, expandable throat. The rest of the body tapers to a pair of enormous tail fins (flukes). Blue whales are a mottled blue mixed with gray on their backs, but their undersides vary from white to yellow. They feed by filtering small animals, mostly krill and other small crustaceans, from the water. Their baleen plates can collect over 6,600 lb (3,000 kg) of food a day. Females give birth to a single calf every 2–3 years.

BALEEN Instead of teeth, baleen whales have flexible strips of baleen, or whalebone, which hang from the upper jaw. To feed, the whale takes in a mouthful of water, then sieves it through its baleen. The water is expelled, leaving small animals trapped, which the whale then swallows. BALEEN STRIPS

Baleen strips are made of keratin, like human fingernails. The inner face of each strip is divided into hundreds of parallel fibres.

smooth outer face

fringed inner face

413 ORDER CETACEA

Cuvier’s Beaked Whale Ziphius cavirostris 18–23 ft (5.5–7 m)

LENGTH

Up to 3.3 tons (3 metric tons)

WEIGHT

HABITAT

Deep water

DISTRIBUTION Tropical, subtropical, and temperate waters worldwide, except in far north and south

There are at least 20 species of beaked whales, but little is known about most of them. Cuvier’s beaked whale is probably one of the most widespread, because stranded specimens have been found in many parts of the world.

Like its relatives, it has an almost cylindrical body, a small dorsal fin placed far back, and relatively short flippers for its size. Its jaws are short and beaklike, with an upturned mouthline. Females are toothless, but in males, the lower jaw has two peglike teeth at its tip, which project when the mouth is closed. The overall color varies from gray and dark brown to yellow, with a swirling pattern of darker markings. Cuvier’s beaked whale lives in deep water and can dive for more than half an hour. Its feeding behavior is poorly known, apart from the fact that it preys on squid and fish. It has never been hunted commercially, but it is occasionally an accidental bycatch in fishing nets, an occurrence that has become more common with the spread of deep-water trawling.

MASSED RANKS

ORDER CETACEA

Northern Bottlenose Whale Hyperoodon ampullatus 28–33 ft (8.5–10 m)

LENGTH

Up to 8.3 tons (7.5 metric tons)

WEIGHT

HABITAT

Deep water

DISTRIBUTION Arctic Ocean, temperate and subpolar waters of the north Atlantic

One of the largest beaked whales, this species has a gray body and a bulbous forehead, which sometimes overhangs its jaws. Males have two to four teeth, at the tip of the lower jaw; females rarely have any. Its tail fins (flukes) are large and powerful, but the front flippers are unusually small and set far forward, just behind the head. These whales are exceptionally good divers, capable of staying underwater for over two hours. Unlike other beaked whales, this species was commercially hunted for many years, but it is still locally abundant.

During the breeding season, belugas gather in herds that may be thousands strong. Within each herd, the whales are grouped according to age and sex, with pregnant and nursing mothers staying close together with their young. Belugas communicate using sound, but they can also make facial expressions—a unique attribute among whales. They also often hunt in groups. ORDER CETACEA

Beluga Whale Delphinapterus leucas LENGTH

13–161/2 ft

(4– 5 m) ORDER CETACEA

Narwhal Monodon monoceros LENGTH

13–161/2 ft

(4–5 m) Up to 1.7 tons (1.5 metric tons)

WEIGHT

Polar waters, open leads in sea ice

HABITAT

The male narwhal is instantly recognizable by its unicorn-like tusk, which is up to 10 ft (3 m) long. A highly modified upper tooth,

WEIGHT Up to 1.7 tons (1.5 metric tons)

Coastal waters, sometimes rivers

HABITAT

DISTRIBUTION Arctic Ocean, Bering Sea, Sea of Okhotsk, Hudson Bay, Gulf of St. Lawrence

With its distinctive, yellowish white coloration, the beluga or white whale is easy to identify. In overall shape it is similar to its close relative the narwhal (see left), although it has no tusk. Its color changes with age: newborn belugas are dark gray, and it can take them up to ten years to assume the adult color, which comes with sexual maturity. Belugas are slow swimmers and feed on a wide variety of fish and other animals. They often live close inshore during summer months and may enter the lower reaches of large

rivers. They are remarkably sociable and vocal, making a range of different sounds, including trills, clicks, and chirps. In the days of wooden sailing-ships, these sounds were easily audible through hulls—earning belugas the nickname “canary of the seas.” Formerly abundant throughout the Arctic, belugas have been reduced to localized populations by centuries of hunting. They are still hunted today, although on a reduced scale, but they face growing threats from pollution and shipping traffic.

OCEAN LIFE

DISTRIBUTION Arctic Ocean, north as far as Svalbard and Franz Josef Land

the tusk emerges through the animal’s upper lip, developing spiral grooves as it grows. Apart from this outstanding feature, males and females are similar, with a long cylindrical body, a bulbous head, and very short, beaklike jaws. They are dappled gray above and pale or white beneath. The function of the narwhal’s tusk is unclear. It may be used for ritual combat during the breeding season, or even as a navigational aid, as it is packed with nerves.

414

ANIMAL LIFE ORDER CETACEA

ORDER CETACEA

Indo-Pacific Humpback Dolphin

Common Bottlenose Dolphin

Sousa chinensis

Tursiops truncatus 61/2 –91/4 ft (2–2.8 m) LENGTH

WEIGHT

LENGTH

Up to 440 lb

WEIGHT

(200 kg)

(650 kg)

Coastal waters, lagoons, estuaries

HABITAT

This warm-water dolphin gets its name from the conspicuous hump beneath its dorsal fin. Generally seen alone or in pairs, it shows a wide variation in color—some specimens are bluish gray, while others are almost white, particularly when they age. It feeds on fish, octopus, and squid, and it rarely strays far from the shore. A similar species exists off the Atlantic coast of Africa, and both species roll their bodies when they breathe, instead of jumping clear of the water.

ORDER CETACEA

DISTRIBUTION

Temperate and tropical regions

worldwide

A familiar sight worldwide in marine aquariums, the common bottlenose dolphin is a playful and inquisitive mammal, with a habit of interacting with humans in the wild. Its color varies from slate blue to light gray, with a paler underside. It has a pronounced beak, a slightly hooked dorsal fin, and up to 25 pairs of peglike teeth in each jaw. These dolphins are highly sociable and often travel in groups of several dozen. Like other dolphins, they find their prey by echolocation, but they also use sound to communicate, using a complex repertoire of whistles, clicks, and squeaks. They frequently ride the bow-waves of ships, and they also play with human swimmers. Females give birth to a single calf every 2−3 years.

ORDER CETACEA

Long-snouted Spinner Dolphin

Short-beaked Common Dolphin

Stenella longirostris

Delphinus delphis

41/4 –7 ft (1.3–2.1 m)

51/2–8 ft (1.7–2.4 m)

LENGTH

WEIGHT

LENGTH

Up to 165 lb

WEIGHT

(75 kg) HABITAT

DISTRIBUTION

Up to 240 lb

(110 kg) Open oceans

Tropical and subtropical waters

worldwide

OCEAN LIFE

Up to 1,450 lb

Coastal waters, open oceans

HABITAT

DISTRIBUTION Red Sea, Persian Gulf, Indian Ocean, and southwestern Pacific

61/2–13 ft

(2–4 m)

Graceful, energetic, and highly acrobatic, this dolphin gets its name from its habit of leaping out of the water and then spinning around up to seven times before splashing back into the sea. Smaller than many other oceanic dolphins, it is dark gray with white on its underside—the white varies from a small patch to a wide zone extending from its head almost to its tail. It has up to 64 pairs of teeth in each jaw, and it feeds on fish, often far out to sea. Females give birth to a single calf, suckling it for up to two years. Spinner dolphins are sociable, swimming in groups that range in size from less than 50 to several thousand and often traveling with other species. These dolphins and their close relatives often swim in large groups above shoals of yellowfin tuna, and thousands are drowned every year in purse-seine nets, which are intended to catch tuna but trap other marine life indiscriminately.

Coastal waters, open oceans

HABITAT

Temperate, subtropical, and tropical waters worldwide DISTRIBUTION

The short-beaked common dolphin is beautifully marked with a complex pattern of colored bands and has inspired artists since classical times.

Its markings are extremely variable, and it is only in recent years that it has been separated from the similar Long-beaked common dolphin, which has a more restricted distribution. Often seen in large groups, this dolphin is highly active and acrobatic, and is among the fastest swimmers of all cetaceans, with a top speed of about 25 mph (40 kph). Short-beaked common dolphins usually feed far out to sea, where they prey on squid and small fish. Adult females give birth every 2–3 years. This dolphin is one of the most common cetaceans and has a global population estimated at several million. However, like other oceanic dolphins, it is threatened by both the expansion of fishing and deliberate hunting.

ORDER CETACEA

Risso’s Dolphin Grampus griseus 10–14 ft (3–4.3 m)

LENGTH

WEIGHT

Up to 1,100 lb

(500 kg) HABITAT

DISTRIBUTION

Deep water

Tropical and warm-temperate waters

worldwide

Also known as the gray grampus, this large dolphin is typically blackish blue with a square head that is quite different from the pointed heads of beaked dolphins. Close up, this dolphin’s skin often appears scarred, especially in older individuals. Scarring is mainly due to fights between rivals, but some of it is due to encounters with squid, which make up a large proportion of its prey. When feeding, it can dive for up to half an hour. Risso’s dolphin is less sociable than many other dolphins, but it often swims alongside ships.

MAMMALS ORDER CETACEA

Killer Whale Orcinus orca 18–30 ft (5.5–9 m)

LENGTH

Up to 10 tons (9 metric tons)

WEIGHT

Open waters, areas of broken sea ice

HABITAT

DISTRIBUTION

worldwide

Tropical, temperate, and polar waters

With its conspicuous black-and-white markings, the killer whale, or orca, is—despite its name—the largest and most striking member of the dolphin family (Delphinidae). Apart from its bold patterning, its most eye-catching feature is its huge dorsal fin, which is up to 6 ft (1.8 m) high in older males. It has large, paddle-shaped flippers and a massive, barrel-shaped body that tapers toward streamlined jaws, which are armed with interlocking teeth up to 2 in (5 cm) long. Killer whales are the largest hunters of warm-blooded

prey. Their diet includes fish, squid, birds, seals, and other whales. Their hunting strategy is remarkably varied: they deliberately upend ice floes to tip seals into the sea, and they even lunge onto beaches to catch seals lying near the waterline. Intelligent, vocal, and highly sociable, they live in stable groups (pods), which develops their own cultural characteristics. Despite their ferocity toward prey animals, killer whales are easily tamed in captivity and have never been known to attack humans in the wild.

415

PODS AND CLANS An average killer whale pod contains 20 animals, which stay together for life, often sharing care of the young. Pods within the same geographical range make up a clan—a regional group that is thought to have a distinctive “dialect” that is passed on from adults to their young.

OCEAN LIFE

ON THE MOVE

Female humpback whales typically breed every 2–3 years. The mother is very protective of her calf, which she suckles for 10–11 months.

417

Whale Migration WHALE BEHAVIOR

FEEDING

ALASKAN FEEDING GROUNDS Humpback whales feed by scooping water into their huge mouths, from which they mostly filter krill and other large zooplankton. In Alaska, however, they gather close inshore in summer to feed on shoals of fish.

BUBBLE-NETTING A group of humpback whales swims slowly around a fish shoal, releasing bubbles, which form a net. Then, one whale bursts up through the bubble spiral to snatch a mouthful of fish. SOLITARY BLUE WHALE Although blue whales are known to make major migrations, they swim farther offshore than other migratory whales and do not have defined breeding areas, so their migration is less well understood.

MIGRATING

Many land mammals make long treks in search of existing feeding grounds, but the distances they cover are dwarfed by the vast annual journeys made by some whale species. Humpback whales, for example, spend the summer in rich feeding grounds in cold waters (see below), gorging themselves on krill, zooplankton, and fish. With the onset of winter, their food supply dwindles, and they migrate towards the equator. In these waters, there is little for the whales to feed on, and they fast for several months. However, these warm and sheltered waters provide a suitable environment in which to give birth and begin to rear their calves. Whale migration is a complex subject, and it is only in recent years—with the advent of satellite radio-tracking—that is has become possible to chart the path of individual animals, uncovering their migration routes. Some whales, such as bowheads and narwhals, migrate only a limited distance, staying in Arctic waters but moving in step with seasonal changes in the sea ice. In other species, migration routes are much longer, and they vary among different populations: humpback whales are a good example of this. Killer whales show a mixed pattern of migration. “Resident” pods move very little during the course of the year, but others can migrate thousands of miles. It is not known precisely how whales navigate on these long journeys. Although the mechanism is unclear, magnetite (an oxide of iron) has been found in tissues around the brains of some cetaceans, including humpbacks. It is thought that this helps the whales to sense gradients in the Earth’s eomagnetic field, which in turn acts as a guide to navigation.

SPY-HOPPING Many whales, such as this gray whale, “spy-hop,” rising vertically in the water with the head well above the surface. They may be checking for landmarks while migrating.

Humpback Whale Migration Humpback whales from the Northern Hemisphere spend the summer in feeding grounds in the northern Pacific and Atlantic oceans. In winter, these whales migrate south to warmer waters to breed. Humpback whales from the Southern Hemisphere feed in waters off Antarctica and breed in warmer waters off Australia, the Pacific islands, southern Africa, or South America. The northern Indian Ocean population may be resident all year. possible migration

major feeding areas (summer)

major breeding areas (winter)

N

PACIFIC OCEAN

TI C OCEAN

INDIAN OCEAN

WARM-WATER DISPLAY From June to December each year, about 3,700 southern right whales gather close to shore in bays east of the Cape Peninsula, South Africa. The females give birth to a single calf in these waters, then mate immediately afterward. The area offers the best land-based whale-watching in the world, providing spectacular views, such as this whale breaching. CLOSE ENCOUNTER Whalewatching is a growth industry that is worth over $1 billion a year, with over 11 million people taking part. These tourists are observing a gray whale in its summer breeding grounds in the waters off Baja California, Mexico.

OCEAN LIFE

AT L A

PACIFIC OCEAN

WHALE-WATCHING

BREEDING

main migration

418

ANIMAL LIFE ORDER CETACEA

Long-finned Pilot Whale Globicephala melas LENGTH 111/2 –23 ft (3.5–7 m) WEIGHT Up to 3.8 tons (3.5 metric tons)

Cold coastal waters, open oceans

HABITAT

DISTRIBUTION Temperate and subpolar waters worldwide, except north Pacific

There are two species of pilot whales, distinguished primarily by the length of their flippers—a feature that is difficult to observe at sea. The long-finned pilot whale lives mainly in cold-water regions. It has glossy, jet black coloration, with an anchorshaped pale patch on the throat and chest. This species has a bulbous head and short jaws. Its long dorsal fin has a hooked shape in males. Its flippers have a sharp backward bend, or “elbow,” and are up to a fifth of its body length. Long-finned pilot whales feed mainly on deep-water

squid and octopus. They are highly gregarious, living in groups that can be hundreds strong, and often associate with other cetaceans. They easily become disoriented in shallow coastal waters, often becoming stranded in large numbers. This tendency to herd together has been exploited for centuries by whale hunters, who were able to drive them into shallow water for slaughter. In some locations—such as the Faroe Islands—pilot whales are still hunted today.

ORDER SIRENIA

West African Manatee Trichechus senegalensis LENGTH

10–13 ft (3–4 m)

WEIGHT

Up to 1,100 lb

(500 kg) Mangrove swamps, lagoons, inland waterways, estuaries

HABITAT

DISTRIBUTION

ORDER CETACEA

Harbor Porpoise Phocoena phocoena LENGTH 41/2 –61/2 ft (1.4–2 m) WEIGHT

Up to 145 lb

OCEAN LIFE

(65 kg) Coastal waters, tidal regions of rivers

HABITAT

DISTRIBUTION Cold-temperate and subpolar waters in Northern Hemisphere

One of the most common cetaceans in the Northern Hemisphere, the harbor porpoise, as its name suggests, rarely strays into deep water. It prefers shallow, coastal waters and sometimes

swims into rivers. It has a short, barrellike body, with small flippers and a blunt dorsal fin. Its overall color is dark gray, while its underside is paler. Unlike most dolphins, this porpoise has a blunt snout, which houses 21–28 pairs of spade-shaped teeth in each jaw. Harbor porpoises often live alone, or sometimes in pairs or small groups; they feed on fish and shellfish. Females give birth after a gestation period of up to 11 months, and the single calf is tiny by cetacean standards, weighing as little as 13 lb (6 kg). In the past, harbor porpoises were often hunted for meat and as a source of oil. Today, a greater threat is posed by fishing nets—being small, it is easy for them to become accidentally trapped.

West Africa, from Senegal to Angola

One of three species of manatees, this docile vegetarian lives mainly in fresh water but also feeds in the mangrove swamps on Africa’s west coast. It has a barrel-shaped body covered in coarse gray skin and front flippers with tiny nails. Like all sirenians, it has no hind limbs and swims with its spoon-shaped tail, which slowly beats up and down as it cruises through the shallows. Using its fleshy lips, it feeds on plants above and below the water line. Manatees lack the complex stomachs of terrestrial plant-eaters such as cattle and antelopes. Most digestion occurs in their intestines, which may be 150 ft (45 m) long. West African manatees live in groups of up to six and give birth to young about 3 ft (1 m) long. Their slow reproductive rate makes them vulnerable to environmental change, and to hunters who target them for meat and skin.

STRANDING Pilot whales often become stranded on beaches. If one whale strands, others frequently follow, leading to a mass stranding. Theories to explain stranding involve factors that disrupt the whales’ navigational systems, such as temporary anomalies in Earth’s magnetic field, ships’ sonar, sickness, and storms.

419 ORDER SIRENIA

West Indian Manatee Trichechus manatus 12–15 ft (3.7–4.6 m)

LENGTH

Up to 3,500 lb (1,600 kg)

WEIGHT

Coastal waters, inland waterways

HABITAT

DISTRIBUTION Western Atlantic from southeast US to northeast South America, Caribbean Sea

This is the largest species of manatee, and also the best studied—something explained partly by its distribution, which extends northward as far as Florida. Unlike the West African manatee, it often ventures into coastal waters, although it avoids regions where the winter temperature drops below 68˚F (20˚C). Its skin is gray, but

its upper surface is often colonized by algae, which gives it a greenish tinge. Its vision and hearing, provided by small eyes and ears, are not very acute, but its mobile lips are covered with sensitive bristles, which it uses to find underwater plants in depths of up to about 13 ft (4 m). It needs to consume approximately one-quarter of its body weight in food each day. Although its diet is mainly vegetarian, it sometimes eats fish to obtain protein. Manatees and dugongs (see below) owe their blimplike shapes partly to the large amounts of gas generated as they digest their food. To compensate for this, they have unusually dense bones, which help them to maintain neutral buoyancy. West Indian manatees usually live in groups of up to 20 animals, and when food is plentiful, groups may increase to over a hundred individuals.

HUMAN IMPACT

COLLISION RISK In the past, West Indian manatees were hunted for their meat, skin, and oil, which was sometimes used in lamps. Today, the main threats facing them are pollution and collisions with boats. In Florida, where boat traffic is heavy, many manatees bear the scars of their encounters with boats. PROPELLER INJURY

These parallel scars on a manatee’s back were caused by a propeller. Fortunately, the cuts were not deep enough to be fatal.

ORDER SIRENIA

STELLER’S SEA COW

Dugong Dugong dugon LENGTH

8–13 ft (2.5–4 m)

550–1,900 lb (250–900 kg)

WEIGHT

Coastal shallows, lagoons, estuaries

HABITAT

DISTRIBUTION Indian Ocean and western Pacific, from East Africa to South Pacific islands

ARTIST’S IMPRESSION

Steller’s sea cow weighed up to 11 tons (10 metric tons) and was probably the largest marine mammal of its time, after whales.

OCEAN LIFE

Unlike manatees, the dugong is essentially a marine animal, grazing in seagrass beds in warm, shallow waters. Its body is blimp-shaped, like that of manatees, but it has a crescent-shaped tail and a broad head with a large, U-shaped upper lip. Part of its diet consists of buried stems or rhizomes, which it collects by nuzzling its way into the sediment, while steadying itself with its front flippers. Dugongs feed in scattered herds, which may contain more than a hundred animals. Their main predators are sharks, but they are more threatened by hunting in many places. The species is already extinct in the Mediterranean, where it may have existed until classical times, and it is under threat in many parts of the Indian Ocean. However, it appears to be thriving around the coastline of Australia, which is home to over half the world’s dugongs.

A close relative of the dugong, Steller’s sea cow lived in the icy waters of the Bering Sea, feeding on kelp and other seaweeds. It was hunted to extinction in 1768, 27 years after it was first recorded by the German naturalist Georg Steller (1709–46).

ATLAS OF THE OCEANS

OCEANS OF THE WORLD

Oceans of The World

There are five oceans separating the world’s major landmasses, and numerous marginal seas, gulfs, and connecting straits. The continents are surrounded by shallow shelves, which extend a variable distance from the shore before descending into the deep ocean basins. The ocean basins contain the flattest parts of Earth’s surface— the abyssal plains—but also the greatest extremes of elevation, from deep ocean trenches to the peaks of the world’s largest volcanoes. The

OCEANS COVER 71 PERCENT of Earth’s surface and contain 97 percent of its water. The geography

of the ocean basins tells us much about Earth’s past and the geological forces that continue to shape the world. 90ºE

60ºE

120ºE 3,849m (12,629ft)

Nansen Basin Severnaya Zemyla

Franz Josef Land 5m (16ft)

Nemaya Zemyla

Barents Sea

73m (240ft)

Ber ing S trait

Chukchi Sea

Le

ch na

c ad i ve Platea u os–L ac

Chag

Andaman Sea ast

Indi

Tasmania

South Australian Plain 5,386m (17,671ft)

n

Pl

ea

u

SCALE

Mu rray

South Australian Basin

an R idge

le

arling

Tasman Sea 5,369m (17,616ft)

s

i

a

N orth Fiji Fiji Basin

South Fiji Basin

New Zealand

95m (312ft)

ic–

5,415m (17,677ft)

Anta

A NTA R C T I C A 2,000

10,800m (35,435ft)

ge

Cam pbell Plateau

Pa c i f

South Indian Basin

Antarctic Circle

1,000 1,500 2,000 2,500 K m

6,249m (20,503ft)

Ton Tren ga ch

ar

Mid-Indian Ridge

anne l

g as c

e Ch

Mad a

mbiq u Moza

Ninetyeast R idge

he

1,577m (5,174ft)

e

e rctic Ridg

Ross Sea

2,500 Miles

Ross Ice Shelf 30ºE

60ºE

90ºE

120ºE

150ºE

d Ri

ue

ut

4,890m (16,339ft)

Central Pacific Basin

e ill isv Lou

D

ntains

e Ris

Mada gas Plate aucar

AU S T R A L I A

n

Lord Howe

Perth Basin

S OU T H ERN OCE AN

1,500

Ba rri er

an e Tasmure Zon Fract

rg

at

Enderby (17,671ft) Plain

1,000

e l Bismarck a Sea New Banda Guinea Sea Solomon Arafura Sea Timor Sea Sea Coral Sea

5,678m (18,636ft)

fic Mo u

M elan esian B asin

ef Re

Mozam Plateabuique

Java Sea Ja va 7,125m

Mid -Paci

Ridg e

PA C I F I C

at Gre

So

Mackenzie Bay

500

Celebes

Ha w aiian

Micron esi a

M

Great Australian Bight

Crozet Basin

5,386m

500

Celebes Sea

Java (23,377ft) Trench Wharton Basin

en Ridg e

6,464m (21,208ft)

Sea

4,936m (16,195ft)

Ke

Atlantic– Indian 60ºS Basin

a

r

Brok

e dg

Phil ip p ine Se a Challenger

South China Basin

at

n t I

Cocos Basin

Investigator Ridge

So

Agulhas Basin

uth

s we

Ri

Mid-Indian Basin

uk Ry

Borneo

INDIAN OCEAN

2,078m (6,818ft)

n

Ceylon Plain

5,614m (18,240ft)

Madagascar Basin

a di

Sunda S h e lf

m

ene ar au e

Natal Basin

5,819m (19,092ft)

Mascarene Basin

Sri Lanka

er ak nts m u p o m 6,800m (22,311ft)

Deep Philippine 10,920m Basin (35,829ft) Philippines 10,057m ia South Marren T (32,997ft) China

Su

g er

Somali Ma Basin Pla sc t Seychelles

3,462m (11,359ft)

ng eko

4,481m (14,702ft)

4,836m (16,031ft)

Tropic of Capricorn

Bay of Bengal

Car Ridlsb ge

Equator

mbezi Za

Ganges Fan

Arabian Basin

en of Ad Gulf

A F RI CA

St ra

Arabian Sea

M

ea dS Re

Arabian Peninsula

an ges

Ta iw an

Tropic of Cancer

30ºS

gtz Yan

us

Nile

G

e

Ind

Ja Trenpan ch

s

Yellow Sea East China ti Sea Taiwan y

ch

er

r is

iv Yellow R

Northwest Pacific Basin

ts amoun

T ig

Eup hra te

r Ku

Sea of Japan/ East Sea Honshu

(23,997ft)

e eror S

Black Sea

Mediter ranean 30ºN Sea

Bering (66ft) Sea nds a l s I n Aleutia Aleutian Trench 7,184m

Ke r Tremadec nch

ASIA

20m

Aleutian Basin

Emp

Danube

Am ur

E URO PE

tka ha sula c Sea of m nin Okhotsk Ostrov d Sakhalin an h I sl nc e l i Tre Ku r 9,763m Hokkaido ile(32,098ft)

M Se a a

Ir t ysh

s K Pe a

Volg a

AT L A S O F T H E O C E A N S

East Siberian Sea

Ob’

60ºN

0

2,814m (9,233ft)

Novosibirskiye Ostrova

na

Arctic Circle

0

ARCTIC OCEAN

Laptev Sea

Kara Sea

180º

150ºE

ev ley de en ge M Ri d

30ºE 3,910m (12,829ft)

longest mountain chains on Earth are the mid-ocean ridges, which circle the planet along the boundaries of the major tectonic plates. The maps in this chapter draw on the most detailed knowledge of the topography of the global sea floor yet assembled. They combine the latest measurements from satellite altimeters with more than 100 years of shipborne hydrographic surveys to give the clearest possible portrayal of the shape of the sea bed.

uT re n

422

180º

3,718m (12,199ft)

Banks Island

Beaufort Sea

smer Elle

Victoria Island

Isl

an

i

Zone

Fractu re

tsev F ractur e

Zone

Ori ge

Mornington Abyssal Plain

d Frac ture Z one

Falkland Islands

6,034m (19,798ft)

Zone

Southeast Pacific Basin

ke Drsasage Bellingshausen Plain P a

Bellingshausen Sea Amundsen Sea

120ºW

Mid-A tlan tic

1,739m (5,706ft)

Argentine Basin

Scotia Sea

5,042m (16,543ft)

e ractur Gough F

30

Cape Cape Goo Basin Hop

South Georgia 7,152m (23,466ft)

ia ntic–Ind Atla Ridge

id tica R Antarc America–

ge

SOUTHE RN O CEAN

sula enin cP

60ºW

Tropic of Caprico

Zone

60º

Antarctic Circ

Weddell Plain

Weddell Sea

Ronne Ice Shelf 90ºW

Co

Angola Basin

e re Zon Fractu e d n a r G Rio

Rio Grande Rise

Challenge r Fract ure Zo ne 1,426m Chile (4,679ft) Ris e

A N TA R C T I C A 150ºW

Chile Basin

Cape Horn

4,283m (14,058ft)

en Plain Amunds

Roggeveen Basin

8,069m (26,474ft)

ne

5,706m (18,721ft)

e

Antarcti

Udin

Menar

Tr

Equat

30ºW

0º

AT L A S O F T H E O C E A N S

Southwest Pacific Basin

Eltani n

r Fracture Zone Easte

Zone

East Pa c Rise cifi

ter F ract ure

acture siz Fr Agas

Yupanqui Basin

a

e

Guinea Basin

o Brazil ture Z n Frac Basin Ascensio

isco

ch

Eas

Zone

Sierra Leone Basin

n

s

nds

re Mendaña Fractu

Peru Basin

Na zc aR id

Rise Ea s tP ac ific

Basin

e

OCEAN

ig

mazon

SOUTH AMERICA

l

Isla

n

Bauer Basin

hi

otu

Dem e Pla rara in

A

–C

y

Galapagos Islands

Peru

Tua m

AT L A N T I C

noco

Basin

3,806m (12,487ft)

Zone cture 4,567m os Fra g a p a (14,984ft) 5,451m Gal Marquesas (17,885ft) Islands Zone acture P o sas Fr e u q r l Ma Tiki

8,952m (29,404ft)

Ridge

one ure Z

Caribbean Sea

A F R I CA er

Am eric aT r Guatemala ench

Cape Verde Basin Barr acuda Cape Verde Fracture Zone Islands

o Fran c

Mid dle

Tropic of Canc

3,780m (12,402ft)

Nares Plain

Antilles

Canary Islands

N

Fract

Grea t er

S a rg a sso S ea

Par ana

e re Zon

OCEAN rt o n lippe

Hatteras Plain

Sa

o Gra

Gulf of Mexico

Norwegian Sea Arctic Circ Norwegian vi Basin ina d a n 60º Sc

r ai t k St Iceland

es jan yk asin nes Basin e Labrador Sea R B ja and l k e y Ic North Labrador Re Sea Charlie Gibbs Basin N Fracture Zone Ireland Mi orthw Britain d-O e ce s t A Newfoundland an t l 4,139m Ch an 13m (13,580ft) an tic (43ft) ne l Newfoundland Iberian Basin Plain Ocea Azores an Sea nogra phers Mediter rane Fracture e Zone Sohm 5,464m dg (17,927ft) Plain Ri Madeira 30º Plain

it tra

ai F

Ri

Zone racture

Fra ct u larion

C

ar nm De e g Rid

EUROP E

nde

Molok

C

Greenland

D

d

Spitsberg

Greenland Sea

sS

5,999m (19,683ft) one ure Z Fr a c t y a r Mur

0º

30ºW

i av

acture Zone Mendocino Fr

uncertain boundary

Sandwich Plate

Basin

Great Lakes

N O RT H AMERICA

transform boundary

16,400 ft (5,000 m)

Baffin B a y Baffin

Hudson Bay

Vancouver Island

divergent boundary

nd e Isla

Baffin

Gulf of Alaska

convergent boundary

6,500 ft (2,000 m) 9,800 ft (3,000 m)

Shetland Plate

River Yukon

Hawaiian Islands

SOUTH AMERICAN PLATE

60ºW

Queen Elizabeth Islands

maximum depth on map

3,300 ft (1,000 m)

Scotia Plate

ANTARCTIC PLATE

90ºW

1,600 ft (500 m)

AFRICAN PLATE Nazca Plate

sea depth

ng

AUSTRALIAN PLATE

120ºW

Canada Basin

PACIFIC PLATE Bismarck Cocos Plate Caroline Plate Plate Easter Plate Fiji Plate Juan Fernandez Plate

Indian Plate

seamount

800 ft (250 m)

ge

150ºW

Juan de Fuca Plate

Phillippine Plate

EURASIAN PLATE

land

Rid

Earth’s surface is split into 7 major plates and at least 15 minor ones. Their boundaries are most clearly expressed in the topography of the sea floor, where mid-ocean ridges, ocean trenches, and fracture zones represent divergent, convergent, and transform boundaries, respectively. Although some plates have continental and oceanic parts, the largest, the Pacific Plate, is only oceanic crust.

sea level

Walvi s

Arabian Plate

TECTONIC PLATES

NORTH AMERICAN PLATE Rivera Caribbean Plate Plate

Mid-Atlan tic

EURASIAN PLATE

423

KEY

Okhotsk Plate

424

A

THE ARCTIC OCEAN

B

C 150˚E

200

100

300

400

500 km

0

100

300

200

500 miles

400

Ar c

limit of sum

˚

Pevek

East Siberian Sea

Bering Sea

v oli a Pr ong L Ostrov Vrangelya

Chukotskiy Peninsula

Chukchi Sea

755m (2,477ft)

73m (240ft)

Barrow

4

pe

for tS lo

Bea u

Canada Plain 3,674m (12,054ft)

3,718m (12,199ft)

Canada Basin

Beaufort Sea

Rise

Banks 2,546m (8,353ft)

z ie ken

Pr in

3,300 ft (1,000 m) 6,500 ft (2,000 m)

Ocean Floor

9,800 ft (3,000 m)

Kugluktuk

or Guona lf tio

n

5m (16ft) Cambridge Bay

Larsen Sound Queen King Maud William Gulf Island

16,400 ft (5,000 m)

land

8

seamount sea depth

Victoria Island

Stefansson (23ft) Island 338m Cornwallis

NORTH AMERICA

maximum depth on map

e Strait

1,600 ft (500 m)

McClintock Channel

Ships with strengthened bows and powerful engines—icebreakers—are needed to penetrate Arctic sea ice.

0 12

M

Vis elvi Queen Elizabeth co lle Strunt Trou ait M gh Bathurst elv ille 7m Island

Ra

˚W

800 ft (250 m)

nd ou n rt S to be las ula Al ol ins ce W en P Un hin and ion Dolp Strait C

sea level

Albert Peninsula

Ar ct 90˚W

A

B

Island

(1,168ft)

Prince of Wales Island

Pee l So un

Amundsen Trough Prince

Borden Island Mackenzie King Island Melville Lougheed Island Island

B Penoothia insu la

Banks Island

lure MctCrait S

Amundsen Gulf

Ma c

Cape Prince Cape Banks Alfred 401m Prince Patrick Cape Shelf (1,316ft) Bathurst Kellett Island

KEY

ICEBREAKER

AT L A S O F T H E O C E A N S

Beau

Prudhoe Bay

fort

She lf

Point Barrow 150˚W

e

No Chukchi rth Pla wind Plateau Mendeleyev No in Plain rth wi 3,792m nd Rid (12,442ft) ge

Ocean Circulation

The floor of the Arctic Ocean consists of two main basins separated by the sharp Lomonsov Ridge. On the North American side lie the Canada and the Makarov basins, separated by the Alpha Cordillera. On the Eurasian side the Fram and Nansen basins are split by the Gakkel Ridge—an extension of the Mid-Atlantic Ridge. The young Arctic Basin started to open about 36 million years ago, completing the separation of North America from Europe, and connecting the Arctic to the Atlantic. There is an unusually broad continental shelf on the Asian side of the ocean, with shallow seas extending more than 1,000 miles (1,600 km) from the coast in places, compared with the more typical 30–75 miles (50–125 km) on the North American side.

Me nd ele ye vR idg

Chukchi Plain

d

Resolute

Somerset Island gent e e Rt ir ncInle P

B Pen rodeu insu r la

Ko tze So bue un d

Cape Lisburne

Cape Chapman ee p so l Simninsu Pe

ic Cir cle

C

nin vill sul e a

Seward Peninsula

Gulf Boothof ia

3

n mm a i Ba tt y Pe Mel

Be Strar ing it

Sea ice covering the Arctic expands from less than 3 to about 6 million square miles (4.5 to 15 million square km) from summer to winter.

ce

Ostrov Novaya Sibir’

Co

2

mer pack i

27m (89ft)

18 0

ARCTIC SEA ICE

The Arctic receives a huge influx of fresh water from the great Siberian rivers—the Ob’,Yenisey, and Lena.Together with the freezing and melting of sea ice, this produces a layer of relatively fresh surface water. A clockwise gyre is established over the Canada Basin, while the Transpolar Current flows from the Chukchi Sea to the Greenland Sea.Warm, salty water enters the Arctic from the Atlantic at moderate depth, while very cold, very salty “bottom water” flows out into the Atlantic. Eighty percent of the Arctic’s water exchange is with the North Atlantic and 20 percent is with the Pacific. About two percent of the water leaving the Arctic is in the form of icebergs calved from the Greenland Ice Sheet. Arctic sea ice has declined in area at about 13 percent per decade since 1979, and hit a record low of 1.4 million square miles (3.63 million square km) in September 2012. Global warming could cause the ocean’s sea ice to disappear by the end of the 21st century.

iv Prol

Ambarchik

tic

THE SMALLEST OF THE OCEANS, the Arctic

Ocean is nearly enclosed by Asia, Europe, Greenland, and North America. In winter it is almost entirely covered by pack ice, which halves in area during summer. Exploration of the Arctic in the 18th and 19th centuries was driven by the search for trade routes between the Atlantic and Pacific oceans. The North Pole was first reached in 1909 by an American expedition using dogs and sleds, led by Robert Peary.

Kolym a

0

1

Ci rc le

The Arctic Ocean

SCALE

E

ASIA

e

Kvitøya

tr

Na res S

Daneborg

Qaanaaq 77m (253ft)

un Devon d

lop e

ub a

1,280m Voring (4,200ft) Plateau

ne Zo

Norwegian Trench

68m (223ft)

Upernavik

Faeroe Islands

ffi

Strait

Devo nS

Dumshaf Plain

Iceland Plateau

2,377m (7,799ft)

nd sla n I

Uummannaq

70˚N

Halten Bank

c ct i Ar

Qeqertarssuaq 60˚W

c Cir

hetland Faeroe–Sugh Tro

Ittorqqortoormiit

Baffin Bay

6 222m (738ft)

ge

Ba D

Norwegian Sea

e tur rac F n ye Jan Mayen Norwegian Ma n Basin Ja Jan Ma ye nR i dg e

Kullorsuaq

Baffin Basin

Røst Bank

Rid

Cape Devon Lan Lanccaste Sherard Shelf 732m aste r Tr r S oug (2,402ft) ou h n Bylot d Island

Bodø

F

G

0˚

Shetland Islands

Britain

Iceland

le

Reykjavík

30˚W

E

7

sey

Greenland

Island

2,580m (8,465ft)

H

I

8

AT L A S O F T H E O C E A N S

210m (689ft)

Tromsø

Kolbein

Jone s So

Greenland Sea

Denmark

m

les El

80˚N

Fugløya Bank

n rde fjo

Belgica Bank

5

t Ves

a it

3,900m (12,796ft)

Hammerfest

(843ft)

n Zo ure Greenland Fract

15m (49ft)

Speed 0–10 mph (0–16 km/h) 10–25 mph (16–40 km/h) over 25 mph (over 40 km/h)

EUROPE

North 257m Cape

ugh

Spitsbergen Fracture Zone 5,601m Knip (18,377ft) ovic hR rd e idg a a g n v o e o Z H e r Boreas u t c a r F

Beaufort Scale 0–3 3–5.5 over 5.5

30˚E

ro nts T

Longyearbyen

Bjornöya Bank Bjørnoya

SURFACE WINDS

Thor Iversen Bank

re Ba

Grise Fiord

renna rf j o r d Sto

Spitsbergen

nd e n la GrePlain

I

gh ou e Tr

re

sla

Edgeøya Barentsøya

Plain

Alert

nd

Stor Bank

Nordaustlandet

Litk

Nord

Lincoln Sea

102m (335ft)

ice

dg

Cape Columbia

Barents Sea k pac er

Ri

asin m B

ra ille

2,590m (8,498ft)

Easte r

Po lar Easte rlies

109m (358ft)

mm

el

Fra

d Cor

Yermak Plateau

Kap Morris Jesup Wandel Sea

e

170m (558ft)

Barents Plain

Lena Troug h

Islands

batskay a

at ea u

a tay gh va ou Sy a Tr n An

Franz Josef Land

3,910m (12,829ft)

ar

N o va ya Z e m lya

sin Ba

kk

e nosov Ridg

in as a Alph

North Pole

Pl

328m ova (1,076ft) y a Ze mlya Trough

f su to limi

Ga

mo

en ns Na

n lai eP Pol

Lo

vB ro ka Ma

4,484m (14,712ft)

a ar lK

st N

lies

s Westerlie

C

tra en

Ea

limit of winter pack ice

Vo r

i on

h ug ro T n

Ka Strariat s

Ostrov Komsomolets

Polar Ea ster

˚E

60

lie

ARCTIC OCEAN

ara yd u Ba G

Ostrov Belyy

Kara Sea

Ostrov Oktyabr’skoy Revolyutsii

80˚N

Alex Heiberg Island

Ob s

5m (16ft)

Zemlya

SURFACE CURRENTS

ren t

Proliv Vil’kitskogo Ostrov Severnaya Bol’shevik

3,849m (12,629ft)

1,250m (4,101ft)

Poluostrov Yamal

Dikson

rwegian Cur

G ya ka

Novosibirskiye Ostrova

No

myr strov Tay Poluo

d Cur re nlan nt ree tG Eas

Gydanskiy Poluostrov

Laptev Sea

Wrangel Plain

Transpolar Cur ren t

le

Beaufort Gyre

6m (20ft)

Ostrov Kotel’nyy

2,814m (9,233ft)

cC irc

e

Buork h Gubaaya

Tiksi

Ar c ti

90˚E

70˚N

Po l

120˚E

425

land reen st G ent We Cur r

eva Lapt itraya Dim Ostrov Bol’shoy Lyakhovskiy

a

G

Yen isey

Len

70˚N

F

Mohns Ridge

D

THE ARCTIC OCEAN

Northwest Passage are linked by the

DISCOVERY

Northwest Passage through the Arctic Ocean. A tough route to navigate, it includes many narrow straits between islands, and its surface is often frozen, even in summer. Shrinking sea ice has made it more navigable, with ice-free conditions in 2007 and 2012, and the first commercial freighter passing through in September 2013.

266,000 square miles (689,000 square km) 6,900 ft (2,100 m)

Arctic Basin, Labrador Sea, glaciers of West Greenland INFLOWS

GLACIER MEETING SEA

Current, often carrying icebergs into the North Atlantic. Seals have long been hunted in the area. Large numbers were killed each year as recently as the 1980s, but commercial hunting of marine mammals is now controlled.

Prince Patrick Island

King William Queen Maud Island Gulf

Mackenzie

Prin ce

CANADA

land seamount sea depth

4

maximum depth on map tectonic plate boundary

Rankin Inlet SCALE 0

0

100

200

100

300

200

400

500 km

300

400

500 miles

60˚N

120˚W

A

110˚W

B

100˚W

C

Uummannaq ˚N

70

2,377m (7,799ft)

Brodeur Peninsula

Ba

Boothia Peninsula

Larsen Sound

Baffin Bay

ff

in

Cape Chapman

Melville 37m Peninsula (121ft)

Prince Charles Island

Is

la

Qeqertarssuaq 2

Home Bay

n

Cumberland Peninsula 119m (390ft) 3 Cu Foxe mb Repulse erl Basin an Bay dS Cape ou a l u nd Dorchester s n Hall M eni P e e Iqaluit t Fo x Peninsula a 60˚W o F Inc xe ogn C ita Frob Southampton hannel Pen i insu sher Ba Salisbury Island y l a H Island Evans udso Resolution n St r a Strait Nottingham it Island Island Cape Ivujivik 507m Chidley 60˚N (1,663ft) Coats 4 Akpatok Péninsule 234m Island Mansel Island (768ft) Island d‘Ungava Ungava Bay Hudson Bay

t

16,400 ft (5,000 m)

Bylot Island

trai

cle

(16ft)

732m (2,402ft)

S vis Da

ulf 5m

Lancaster Sound

Upernavik

Baffin Basin

d

3,300 ft (1,000 m) 6,500 ft (2,000 m) 9,800 ft (3,000 m)

ic Cir

Coronation G

Devon Shelf

326m (1,070ft)

an ne l

Cambridge Bay

1 Kullorsuaq

Cape Sherard

Borden Peninsula

GREENLAND

77m (253ft)

Lancaster Trough

Somerset Island

50˚W

Qaanaaq

f lf o ia Guooth B

Arct

of Wales Island

Ch

Kugluktuk

1,600 ft (500 m)

AT L A S O F T H E O C E A N S

Victoria Island

Devon Island

60˚W

pe Slo

338m (1,168ft) Prince

Amundsen

GuTrough lf Do Prince Albert Sound lph in Wollaston Str and Peninsula ait

Grise Fiord Jones Sound

Resolute

Stefansson Island

ck

800 ft (250 m)

3

Viscount Melville Sound

n nio U

sea level

trait les S WaPrince f o Albert Peninsula

(23ft)

o int

KEY

Melville Trough

Peel Sound

n

Islands

Bathurst Island Cornwallis Island 7m

and

Cl Mc

2

e ds un Am

Cape limit of summer pack Kellett i 70 c e ˚N Cape Bathurst

Ellesmere Island

Par r y Islands e Isl

70˚W

n Devo

Banks Island

ur e t

Banks Shelf

Me lvill

rai St

2,546m (8,353ft)

80˚W

Alex Heiberg Island

Queen Elizabeth Islands

401m (1,316ft)

Mc Cl

90˚W

Ellef (1,152ft)Ringnes Amund Mackenzie Island Ringnes King Island Island Lougheed Sverdrup Island

se Ri

Cape Prince Alfred

100˚W

F

c le c Cir Arcti

F Strisher ait

s

110˚W

Borden Island 351m

E

Ro Soues We nd lcome

Beaufort Sea

Ba nk

3,674m (12,054ft)

120˚W

The deep Beaufort Sea lies to the west of the Canadian Arctic Archipelago. Oil was discovered off the Alaskan shore in 1968, and is also extracted off the MacKenzie delta. Artificial islands have been built to protect some production wells from drifting sea ice. Gas has also been found near Melville Island.

D

Reg ent I nlet

130˚W

Canada Basin

1

C

Prince

140˚W

15,350 ft (4,680 m)

Chukchi Sea, Arctic Basin, rivers Mackenzie, Colville

INFLOWS

Nares Stra it

B

Ra eS

A

184,000 square miles (476,000 square km)

OIL EXPLORATION

S Penimpson insul a Committee Bay

Baffin Bay lies between Greenland and Baffin Island, and is really the extreme northwest arm of the Atlantic. The surface ices over each winter, but warmer water from the Labrador Sea flows up its eastern shore, keeping parts of the adjacent Greenland coast ice-free. Water returns south along the western shore as the cold Labrador

AREA

Much effort was expended in the 17th century in search of the Northwest Passage from the Atlantic to East Asia, but no viable route was found due to the year-round presence of sea ice and the numerous islands. Interest revived in the 19th century when expeditions were undertaken by the Royal Navy. In 1820 an expedition from Baffin Bay got as far as Melville Island before being blocked by ice. A group of 129 men was lost off King William Island in 1848. British explorer Robert McClure crossed from the Beaufort Sea to Baffin Bay in 1854, but he had to walk part of the way. It was the Norwegian Roald Amundsen who finally sailed a ship via Lancaster Sound, south of Victoria Island, and out through the Bering Strait in 1906.

Baffin Bay MAXIMUM DEPTH

Beaufort Sea MAXIMUM DEPTH

ARCTIC OCEAN E2

AREA

ARCTIC OCEAN A1

EXPLORING THE PASSAGE

THE ATLANTIC AND PACIFIC OCEANS

trait

426

90˚W

80˚W

D

70˚W

E

F

0

ge

aye n Ri d 200

300

400

222m (738ft)

Ve stf jo

1,280m (4,200ft)

rait

Ostrov Kolguyev Poluostrov Kanin

Hammerfest

Røst Bank

en rd

328m (1,076ft)

Gusinaya Bank 47m (154ft) North Kanin Bank

Mu rm Ris ans e k

Tromsø

Murmansk

300

500 miles

Halten Bank

A

SWEDEN

10˚E

B

20˚E

C

The Barents Sea

THE BARENTS AND GREENLAND SEAS MARK

the boundary between the Arctic Ocean and the Atlantic. Most of the Arctic Ocean’s water exchange is with the north Atlantic. This exchange occurs at the Fram Strait, north of the Greenland Sea. ARCTIC OCEAN E2

Barents Sea 540,000 square miles (1.4 million square km)

MAXIMUM DEPTH INFLOWS

2,000 ft (600 m)

Norwegian Sea, Arctic Basin

The Barents Sea is relatively shallow, lying north of Europe and south of the islands of Svalbard and Franz Joseph Land. To the east, Novaya Zemlya is an extension of the Ural Mountains, which mark the geographical boundary between Europe and Asia. Large areas along the mainland and around the islands are continental shelf of less than 660 ft (200 m) deep. Warm water from the North Atlantic Drift flows in from the southwest, keeping most of the sea ice-free in summer. The Russian port of Murmansk

remains free of ice even in the winter. The warm, salty Atlantic water meets cold, less saline Arctic water, and warm, moderately salty coastal water, producing an area of high biological productivity. The spring bloom of phytoplankton starts near the ice edge, where fresh water from melting ice produces a stable surface layer. The phytoplankton form the basis of a food chain that supports a rich fishery, and cod is the most important catch. During the Cold War, Russia maintained a large northern fleet of warships and submarines. Many of these vessels now lie deteriorating in naval ports along the Kola Peninsula, raising fears of possible damage to the marine environment. Particular concerns have been raised about contamination from the nuclear reactors of abandoned submarines.

30˚E

D

Greenland Sea 463,000 square miles (1.2 million square km)

MAXIMUM DEPTH INFLOWS

40˚E

RUSSIAN FEDERATION

Dv ina

E

ARCTIC OCEAN B2

AREA

Archangel

16,000 ft (4,800 m)

Arctic Basin, Norwegian Sea

The Greenland Sea, which stretches between Greenland, Svarlbad, and Jan Mayen Island, is a major area of sea-ice formation in the Arctic Ocean. The East Greenland Current carries surface water and ice south along the coast of Greenland, but the Jan Mayen Current takes some surface water to the east. This divergence leaves an area of open water where new sea ice is

50˚E

F

continually formed in the winter. An ice tongue, known as the Odden, develops eastward from the main ice edge, and dissolved salt is left behind in a layer of cold, briny water beneath the new ice. Being more dense, this very salty water sinks to the seafloor, where it pools before spilling over the ridges between Greenland and Jan Mayen to the south. This downwelling plays a major role in the global thermohaline circulation (see pp.60-61) of the oceans. ICY PANCAKES

Pancake ice is formed in rough water as cakes of icy slush bump into each other, producing a raised rim.

AT L A S O F T H E O C E A N S

AREA

Circ

n

0˚

le

tic

Arc

4

her

10˚W

400

3

Nar’yan-Mar

26m (85ft)

Gu Bo lf of thn ia

200

60˚E

Bodø

Nort

100

˚N

60

Kola Peninsula

FINLAND

White Sea 0

2

a St

na

North Cape

ly a T rou

gh

Barents Sea Thor Iversen Bank

NORWAY

Voring Plateau

500 km

109m (358ft)

257m (843ft) Fugløya Bank

1

ck pa

Hopen

h ug Tro s t n Bare

Basin

Ja nM

100

ren

Bjornöya pack ice Bank t of winter limi

Norwegian Sea

170m (558ft)

Franz Josef Land

102m (335ft)

Bjørnoya

SCALE

4

rd Storfjo

Dumshaf Norwegian Plain

Kara Sea

ra

ICELAND

Stor Bank

33m (108ft)

dg e s Ri Mohn

80˚E

cho Pe

Iceland Plateau tic Circ le

70˚E

˚N

Barentsøya Edgeøya

2,580m (8,465ft)

Arc

ice

Spitsbergen Longyearbyen

ne Zo

3

Ridge sey Jan Mayen n i e

60˚E

Ch Gubeshska a ya

F

er mm u s t of limi

dge ne

e ur ct ra

lb Ko

Nordaustlandet

Greenland Sea

Ja n

Kvitøya

ich Ri

Zo

Plain

M ay en 60˚ Ittoqqortoormiit N

k Lit

Knipov

Greenland 3,900m (12,796ft)

50˚E

427

Kar

rd aa on vg Z Ho ture c Fra

e tur rac nd F Greenla

Daneborg 210m (689ft)

40˚E

h ug ro T e

SVALBARD

Boreas e Plain

2

30˚E

70

e 5,601m (18,377ft)

Belgica Bank

20˚E

F

a tay h va oug Sy a Tr n An

15m (49ft)

10˚E

E

East Novaya Zem

0˚

en rg n be Zo its re Sp ctu a Fr

GREENLAND

1

10˚W

ea u

20˚W

˚N

D

Pla t

30˚W 7 0

a Trough Len

40˚W

C

N o va y a Z e m l ya

B

Yer ma k

A

A

THE ATLANTIC OCEAN

B

C

90ºW

The Atlantic Ocean

60ºW

Ba ffi n Baffin

1 Arctic Circle

nd

Foxe Basin

Hudso n

THE ATLANTIC SEPARATES

Hu ds o n Bay

N O RT H AMERICA

2

Québec Montréal nce wre La t Toronto S

Great Lakes Detroit

Chicago

pi

New York Baltimore

3

30ºN

rande

Blake Plateau Tampa

New Orleans

Miami

Ocean Circulation

Tropic of Cancer

A clockwise gyre controls surface currents in the north Atlantic. The strong Gulf Stream current brings in warm, salty water from the Caribbean. It then continues northwestward as the North Atlantic Drift, giving western Europe a milder climate than its latitude alone allows. Some water moves north toward the Arctic Ocean, but most returns south as the Canaries Current. Warm water returns to the west with the North Equatorial and Guiana currents. The South Atlantic Gyre turns counterclockwise, with the Antarctic Circumpolar Current forming its southern boundary. The cold Benguela Current flows north up the coast of Africa. In the west, the Brazil Current flows rather weakly south from the equator.

Tampico

Gulf of Mexico

4 Labrador Current

Norwegian Current North Atlantic Drift

Gulf Stream

5

Panama Canal

Equator

Canary Current North Equatorial Current Guinea Current Equatorial Counter Current Benguela Current Agulhas Retroflection

South Equatorial Current Brazil Current Falklands Current

6

Antarctic Circumpolar Current

PACIFIC Tropic of Capricorn

OCEAN

SURFACE WINDS est W

30ºS

erlies

s de Tra E N

Doldrums

SE s de

a Tr

This image shows a trench scoured out by the keel of a drifting iceberg—a fairly common occurrence in shallow waters around Greenland.

Santo

e r Domingo An til l Caribbean e s

Cartagena

SURFACE CURRENTS

ICEBERG SCOURING

Great

Sea

The Atlantic’s high tidal range makes many locations suitable for harnessing tidal power, such as this installation off Devon, England.

The Atlantic Ocean floor is dominated by the Mid-Atlantic Ridge, marking where the continents to the east and west are splitting apart. The ridge breaks through the sea surface at some points, most notably as the island of Iceland. Transverse faults scar the flanks of the ridge for many hundreds of miles east and west, until they are buried under the marine sediments of the abyssal plains. These flat areas are quite narrow in the Atlantic, occupying the edge of the deep ocean between the broad ridge and the continental rise. The sedimentary margins of the Atlantic bear some rich mineral deposits, including oil and gas in the North Sea, the Gulf of Mexico, off Venezuela, and West Africa. The Atlantic has only two deep ocean trenches—the Puerto Rico Trench and the South Sandwich Trench.

Havana

Veracruz

TIDAL POWER

Ocean Floor

tt e r a s H aP l a i n

io G

R

ATLANTIC SURF BATTERS BERMUDA

60ºN

Mississip

the “old world” of Europe and North Africa from the “new world” of the Americas. The Portuguese pioneered the ocean’s exploration, with Bartolomeu Dias reaching Africa’s southern tip in 1488, but a Spanish expedition led by Christopher Columbus was the first to cross the Atlantic to reach the West Indies in 1492.

AT L A S O F T H E O C E A N S

Isla

Ma gdalen a

428

7

Westerlies

60ºS

8

Beaufort Scale 0–3 3–5.5 over 5.5

90ºW

A

Speed 0–10 mph (0–16 km/h) 10–25 mph (16–40 km/h) over 25 mph (over 40 km/h)

Antarctic Circle

ANTARCTICA 60ºW B

C

D

E

F 0º

30ºW

B ay

t

L

l

Labr a dor ik Basin Eir

ab

Ima

s an n e Ch k j a k y ua rss Re

R

g id

e

Reykjavik Ice la n d Basin ge Rid k n an o t t lB Ha k al c o R

Plateau

a Sc

nd

in

Oslo Stockholm

North Sea

sea level

a avi

i c Sea

r ai St

Reykjanes Basin ne

N o rw e g i a n Basin Faeroe Islands

KEY

1

Norweg ian S e a Voring

Helsinki

60ºN

6,500 ft (2,000 m)

Riga

9,800 ft (3,000 m)

Dn

r

3,300 ft (1,000 m)

St Petersburg

N Dublin Britain Mi orth C h a r l i e- G i b b s F Hamburg O VGdansk d- w Ireland London r act ur e Zon e Oc es d istula Elb Dn es ter ea t A Amsterdam 4,139m e Celtic ieper n 13m t Ca lan (13,580ft) Porcupine Shelf 691m Gulf Newfoundland (43ft) e S ny tic n e i of S Plain (2,267ft) Odesa on tL Biscay Venice Grand Banks of aw Halifax y Rise ren Newfoundland a Plain Marseille be u D n c a 69m ce Bis Black Sea s– Iberian (226ft) e Barcelona r Naples Istanbul Plain Newfoundland zo Basin N Lisbon Athens Azores oe Seeaw E Ocean East sh ts m ng ograp Azores Fracture Zone rse oun ou c her o am Strait of Medite Sohm Algiers Tunis iF e Beirut Gibraltar r ranea t racture Zone Bermuda Plain n Sea Madeira Casablanca n 5,464m Madeira A tla Great Meteor Tripoli n ti s (17,927ft) Suez Canal Plain Canary Frac tu Tablemount Alexandria ud Islands r e Zo ne

do

800 ft (250 m)

Arctic Circle

1,600 ft (500 m)

B alt

Jan Mayen

429 90ºE

North Cape

Nuuk

ge Rid

I

60ºE

30ºE

it Stra ark m n De Iceland

L abrad or S ea ra

H

Greenland

Ba ffin Basin 218m Da (715ft) vis

Strait

G

er

i

16,400 ft (5,000 m)

2

land seamount

R

A

i

d g e

Rhin e

E U RO P E

sea depth

Ri s

e

SH

nd la ts n

maximum depth on map

a

t

e

ATLANTIC Nares P l ai n

Puerto TrenchRic

acud

4,700m Demerara Ve ma Fract ure Zone Gambia(15,421ft) Plain Plain D o l d r u m s Fr a c t u r e Z o n e

AFRICA

Conakry

4 Lagos

Monrovia Accra Sierra Leone Abidjan Douala Gulf of Basin Niger Guinea e n o Z ne ure Libreville Cear G u i n e a Fan Saint Paul Fract racture Zo aP F l ai on e n manche o o R Z z a e m B a s i n n r A tu Fernando de Chain Frac Belém Noronha Co e Fortaleza re Zon Pernambuco Congo ractu F Basin Ascension Ascension Island Fan Recife Luanda o e Zone r u t c B r a zil e Fra B a s in Bode Verd Salvador Saint A ngola Namibe 5,706m Helena B asin (18,721ft) Zone e r u t c Hotspur a Fra Saint Helen 5,042m Seamount Ilhas (16,543ft) Isla Martin Vaz Rio de Janeiro Trindade Walvis Bay

Georgetown Amazon Fan

OCEAN

arcti

Ant

e

g

id R

is lv Wa

e Z on e

Discovery Tablemounts

6

INDIAN OCEAN

Cape Town

Cape of Good Hope

nt s

R

ou e am Davis S

America–

Tropic of Capricorn

Orange

An

cti tar

idg ca R

n A t l a n t i c – I

e

d

i a

i d

g

n 7

Atlantic–Indian Basin Maud Rise

We d d e ll P la in

Antarctic Circle

Lazarev Sea

tr As

id

Rid

A N TA R C T I C A

30ºW

0º

E

SCALE

0

500

1,000

500

1,500

1,000

2,000

8

2,500 km

1,500

2,000

2,500 miles

60ºE

30ºE

F

60ºS

ge

0

lf e Ice She Ronn

30ºS

e

SOUTHERN OCEAN

South Orkney Islands

We d d e l l Sea

D

5,115m (16,782ft)

Tristan da Cunha

Islas 1,748m Or South (5,735ft) ca Georgia Sandw Sou das ich Ri s e

East Scotia Basin

Namibia Plain

C ape B asin

3,667m (12,031ft)

th rench T

Scotia Sea

e e Zo n Fr a c t u r

G

H

90ºE

I

AT L A S O F T H E O C E A N S

Cape Horn sage e Pas ands Drak Shetland Isl h t u o S sula nin e cP

tur G o u g h Fr a c

Z a p i o la R i d ge

land E scar pme nt Falkland Plateau

Ya ghan B as i n

ng o

R i g d e

1,739m (5,706ft)

Arg en t in e B as i n Fa l k

i d - A t l a M n t i c

Ur u

Rio G r an de

Rio Grande Rise

D e se r t

Porto Alegre

636m (2,087ft)

Montevideo

Falkland Islands

5

ib

Buenos Aires

Santos Plateau

ay gu

Equator

Nam

AMERICA

Francis c

SOUTH

Tocantins

Paramaribo Cayenne

Par a na

Sen Cape eg Verde Islands Dakar

Verde Basin

Sao

Caracas co O r i no

a Fr ac t ur e Zon e

S a h a r a

r

Lesser A

3,780m (12,402ft)

ge Ni

ntilles

o

B a rr

Tropic of Cancer

254m Cape Verde (833ft) Plain Cape Verde Terrace Cape

al

M i d - A

8,962m (29,404ft)

3

l

a

Be rm

30ºN

l Ni

Sargasso Sea

rk

St

i ra

t

Iceland Plateau

Norwegian Sea

nafl Akureyri

r Breidhafjördhu 2,460m (8,071ft)

Faxaflói

(10,073ft) 22m (72ft)

Th

á jórs

94m (308ft)

Heimaey Surtsey

e id

e ja k

1,690m (5,545ft)

659m (2,162ft)

AT L A N T I C O C E A N g

land

50

0

150

50

150

250 km

200

250

B

Hatton–Rockall Basin

C

straddles the Mid-Atlantic Ridge and is one of the few places on Earth where it is possible to walk on newly created oceanic crust. It is the site of sea floor spreading that was responsible for linking the Atlantic to the Arctic Ocean around 36 million years ago. The surrounding seas are areas of water and heat exchange between the two oceans.

300 miles (480 km) 180 miles (290 km)

Most of the water leaving the Arctic Ocean flows into the north Atlantic through the Denmark Strait, propelled by the East Greenland Current. Icebergs from the eastern side of the Greenland Ice Sheet are carried south by this cold current, while the warm North Atlantic Drift flows northeast on the eastern side of the island, between Iceland and the Faeroe Islands. At depth, cold, dense Arctic bottom water pools to the northeast

101m (331ft)

D

of Iceland until it overflows the Greenland–Iceland Rise and cascades 6,500 ft (2,000 m) down into the main Atlantic basin. This is the start of a global journey as the dense water circulates around the deepest parts of the world’s oceans—the deep-water leg of the “great ocean conveyor belt” (see p.61). In winter, sea ice builds up along the Greenland coast. Sometimes, cold winds blow east off the Greenland Ice Sheet, pushing sea ice offshore. More sea ice is created as the wind cools the exposed surface water, and a tongue of sea ice can extend south from the Greenland Sea through the Denmark Strait.

930 miles (1,500 km)

HEIGHT ABOVE SEA FLOOR RATE OF SPREAD 3/4

10˚W

E

Reykjanes Ridge LENGTH

Rockall

Rockall Bank

ATLANTIC OCEAN B3

THE ISLAND OF ICELAND

Denmark Strait

15˚W

20˚W

Iceland

ATLANTIC OCEAN B1

5m (16ft)

505m (1,660ft)

300 miles

25˚W

30˚W

A

200

Ha

0

100

tt

SCALE

tectonic plate boundary

AT L A S O F T H E O C E A N S

R on

sea depth maximum depth on map

6,500 ft (2,000 m)

in (1.8 cm) per year

The Reykjanes Ridge is the part of the Mid-Atlantic Ridge that rises up to the ocean surface to the southwest of Iceland. The ridge clearly displays the parallel ridges and valleys that are left behind on either side of the central rift as the sea floor spreads at a divergent plate boundary. Here, the North American and Eurasian plates are moving apart at 1/2–1 in (1–2 cm) per year. The parallel features

60˚N

S

George Bligh Bank

id

2,933m (9,623ft)

seamount

Rosemary Bank

e

3

dg e

l fCape h e W rath

Hebr id Outer Heb ea r id n es

e

Faeroe Bank 174m Bill Baileys (571ft) Bank W yville T Outer hom son Bailey Ri

Iceland Basin

n

R

68m (223ft)

Fa er o

p

16,400 ft (5,000 m)

y

Tórshavn

Ga

60˚N

9,800 ft (3,000 m)

MINIMUM WIDTH

Faeroe Shelf

e

3,300 ft (1,000 m)

LENGTH

Ri dg e

s

1,600 ft (500 m)

4

2

R

800 ft (250 m)

65˚N

3,300m (10,827t)

FAEROE ISLANDS

g

sea level

6,500 ft (2,000 m)

1

251m

er (824ft) oe –Ic el an d

KEY

3

ircle

Arctic C

ICELAND

Reykjavik Keflavik

Fa

Re y k j an es Ba s i n 3,070m

5˚W

Hu

en

57m (187ft)

D

Serm Vall ilik ey

10˚W

15˚W

19m (46ft)

m

a

Ammassalik 65˚N

2

20˚W

F

Fae roe – Tro Shet ugh lan d

Greenland–Iceland Rise

E

A Vi egir ki ng Ridge Tr ou gh

25˚W

30˚W

35˚W

D

Circle

G REEN LAND 1

C

ói

Arctic

B

Kolbei nsey Ridge

A

430

Stornoway

UNITED KINGDOM F

become less distinct away from the ridge, as the older crust is draped in sediment in the Reykjanes Basin and Iceland Basin. Before this rifting started, Greenland and Britain were almost adjacent, connected by a land bridge. The Hebrides and Faeroe Islands, Rockall, and the other banks on the eastern side of the Iceland Basin are the result of basalt floods associated with the early stages of the rift. SURTSEY

Surtsey was born in 1963 when a volcano on the western flank of the Mid-Atlantic Ridge breached the surface of the sea off Iceland.

4

THE WESTERN NORTH ATLANTIC

The Western North Atlantic

ATLANTIC OCEAN B3

ATLANTIC OCEAN E2

Grand Banks

Gulf of Maine AREA

35,000 square miles (90,700 square km)

MAXIMUM DEPTH

AREA

1,240 ft (377 m)

warm, fast-flowing INFLOWS Atlantic Ocean; St. John, Penobscott rivers Gulf Stream pulls away from the North American coast and runs Like much of the continental shelf off northeastward as the North Atlantic Drift. The Labrador Current the east coast of North America, the brings cold water south along the coast as far as the Gulf of Maine. Gulf of Maine was above sea level

Gulf of St. Lawrence 60,000 square miles (155,000 square km)

AREA

MAXIMUM DEPTH INFLOWS

7,550 ft (2,300 m)

Atlantic Ocean, St. Lawrence River

The gulf lies between the mouth of the St. Lawrence River and the islands of Newfoundland and Cape Breton. The Laurentian Trough, between the two islands, was scoured out by the Laurentide Ice Sheet during the last ice age. It channels sediment from the river over the edge of the continental shelf and onto the Laurentian Fan. The St. Lawrence River is the largest A

SEA ICE IN THE GULF OF ST. LAWRENCE

B

D

E

60˚W

70˚W

50˚W

Isl

e

Île d’Anticosti Hongued oP ass Gulf of age St. Lawrence Péninsule de Gaspé Rocher Percé

NANTUCKET ISLAND

it tra tS bo Ca

nce wre La . t S

Ottawa

Saint John

Toronto

Huds on

Del aware

anna

New York Baltimore

v No

a S

Halifax

Chesapeake Norfolk Bay

En

gl

an

d

Se

5,464m (17,927ft)

Hatteras Plain

am

0

60˚W

B

wf

40˚N

ou

nd

lan

d R id

200

100

C

0

100

5,356m (17,573ft)

300

400

4

500 km

200

300

400

500 miles

50˚W

D

3

ge

SCALE

Nashville Seamount

70˚W

A

Newfoundland Basin

s

sR ra

w

nt

tte Ha

e idg

3,883m (12,740ft)

AT L A N T I C OCEAN ou

Cape Hatteras Cape Lookout

63m (207ft)

6,492m (21,300ft)

Ne

2

Newfoundland Seamounts

Ne

903m (2,963ft)

1

Milne Seamounts

(226ft)

Washington Delaware Bay

4

Sable Island

Emerald Cape Sable Basin Browns Georges Bank 69m

Cape 3m Basin Cod (10ft) Martha’s Nantucket Georges Bank Long Vineyard Island Island

Providence

Fu

50˚N

E

F

AT L A S O F T H E O C E A N S

ac tom

3

Sus q

ueh

40˚N Po

Boston

Gulf of Maine Murray Basin

of

Cape Breton Island

a coti

Rise

ce est an A C a t l an ny tic on

126m (413ft)

Cape Race Grand Banks of Newfoundland

n ntia u r e an F

U N I T ED STATES O F A M ER IC A

Conn e

Buffalo

Portland

y nd

13m (43ft)

La

cticu t

Lake Ontari o

n tia en ur gh LaTrou

Montréal

St. Lawrence Seaway

West 2,273m (7,458ft) Thulean

Flemish Cap

St. John’s

ST. PIERRE AND (1,529ft) MIQUELON

Ba y

2

Newfoundland

Îles de la Cape Madeleine Prince Edward North 466m Island

Québec

Orphan Knoll

St

309m (1,014ft)

Placentia Ba y

50˚N

O

ll Belle Isle Be Cape Bauld of Grey Islands it ra ite h e Bay WBay Dam tre Fogo Island o N

CANADA

40˚W

3,826m (12,553ft)

w rth No id– M

1

F

119m (390ft)

e

80˚W

C

330 ft (100 m)

The Grand Banks is a large area of continental shelf, extending up to 310 miles (500 km) off Newfoundland. The area is renowned for dense sea fogs, which arise when warm, moist air from the south is chilled by the cold Labrador Current, causing condensation. The Labrador Current presents another shipping hazard by bringing icebergs to the area—the Titanic famously sank south of the Grand Banks in 1912. Although turbidity currents have never been directly observed, their power was felt in 1929 when an earthquake triggered a huge sediment flow (submarine landslide) down the continental slope off the Grand Banks. Submarine telegraph and telephone cables were broken over a distance of 500 miles (800 km)—from the timing of the breaks, the speed of the flow was estimated at 25–34 mph (40–55 km/h).

during the last ice age. Georges Bank stands 330 ft (100 m) above the floor of the Gulf, and was an island until 6,000 years ago. Cape Cod and the islands of Nantucket and Martha’s Vineyard are the highest standing of a series of moraines left behind as the glaciers retreated and the sea level rose. Occasionally, the Gulf Stream lies not far offshore and the temperature of the sea off Nantucket beaches can be several degrees higher than it is off nearby Cape Cod. North of the Gulf of Maine, the Bay of Fundy extends more than 120 miles (200 km) inland. The bay acts like a funnel, producing a tidal range of 43 ft (13 m) at its northern end, which is the highest in the world.

freshwater input to the Atlantic from the North American east coast, and its mouth is the largest estuary of its type in the world. The St. Lawrence Seaway, which was opened in 1959, gives vital shipping access to the Great Lakes.

108,000 square miles (280,000 square km)

AVERAGE DEPTH

IN THE WESTERN NORTH ATLANTIC, the

ATLANTIC OCEAN C2

431

432

A

THE ATLANTIC OCEAN

The North Sea and Baltic Sea

B Arct

20˚W

C 10˚W

ic Cir

cle

1

northwest coast of Europe, the largest of which is the North Sea. The North Atlantic Drift brings warmer water into the region, producing the mild climate enjoyed by adjacent coastal areas.

nd

Iceland Basin

3

Fa FAEROE Tórshavn e ISLANDS

60˚N

Faeroe Bill Baileys Bank Bank Wy vill eT ho m so

220,000 square miles (570,000 square km)

MAXIMUM DEPTH

2,300 ft (700 m)

INFLOWS North Atlantic; Elbe, Weser, Ems, Rhine, Scheldt, Thames, Humber rivers

Water from the Atlantic enters the North Sea between the Shetland and Orkney Islands, flowing south down the Scottish and English coasts. Warmer Atlantic water also enters from the English Channel and flows east along the Dutch coast, resulting in a counterclockwise circulation. The largest sand banks on the North Sea floor, including the Dogger, Jutland,

u

d lan

Tr

ou

eb

H

h Inverness

Glasgow rt

Donegal Bay

Edinburgh

Belfast Isle of Man

Galway Bay

Irish Sea

IRELAND

pi ne

Ba n

No

Malin Head

k

Liverpool

Dublin

Ch ann el

Sh

Po rcu

Anglesey

Cork 7

. St

Celtic Sea

Severn

UNITED

KINGDOM

Isles of Scilly

99m (325ft)

Southampton

Land’s End

Isle of Wight

English Channel Cherbourg Channel Islands Golfe de St-Malo

10˚W

OIL RIG IN THE NORTH SEA

A

Thames

Plymouth

38m (125ft)

Celtic Shelf

Cardigan Bay

Cardiff Br istol Chann el

50˚N

8

Moray Firth

s

30m (98ft)

gh

90m (295ft)

Goban Spur

Orkney Islands Cape Kirkwall Wrath

Stornoway c in eM h T Isle of Skye

G eo rg e’s

AT L A S O F T H E O C E A N S

AREA

f

el ann

2,932m (9,620ft)

6

el

Sh

Ch

Ire

ro

Hebrides Seamount

d

h

North Sea

ka

T ll

gh

n la

Inner He br ide

c Ro

The 10-mile- (16-km-) long Oresund Bridge links the Danish capital Copenhagen with Malmo in Sweden.

and Fisher banks, are terminal moraines marking the southern edge of the ice sheet during the last ice age, when the bottom of the sea was exposed by lower sea levels. A trough located to the west of the Norwegian Trench is buried under thick sediments that contain oil and gas deposits.

Rockall

5

ACROSS THE ORESUND STRAIT

ATLANTIC OCEAN D6

ll

k

de

an

et

53m (174ft)

d

He br

Ro

a ck

n Ba

ri

5m (13ft)

n

The Baltic is a shallow, virtually enclosed inland sea with little tide. It does not benefit from the warmth of the North Atlantic Drift, and its northern branches, the Gulf of Bothnia and the Gulf of Finland, ice over in the

10m (33ft)

no

Vistula, Oder, Western Divina rivers

winter. A large influx of river water gives the Baltic a low salinity—it is the largest area of brackish water in the world. Its only outflow is to the North Sea via the Danish Straits (three channels linking the Baltic to the Kattegat), Kattegat Bay, and the Skagerrak Strait. There is a weak influx of dense salt water at depth that isolates the basin floor from the surface waters, producing an oxygen-depleted dead zone. Without significant out- flows, the Baltic Sea is vulnerable to pollution carried in by rivers and from large population centers on its coasts. Although there is a sea route to the North Sea, there is also a shorter, more sheltered route through the Kiel Canal.

Ri

Rosemary Bank

an

INFLOWS

1,473 ft (449 m)

4

n

ge

149,000 square miles (386,000 square km)

MAXIMUM DEPTH

George Bligh Bank

Fa er oe –S h

p

AREA

68m (223ft)

Ga

174m (871ft) Outer Bailey

Fjords cut into the Atlantic coast of Norway, showing where ice-age glaciers scoured deep valleys below today’s sea level.

Baltic Sea

dg e Faeroe Shelf

PULPIT ROCK AT LYSEFJORD

ATLANTIC OCEAN G5

Ri

e ro

The Norwegian Sea lies between Norway and Iceland, separated from the main part of the north Atlantic by the submarine Faeroe–Iceland Ridge. Although situated at high latitude, this sea is kept free of ice by the warm, salty North Atlantic Drift, which flows from the southwest between Scotland and Iceland and continues into the Barents

3,300m (10,827ft)

a

13,020 ft (3,970 m)

Central North Atlantic, numerous Norwegian fjords INFLOWS

231m (824ft)

ides

534,000 square miles (1.4 million square km)

MAXIMUM DEPTH

2

el Ic e–

AREA

i ir R h Aeg ug ro T g Vikin

94m (308ft)

o er Fa

Norwegian Sea

Sea (see p.427) as the Norwegian Atlantic Current. This relatively warm water is the reason for the Norwegian port of Bergen’s reputation as the wettest place in Europe, with rain expected at least 275 days a year.

ICELAND

Outer

ATLANTIC OCEAN D1

dg e

a number of shallow seas cover the continental shelf off the

B

C

D

E

F

0˚

G

10˚E

Vo rin g P la tea u

Tr ae na

1,280m (4,200ft)

Ve s tf jo

Norwegian Basin

Røst Bank

H

I

20˚E

en rd

30˚E

SCALE 0

Bodø

KEY 100

50

150

200

250 km

sea level

1 De ep

0

50

150

100

800 ft (250 m)

250 miles

200

Arctic Circle

N o r we g i an Sea

1,600 ft (500 m)

Traena Bank

3,300 ft (1,000 m) 6,500 ft (2,000 m) 9,800 ft (3,000 m)

Luleå Oulu

222m (738ft) 85m (279ft)

Sklinna Bank

16,400 ft (5,000 m)

Halten Bank

2

of B oth nia

SWEDEN land

Umeå

Trondheimsfjorden Frøya Bank Hitra 94m (308ft)

1,320m (4,331ft)

433

Trondheim

Vaasa

FINLAND

sea depth maximum depth on map tectonic plate boundary

Gulf

gh ou r T

seamount

3

N we

Fair Isle

Helsingborg

Ventspils

Weser

Bal tic S e a Courland Lagoon

Malmo

West ern

Gulf of Danzig

5

LITHUANIA Klaipeda

RUSSIAN FEDERATION

Kaliningrad

POLAND

6

BELARUS

Oder

Elb

L AT V I A Riga

e

7

Mittelandkanal

Amsterdam Rotterdam

London

ov er

M

of D

a as

Dover

Calais

Elb

e

Antwerp

GERMANY

B EL GI U M

ine

Me u

Rh

ait Str

se

os e

l

M ain

Le Havre

FRANCE

Se

M LUXEMBOURG

50˚N

CZECH REPUBLIC

ine

0˚

STRAIT OF DOVER

The Strait of Dover is one of the world’s busiest shipping lanes, linking the English Channel to the North Sea and giving shipping access to Europe’s ports. It also provides ferry links between Britain and the European mainland, although much of this traffic now uses the Channel Tunnel. 20˚E

10˚E

D

E

F

G

H

I

8

AT L A S O F T H E O C E A N S

Ems

NETHERLANDS

Bremen

Gulf of Riga

Liepaja

Gdansk

4

E STO N I A

ma n Ne

Vlieland Friesia Bank

ands n Isl

Lake Peipus

Öland 9m (30ft)

Bornholm Lolland Falster Bay Kiel rg bu Rugen Pomeranian Bay Kiel Bay len k ec M Kiel Rugen Canal Hamburg Szczecin

Helgoland Bay

Well Bank

Tallinn

ina Dv

Århus J y l l a nd

Weiss Bank

15m (49ft)

Kalmar

Halmstad

Karlskrona

DE N M AR K Copenhagen Odense Sjaelland Fyn

Dogger Bank

ash eW h T

Laeso Aalborg

gat

13m (43ft)

Saaremaa

Gotland

Gothenburg

RUSSIAN FEDERATION

and

Lake Pskov

tte

Jutland Bank

ag

er

Hiiumaa

Vättern

rak

Ka

Great Fisher Bank

Sk

N or t h Se a

Trent

700m (2,279ft)

Lindesnes

Gotland Basin

Norrköping

Vänern

Kristiansand 67m (200ft)

Kingston upon Hull

175m (574ft)

Stockholm

South Bank

Barmade Bank

lf

inl of F

Oslo

rden Boknafjo Stavanger

Devil’s 75m Hole (246ft)

Åland

Gu

Hardangerfjorden Walker Bank

60˚N

St Petersburg

Helsinki

Bergen

e n ch

Lerwick

Gävle

n Tr

Viking Bank

Turku (Åbo)

N O R W AY

gia

Shetland Islands

a Glåm

or Sognefjorden

MIDDELGRUNDEN WIND FARM

Arranged in an elegant curve 1.2 miles (2 km) east of Copenhagen, Denmark, each of this wind farm’s 20 turbines can produce 2 megawatts of electricity.

435

Wind-farming in the Baltic OFFSHORE WIND FARMS

UNDER CONSTRUCTION

Declining oil stocks, threats to fuel supplies, and the risks of climate change are increasingly focusing attention on alternative sources of energy that do not generate greenhouse gases. After hydroelectricity, wind-farming is the most advanced source of renewable energy. It is easiest to build wind farms on land, but many people do not want turbines built near their homes.Wind farms built at sea are less controversial, although costlier to build and maintain. Since it is usually windier at sea and there are no hills or trees to cause turbulence, offshore turbines are more efficient than land-based ones. The world’s first commercial offshore wind farm was built in the Baltic (see below). Other large wind farms are in place or under construction in the nearby Kattegat sea area; in British, German, Danish, Dutch, and Belgian areas of the North Sea; and off the coast of China.There are also wind farms in the Mediterranean and off Ireland, Japan, Norway, and Spain, while a large farm is planned in South Korea.The US and Canada also have various proposed offshore projects for the Pacific Coast, East Coast, and Great Lakes. Because they burn no fossil fuels, wind farms can help reduce greenhouse gases. However, the overall benefits may take some time to appear. It can take 1,000 tons of concrete just to build the foundations of an offshore turbine, and concrete production is one of the biggest sources of greenhouse gases.

MASSIVE BLADES Wind-turbine blades are assembled on the dockside, then carried to the tower on a barge. The rotors reach 295 ft (95 m) in diameter. FOUNDATIONS The concrete foundations of a turbine are cast onshore in a dry dock. They are then floated out to sea and sunk in shallow water on site.

wind farms under construction

wind farms

N O R W AY SWEDEN

North Sea Kattegat

Middelgrunden

DENMARK Vindeby

Baltic Sea

LARGEST BALTIC WIND FARM

The countries around the Baltic Sea and the neighboring Kattegat sea area have played a central role in the development of offshore wind energy. The world’s first commercial offshore wind farm was commissioned in 1991 near the Danish fishing port of Vindeby. The Baltic and Kattegat are ideal for windfarming because of their low average depths. The first wind farms in this region were sited in water less than 33 ft (10 m) deep.

POWER DISTRIBUTION

Baltic and Kattegat Wind Farms

POLAND GERMANY

CASUALTIES

Rodsand ll

SUBSTATION The electricity generated by offshore turbines has to be transmitted to land. This substation collects power from 72 turbines at the Nysted Offshore Wind Farm off southern Denmark, and transforms it from 33,000 to 132,000 volts for transmission ashore via 30 miles (48 km) of submarine cable. RODSAND II Completed in 2010 and costing 450 million Euros, Denmark’s Rodsand II is the largest wind farm in the Baltic and also one of the world’s twelve largest offshore farms. An average of 6 miles (9 km) from shore, it has 90 turbines, arranged in five arcs. Rodsand II has a peak capacity of 207 megawatts and is saving the emission of around 700,000 tons of CO2 per year.

WHITE-TAILED EAGLE Although wind energy may bring about potentially huge benefits for wildlife by reducing climate change, turbines do sometimes harm birds. Four dead white-tailed eagles were found at an offshore Norwegian wind farm in early 2006.

B

50˚N

40˚W

C

D

Charl ie

20˚W

Fracture

ll Fr acture

4,139m (13,580ft)

2,500m (8,203ft)

Olympus Knoll

Milne Seamounts

458m (1,503ft)

g

e

Altair Seamount

102m (335ft)

Ki ng sT Antialtair rou

i d

3,883m (12,740ft)

R

Ak a

6,324m (20,749ft)

dem ik K urc h at ov Frac ture Zon Corvo e

e or Az

e

2,160m (7,087ft)

i

Oc

e an og rap

Ha y

São Jorge Faial

es

tu r e

Terceira Rift

A z o r e s P l a Pico A z o r e s teau São Miguel

-

Ponta 117m Delgada (384ft) Santa Maria

M he r

772m (2,533ft)

Fra c

d

Graciosa Terceira

Fra ctu re

Zon

5,143m (16,874ft)

racture Zone E a s t A zo r e s F

e 275m (902ft)

Zon e 2,194m (7,199ft)

AT L A S O F T H E O C E A N S

5,485m (17,996ft)

7

At lan

8

tis

0

50

a

Great Meteor Tablemount

La Palma

SCALE 0

Madeira

Madeira Plain

238m (781ft)

Fra ctur e Zo ne

Funchal

ir de Ma

Cruiser Tablemount

30˚N

Ri d

ge

6

Flores

l

Zo n

A

5

Frac ture

t

Pico

a

n

t

i

4

O C EA N

gh

c

AT L A N T I C

Seamount

s– Bi s

Newfoundland Basin 40˚N

4,885m (16,028ft)

Z o ne

691m (2,267ft)

3

n

i

Fracture Zone

Ma xw e

Newfoundland Seamounts

2,193m (7,195ft)

a Pl

East Thulean Rise

713m (2,339ft)

4,579m (15,024ft)

126m (413ft)

2

Zone

e pin

Fara day

691m (2,267ft)

rcu Po

ic nt n tla yo t A an es C w an th ce or O N idM

Flemish Cap

F

30˚W

Gibbs

Hecate Seamount

1

E

Ri se

A

ca y

436

100

50

150 250 300 km

100

150

250

Canary Basin

300 miles

4,645m (15,404ft)

Hierro 20˚W

30˚W

40˚W

A

B

C

Gomera

D

E

F

G

H IRELAND

Ban ine Po r k Se cupin e a bi ght

10˚W

I

UNITED

Porc u

p

Cork

Celtic 38m (125ft)

lish Eng

Isles of Land’s Scilly End

Biscay Plain

C

50˚N

Se i n e

1

Brest

FRANCE

re Pointe Loi du Raz Belle Île Nantes Pla tea ud eR Île de Ré oc Île d’Oléron he bo nn e Bay of Bordeaux

Biarritz Cabo de Ajo Costa Verde Santander Donostia– San Sebastián Gijón

Cabo Ortegal

2

3

n ia er Ib

SPAIN

40˚N

The Old Lighthouse at La Raz Cap is one of several that mark treacherous rocks off the Brittany Peninsula in the Bay of Biscay. 4

n ai Pl

Tagus

ATLANTIC OCEAN D5

Gua

dian

Cabo de Roca Cabo Espichel Cabo de Sines

G

Ri d

e oe ing Gorr sh nts e Gettysburg r s ou Hoeam Seamount S

ir uiv alq uad

Algarve

Cabo de São Vicente

Gulf of Cadiz Strait of Gibraltar

Gibraltar Mediterranean

Sea

Ceuta Tangiers

Ampere Seamount

Rabat Seine Plain

Seine Seamount

800 ft (250 m) 1,600 ft (500 m)

Agadir

7

Co nc Ba ept nk io

16,400 ft (5,000 m)

seamount sea depth maximum depth on map

Cap Juby

tectonic plate boundary

Las Palmas

WESTERN SAHARA 10˚W

G

H

I

TYPE

Volcanic islands

AREA

2,900 square miles (7,400 square km)

NUMBER OF ISLANDS

land

Fuerteventura

ATLANTIC OCEAN G8

8

7

The name of these islands derives not from the yellow bird of the same name, but from the Latin word for dogs, Canaria. The islands are volcanic, overlying a mantle hotspot. Pico del Teide on Tenerife is the third largest volcano on Earth, rising more than 12,000 ft (3,700 m) above sea level, or almost 23,000 ft (7,000 m) from the sea floor. It

The islands rise from the extensive Azores Plateau, an area of thickened ocean crust. Although volcanic in origin, the oldest islands also include substantial accumulations of limestone and clay sediments. A mantle hotspot (see p.51) underlies the plateau and seems to be slowly spreading it apart at the Terceira Rift, a fracture that links the East Azores Fracture Zone to the Mid-Atlantic Ridge. The last volcanic eruption in the Azores was in 1957, when the Capelinhos volcano produced a cinder island (an island composed of lava fractures called cinders) off Faial’s coast. last erupted in 1909. Teide’s slopes are unstable, and there is evidence that huge landslides have occurred in the past. There is also a risk that volcanic activity or earth tremors could cause part of La Palma island to slip into the sea, resulting in an enormous tsunami. Such an event would threaten the coasts of the north Atlantic, including heavily populated parts of North America, with inundation. The islands’ first volcanic eruptions in 40 years occurred in 2011, under the sea off El Hierro, the youngest and most southwesterly of the islands. TENERIFE ISLAND

AT L A S O F T H E O C E A N S

3,300 ft (1,000 m) 6,500 ft (2,000 m) 9,800 ft (3,000 m)

MOROCCO

Lanzarote

9

The Mid-Atlantic Ridge is the dominant seafloor feature in the eastern Atlantic region, with a central trough and numerous transform fracture zones. Just east of the ridge, the Azores island group straddles the triple junction between the Eurasian, African, and North American plates.

Canary Islands

sea level

Safi

Canary Islands

890 square miles (2,300 square km)

6

Casablanca

C an yon Cap Rhir n

Volcanic islands

AREA

KEY

4,265m (13,993ft)

Ag ad ir

TYPE

NUMBER OF ISLANDS

5

ge

Tagus Plain

Azores

a

Lisbon

Santa Cruz Tenerife

The Bay of Biscay lies between Brest, on the Brittany Peninsula, and the north coast of Spain. The northern half of the bay is quite shallow, overlying the continental shelf, but this steeply drops away to the Biscay Plain, which is a small, partially opened ocean basin. Ships crossing the bay experience heavy seas, as

PORTUGAL 5,536m (18,164ft)

Dacia Seamount

15,535 ft (4,735 m)

Loire, Dordogne, Garonne, Adour rivers

full-size Atlantic rollers are amplified by the sudden shallow depth. There is a weak counterclockwise surface current within the bay. The Charcot Seamounts, Azores–Biscay Rise, and Kings Trough mark an inactive crustal fracture where the sea floor was once splitting apart.

LIGHTHOUSE ON THE BAY

uro

Cabo Mondego

20m (66ft)

86,000 square miles (223,000 square km)

INFLOWS

Do

Oporto

Bay of Biscay MAXIMUM DEPTH

La Coruña Vigo

THE EASTERN NORTH ATLANTIC

AREA

Cabo Fisterra

492m Galicia (1,614ft) Bank

The East Atlantic is renowned for its winter

ATLANTIC OCEAN I3

Biscay

4,870m (15,978ft)

437

storms, which batter the western coasts of Europe. The energy for these storms is provided by the Gulf Stream feeding warm water into the North Atlantic Drift, which flows to the northeast. The North Atlantic Gyre pulls some of this water south along the African coast as the Canaries Current.

Channel Cherbourg Islands Golfe de St-Malo

99m (325ft)

ts oun Seam t o c r a Ch p Ga eta h T

0˚

annel KINGDOM tol Ch Br is Isle of Wight Sea Plymouth hannel

Celtic Shelf

Goban Spur

THE EAST ATLANTIC

A

438

B

C

D

E

0˚

F

10˚E LIEC H TENSTEIN

AU ST R I A

SWITZE R LAN D

S LOV ENIA

1

Trieste

Venice Adige

2

ROCK OF GIBRALTAR r n o

The port of Gibraltar is situated on a narrow peninsula near the Mediterranean’s exit to the Atlantic. It is an important naval base, controlled by Britain since Spain ceded sovereignty in 1713.

Eb 40˚N Fa

a Cost

h ug Tro a ci en

Rhône Fan 1,830m (6,004ft)

Corsica

d’Elba

Ajaccio

Balearic Basin

Cagliari

PORTUGAL

Alicante

Alboran Sea

ATLAN TIC O CE AN

B

Cabo de Gata Cap Ferrat

Tanger Ceuta

Algiers

Naples Salerno

Seamount

Ty rr he nia n Ba sin

Marsili Seamount

Strait of Messina Messina

2,860m Cap Blanc (9,384ft)

1,740m (5,709ft)

C

Malaga Costa del Sol

Strait of Gibraltar Gibraltar

3

Cartagena a Cabo de Palos ost nca a Bl

S PA I N

VATICAN CITY

Rome

Tyr r h e n i a n S e a Vavilov

Sardinia

a

Minorca l Golfo de VaM Palma Valencia Ch allo Majorca s an r c Valencia n Basin nd Ibiza el la Algerian Basin s I Cabo de Formentera i c r a La Nao ale

re

Barcelona

va Bra

ve Te

ANDORRA

g rsica Trou h S Sar ardinia–Co Terrdinia ace

Sète

Gulf of Po Rijeka Venice Genoa A dr Gulf of SAN MARINO Nice Genoa i a Dalm Livorno Marseille r MONACO a ti u Ancona z c S tia d’A Ligurian Sea e t I T A LY ô ea Toulon C Isole Pescara

Rhône

FRANCE

Béjaïa

Annaba

Oran

Str Palermo ait of Sicily Catania Sic Ge la B il y Bizerte Cap as Siracusa Bon in Tunis M Malta alta Ma Halk El Tr lta Plateau Menzel Bank ou C Sousse gh han nel TUNISIA MALTA

Melilla

Sfax Gabès

Golfe de Tunisia n Gabès Pla t e a u

MOROCCO ALGERIA

Medina Bank Melita Bank 104m (341ft)

Tripoli

SCALE

4

0

200

100

300

400

500 km

L I B YA 0

100

200

300

400

500 miles

30˚N

0˚

A

B

C

The Mediterranean Sea and Black Sea THE MEDITERRANEAN IS AN ALMOST

enclosed sea, with high evaporation and salinity, a very small tidal range, and a complex floor. The adjacent Black Sea is the last remnants of the Tethys Ocean, which closed as Africa converged with Eurasia.

AT L A S O F T H E O C E A N S

ATLANTIC OCEAN D2

Western Mediterranean AREA

328,000 square miles (850,000 square km)

MAXIMUM DEPTH INFLOWS

11,800 ft (3,600 m)

Atlantic Ocean; Ebro, Rhône rivers

The entire Mediterranean loses three times more water by evaporation than it gains from rainfall and rivers combined. This loss is balanced by a surface inflow from the Atlantic through the Strait of Gibraltar. The inflow continues as an eastward current along the north African coast, giving rise to a counterclockwise circulation

in the western Mediterranean. At depth there is a strong undercurrent of outflowing salty water. The flat floors of the Algerian and Balearic basins are underlain by deep sediments. In contrast, the Tyrrhenian Sea contains many seamounts and ridges. A chain of active volcanoes (including Etna, Stromboli, and Vesuvius) is found on the sea’s eastern margin, where the African Plate is subducting beneath the Eurasian Plate. The eastward flow of surface water continues through the Strait of Sicily into the eastern Mediterranean. The narrower Strait of Messina, between Sicily and mainland Italy, is notorious for its whirlpool, possibly the inspiration for the Greek mythological sea monster Charybdis.

10˚E

D

ATLANTIC OCEAN H3

Eastern Mediterranean AREA

637,000 square miles (1.65 million square km)

MAXIMUM DEPTH INFLOWS

16,720 ft (5,095 m)

Black Sea; Adige, Nile, Po rivers

The eastern and western parts of the Mediterranean are separated by Sicily and the submerged Malta and Tunisian plateaus. The eastward flow from the western Mediterranean continues along the African coast, and a counter-clockwise circulation prevails in the eastern Mediterranean, and in the Ionian, Aegean, and Adriatic seas. Surface water becomes more saline through evaporation as it travels east,

E

and starts to sink after cooling by winter winds. It then returns westward, exiting through the Strait of Gibraltar about 150 years after entering. The sea floor is dominated by the Mediterranean Ridge, a result of compression between the convergent African and Eurasian plates. These sediments are older—70 million years compared with 25 million years in the western Mediterranean. The Adriatic Sea is a shallow branch of the eastern Mediterranean. Rising sea levels at the end of the last ice age flooded valleys parallel to its eastern shore, giving rise to the islands of the Dalmatian coastline. VENICE LAGOON

Venice was built in the shallow waters of a lagoon in the Adriatic. Its merchants grew rich by controlling access to the Silk Route.

F

G

H

I

J

20˚E

Danube

30˚E MOLDOVA Dn iest

Prut

HU N G A RY Drava

ROMANIA

CROATIA BOSNIA AND HERZEGOVINA

SERBIA AND MONTENEGRO

Varna

2,155m (7,070ft)

MACEDONIA

Salonica Chalkidiki

Ot

to ra n

ian

n ia u a

Ion Isl

Pátra

an

Cyclades

de Sea of Crete

ic Tr ou g

Trough

Irákleio

Crete

Sinop

h

se

Ordu

Trabzon

land

2

seamount

maximum depth on map

Basin Karpathos Anaximander Ridge

Tubruq

R id

ge

Gulf of Salûm

Lev

an

ti

ne

Ba

si

n

Mersin Iskenderun

Antalya Basin

ugh Latakia Cilicia Tro

CYPRUS

Limassol

Hefa Nil

ISRAEL

e Fan

Tel Aviv–Yafo Gaza

Nile Delta

H

ATLANTIC OCEAN H2

Aegean Sea 83,000 square miles (214,000 square km) 10,800 ft (3,294 m)

Black Sea, Mediterranean Sea

VOLCANIC ISLANDS

Canal

N

I

SKIATHOS ISLAND

Aegean islands consist mostly of hard metamorphic and volcanic rocks, so their coasts often show steep cliffs, headlands, and wave-cut features.

4

JOR DA N

J

the Aegean microplate. The Aegean Volcanic Arc stretches from Greece to Turkey through the southern Cyclades. These volcanoes are dormant or extinct, but earthquakes still occur at a depth of 95–105 miles (150–170 km). The islands of Santorini, in the southern Cyclades, are the remains of an explosive volcanic eruption around 1640 bc. This was the largest volcanic event of the last 10,000 years and may have caused the downfall of Crete’s Minoan civilization. Behind the volcanic arc, the main Cyclades sit on top of a subsided plateau. At the northern end of the Aegean, a transform fault marks the contact with the Eurasian Plate, an area prone to strong, shallow earthquakes.

The islands of Santorini in the Aegean Sea are the remains of an explosive volcanic eruption about 3,500 years ago.

Dead Sea

K

L

ATLANTIC OCEAN J2

Black Sea AREA

163,000 square miles (422,000 square km)

MAXIMUM DEPTH

7,200 ft (2,200 m)

Mediterranean Sea, Sea of Azov; Danube, Dniester, Dnieper, Kizil Irmak rivers INFLOWS

The Black Sea is an enclosed inland sea, connected to the Mediterranean Sea via the Dardanelles, the Sea of Marmara, and the Bosporus. There is negligible exchange of water with the Mediterranean, and the surface waters of the Black Sea are about half as saline as the eastern Mediterranean. A previous small outflow through the Bosporus to the Aegean appears to have been reversed due to reduced inflow after the damming of some of the rivers feeding the Black Sea. Although the surface waters are relatively fresh, below about 330– 490 ft (100–150 m) lies a highly saline water body with very slow turnover. Decaying organic matter consumes all the oxygen in this water, making the Black Sea the world’s largest oxygenfree marine system—the deep water is essentially dead. The basin is an isolated

BLACK SEA SHIPPING

The Bosporus, the narrowest strait open to international navigation, connects the Black Sea with the Sea of Marmara.

remnant of the north shore of the ancient Tethys Ocean. The southern part of the Black Sea is deep, but it is not as deep as the Mediterranean, and the underlying crust is thicker than most ocean crust. The northern parts—the Sea of Azov and the Gulf of Odessa—overlie a shallow continental shelf. The delta of the Danube, Europe’s longest river, extends from the western shore, and Danube waters have carried sediment across the edge of the shelf to build up a thick cone of sediment.

AT L A S O F T H E O C E A N S

The Aegean Sea contains more than 1,000 islands and is the source of most of the Mediterranean’s cold, saline deep water. Before 1990 this source was in the Adriatic, but climate changes have led to increased winter cooling in the Aegean. It is a geologically complex area, as the Aegean microplate and the Anatolian Plate to the east are caught between the converging African and Eurasian plates. The Aegean crust is of continental thickness, but has been stretched and thinned, notably in the area of the Cretan Trough, so that much of it is now below sea level. The Hellenic Trough and Pliny Trench mark where the African Plate is subducting beneath

30˚E

i le

EGYPT

20˚E

3

Tripoli tus Basin 633m us o do (2,077ft) C y p r i n Beirut Her s Eratosthenes Ba Tablemount LEBANON

Port Said Suez

INFLOWS

16,400 ft (5,000 m)

sea depth

Gulf of Antalya

Rhodes Rhodes

Surt

MAXIMUM DEPTH

3,300 ft (1,000 m) 6,500 ft (2,000 m) 9,800 ft (3,000 m)

Eas t Esc Black Sea arpm ent

Samsun

Antalya

ne

Alexandria

AREA

1,600 ft (500 m)

P l ain

1,695m (5,561ft)

1

tectonic plate boundary

4,335m Ptole my (14,223ft) Seam ounts nch ench Tre Pliny abo Tr r t S

1,269m (4,163ft) M ed i t e r r an Herodotus Trough ean He rod otus Darnah Ris e

G

800 ft (250 m)

Esc uca arp su me s nt

TURKEY

ca

Cretan

Benghazi

RUSSIAN FEDERATION

40˚N

Do

ds

Gulf of Sir te

sea level

Izmir

Mediter ranean Sea Herodotus S i r t e Seamount Rise

KEY

33m (108ft)

Mirtoo Pelagos ell en

Tag

40˚E

Novorossiysk Kerch Strait Ca

Sea of Marmara

Dardanelles

Lesbos Chíos Euboea

Peloponnese

5,095m (16,716ft) H

Kerch

Crimea E 2,267m scarpment (7,438ft)

ea kS Blac nt West arpme Esc

f of

Taganrog anrog Don

439

of Azov

Izmit

des

Athens

Gul

Black Sea

Aegean Sea Spo ra

4,030m (13,222ft)

Thracian Sea Limos

GR EECE

Ionian Basin

ne

Istanbul

ALBANIA

Ioni an Se a

Co

Bosporus Zonguldak

Durrës

A Corfu Pl pul at e

ieper Dn

E ux in e

Burgas

Maritsa

of

Gulf of Taranto

e ub Da n

BULGARIA

Dubrovnik Adriatic Basin Str a Bari it Taranto

Constanta

Danube

L

Mariupol’

Kherson Odesa Sea kinitt r a of K f l u Crimean G Yevpatoriya Peninsula Sevastopol’

Danube

Sava

UKRAINE

Mykolayiv er

K

A

THE ATLANTIC OCEAN

C

100ºW

90ºW

U N I T E D S TAT E S 1

e

M exico B asin

en t

pm

Yuc atan Penins ula

Coatzacoalcos

Carmen

I st mo de Tehuant epec

SOUFRIERE VOLCANO ON MONTSERRAT

4,407m (14,459ft)

Belize City

rough Swan T ahía

e la B as d I sl Puerto Cortés La Ceiba

ATLANTIC OCEAN H2

HUMAN IMPACT

AT L A S O F T H E O C E A N S

Es ca r

Campeche

GUATEMALA

PANAMA CANAL

The Sargasso Sea

Opened in 1914, the Panama Canal links the Atlantic Ocean with the Pacific, allowing ships to avoid the long journey around Cape Horn. Its construction was one of the most difficult engineering projects ever attempted, taking ten years and costing many lives. Each year, 14,000 ships use the canal.

AREA

PANAMA GATES IN 1913

Isla Cozumel

nel

MEXICO

Cancún

Mérida

an

5

k

Ch

Veracruz

mp

Ban

e e ch

he to c e C a ng u To

n

Bay of Campeche

Ca

Es

ent

ata

20ºN

e

pm

Yu ca tan

Tuxpán

Camp

h ec

r ca

eef

Eas tM S h e xi elf co

m

Si gsbee Pl ai n

Fl ori da Pl ai n

rR

4

2,530m (8,301ft)

rp

Gulf of Mexico 3,610m (11,844ft)

Tampico

Esca

yon C an

The Caribbean Sea is a tropical body of water bounded to its south and west by South and Central America, and to its north and east by the Greater and Lesser Antilles. Most of the Antilles, and some parts of the mainland coast, are fringed with coral reefs and small, low-lying islets called cays (or keys). The underlying Caribbean Plate was once part of the Pacific Ocean floor, and it is still moving slowly eastward between the North and South American plates. A subduction zone separates the Caribbean Plate from the Atlantic Plate

r

e

r r ie

25,215 ft (7,685 m)

Atlantic Ocean, Magdalena River

o f Ca nce

be

c Yu

INFLOWS

Tropi c

gs

Ce nt r a l Mis Slope Slope t n

Campeche

MAXIMUM DEPTH

Si

Matamoros

Es Flo ca ri rp

Fan

ippi siss

N o rt h w e s t Brownsville S l o p e

IZE

1.06 million square miles (2.75 million square km)

AREA

Te x a s - Louisia na She lf Padre Island

3

MississippiAlabama Shelf to So on De ny Mississippi Ca

New Orleans

BEL

The Caribbean Sea

Port Arthur

nt

ATLANTIC OCEAN E6

to the east, giving rise to the volcanic island arc of the Lesser Antilles. An east-to-west surface current permeates the whole of the Caribbean, with water from the Guiana Current flowing in via gaps between the small islands in the east, and flowing out in to the Gulf of Mexico via the Yucatán Channel in the northwest. in the northwest.

Corpus Christi

30ºN

da e m

The Gulf of Mexico is almost enclosed by parts of North America. The broad continental shelves to the north and south of the deep central basin are rich in oil deposits.

ande

17,070 ft (5,203 m)

Caribbean Sea; Mississippi, Rio Grande, Apalachicola rivers INFLOWS

Houston

Gr

MAXIMUM DEPTH

r

618,000 square miles (1.6 million square km)

Mobile

2 Ri o

AREA

The Florida Keys are small, low-lying islands composed mainly of ancient coral reefs that are underlain by limestone.

ve

The Gulf of Mexico

FLORIDA KEYS

Ri

ATLANTIC OCEAN B3

Circulation is weak, and the water becomes more salty as it is heated up. Inflows from rivers and the Caribbean are balanced by an outflow of warm, salty water—the beginnings of the Gulf Stream—via the Straits of Florida to the east. This channel runs between two limestone plateaus—the Florida peninsula, above sea level to the north, and the Bahamas, a submerged plateau topped by low-lying islands to the south. The coasts of the Gulf are affected by powerful hurricanes in the late summer and fall.

Red

form a semienclosed extension of the north Atlantic. A low input of fresh water and high evaporation rates make the surface waters highly saline. The area is subject to violent storms and some volcanic activity.

Mississip

THE CARIBBEAN SEA AND GULF OF MEXICO

Ba

The Gulf of Mexico and Caribbean Sea

B

pi

440

6

HONDURAS EL SALVADOR

2 million square miles (5.2 million square km)

MAXIMUM DEPTH INFLOWS

23,000 ft (7,000 m)

NICARAGUA

None

The Sargasso Sea is a large area of the north Atlantic southeast of Bermuda. It is bounded by ocean currents: the Gulf Stream to its west and north, the Canary Current far to the east, and the North Equatorial Current to its south. The area between these currents rotates slowly in a clockwise direction and is often quite calm. Large mats of yellow-brown sargassum seaweed float on its surface, providing shelter and food for communities of small crustaceans and fish, including freshwater eels. Adult eels migrate to the Sargasso every year to mate and spawn, and their young are carried back to the rivers of North America and Europe by the Gulf Stream. Deep water in this part of the Atlantic flows from north to south.

7 10ºN

8

COSTA RICA

PAC I F I C O C E A N

HURRICANE LILI

Hurricanes occur frequently in the Gulf of Mexico and Caribbean Sea, often causing much damage to coastal regions. 90ºW

A

B

C

D

E

F

80ºW

G

H

70ºW

I

60ºW

Nashville Seamount

Norfolk

KEY

OF AMERICA Cape Hatteras

R

a tt

e

dg

e

Blak

Ri

e

a

Bl ak e Bas i n

G r ea t A b a c o Canyon

d

1,600 ft (500 m) 3,300 ft (1,000 m)

5,464m (17,927ft)

R

rm

u

800 ft (250 m)

Soh m Plain

is

H

t en

am

Blake P l at e a u

a

6,500 ft (2,000 m)

30ºN

9,800 ft (3,000 m)

2

16,400 ft (5,000 m)

Sargasso Sea

land seamount

Eastward Knoll Researcher Seamount

sea depth maximum depth on map tectonic plate boundary

3

A T L A N T I C O C E A N

a

Little Bahama Bank

ah

Florida-H

-B

We s t F l o r i d a

id lor t F

a s e r t t H a l a i n P

e

We s

S pu r B l ak e Bla k e Ab y ssa l P la in

Cape Canaveral

Tampa

Be

la k

ah

Jacksonville

Hoyt Hills

B

anat yoBah n am

n

BERMUDA 5,255m (17,242ft)

Esca

as

va n

pe

Richardson Hills

er

Sa

lo

1

te

ra S

Savannah

sea level

s

rpm

Long Bay

Charleston

id

ge

at

Onslow Bay

Myrtle Beach

441

er Ca n c

u

Ex m

t

a

Ex

ce a

tB

eO

ea

f th eo

Gr

a t m en harpm a u

n gu To

Sl

lf he a S

Fort Great c of Lauderdale Bahama Great Trop i Baham a Abaco Island Eleuthera Island Miami BAHAMAS Bas i n re Es B Andros G C c a Nassau o p Fl s Island y e e o r i d a K en d i m Pour tales Es carp F l o r Vema Gap a ma f Cay Sal S Va S Nares Straits o o a l u l ey n d Bank nt a 6,081m Arch a h Plain re a (19,952ft) de S ipiéla aban go Ar n Cm a Long 20ºN Havana TURKS & a de Cc hipi h B a Island é a a l CAICOS n m a a go n n k Golfo gü ISLANDS 5,868m el Acklins Island de Batabano Cienfuegos e (19,253ft) ssag Isla de la a P oir Juventud Great Inagua CU uch n ch BA Mo c o Tr e G r e a t o Ri e e w a r t e 8,962m L r Guantanamo e o i l n a a B a s (29,404ft) P u r Golfo de Yucatan Hisp d rr e Santiago Bay in sage Vir BRITISH s 647m a de Cuba VIRGIN P ge amar I s Guacanayabo Basin p g a M Cap-Haïtien s a i on t u l a 6,691m rd a C (2,123ft)PUERTO n PISLANDS a G Pas in Sp CAYMAN Windwa Cabo Cruz n (21,953ft) a a a e DOMINICAN d g s n d Golfe de la HAITI ISLANDS R i d s d ANGUILLA yo a e a RICO a g San ge g g n s REPUBLIC e a h s Gonâve Juan Tr e n c Montego ANTIGUA & an Barracuda m n Hispaniola a y J 7,680m Jérémie m BARBUDA ST KITTS NAVASSA a y a Ca Santo m C R i dg e Bay Ponce VIRGIN & NEVIS (25,198ft) a i c ISLAND St John’s 5,830m Port-au Domingo a g h ISLANDS eloupe Passage d u (19,128ft) a -Prince o u r MONTSERRAT G sT JAMAICA A n GUADELOUPE Gibbs Muerto Kingston t i l l e s Seamount Basse-Terre inica Passage 5,550m m o (18,210ft) D DOMINICA Pedro 960m Bank ssage (3,150ft) 4,536m inique Pa t r a n M (14,883ft) MARTINIQUE a Venezuelan g u Rosalind Fort-de-France nel Bank ra e ucia Chan a c St L ST LUCIA s i Basin i N R St V ge incent Channel BARBADOS id Bridgetown eR

n

4

C

I s l a n d s

Mo na Pa s

An e An

T

ey

ha

nn

Gulf of Darien

Mag

d

s

s

e

Barbados Trough

l

TRINIDAD

2,319m (7,609ft)

Isla de & TOBAGO Margarita Trinidad Port-of-Spain Gulf of Par ía Cumaná

10ºN

7

VENEZUELA Or inoco

na

Panama City

l

i

e

e

GRENADA

St George’s Tobago

Bonaire 1,390m Isla de Basin (4,561ft) Tortuga Caracas Barcelona

Coro

Lake bo Maracai

Santa Marta Maracaibo Cartagena

L

ale

Volcán Bank Colón Panama Canal

PANAMA

s

a R id

Barranquilla

3,531m (11,585ft)

f lf o a Gu ezuel n Ve

NETHERLANDS ANTILLES

A

r

Tobago Basin

6

SCALE 0

0

COLOMBIA 80ºW

D

200

100

300

100

200

400

8

500 km

300

400

500 miles

70ºW

E

F

60ºW

G

H

I

AT L A S O F T H E O C E A N S

Rióhacha

3,493m (11,460ft)

Limón

Punta Gallinas

s e

Cla r k B asin

Colombian Basin

ST. VINCENT

2,997m (9,833ft)

Lo s Ro q u e s B a s i n ARUBA Curaçao Bonaire Islas los Oranjestad Willemstad Roques

W i n d w a r d

dr Pe

Saury Seamount Mo no Ri

es R idge Gre n B a sn a d a in t

k a Ban

a Gap Arub

4,828m (15,841ft)

4,557m (14,952ft)

Av

Tro dré ug h s gh u

C

rc ala

e rpm ca s oE

Beat

Mos q ui to C M o as t os qu i Sa t o nA Bank n

ge

el

ar Nutib

ro aT

Caribbean Sea nt

Su

5

442

THE ATLANTIC OCEAN

The Central Atlantic

THE MID-ATLANTIC RIDGE, THE WORLD’S LONGEST

mountain chain, is the main sea-floor feature in the central Atlantic. Either side of the ridge are two flat abyssal plains, the Angola and Brazil basins. The dominant Atlantic gyres meet in the central Atlantic. Both are westward-flowing near the Equator, but are separated by the Equatorial Countercurrent, a strong eastward surface flow, and the Equatorial Undercurrent, an even stronger flow 330 ft (100 m) deep. The Canaries Current flows south along the North African coast, becoming the North Equatorial Current. In the south, the cold Benguela Current flows up the African coast, then away from the coast as the South Equatorial Current. This current splits where it reaches PILLOW LAVA Pillows of lava form at the Mid-Atlantic South America, becoming Ridge when extruded lava rapidly cools the Guiana and rather weak upon contact with cold water. Brazil currents. A

B

Paramaribo SURINAM

Cabo Orange

Amaz

ará

Me th

o Amuths azo of n

Macapá

n mazo

Ilha de Marajó

AVERAGE HEIGHT ABOVE SEA FLOOR RATE OF SPREAD

E 20˚W Knipovich Seamount

Four North

ar

á

e Fracture Zon

2,085m (6,841ft)

Zone St Peter and l Fracture St Paul Rocks S a i n t P a u

e dg Ri

Pl

5,024m (16,484ft)

e

on Le rra se e i S Ri

Sa i n t Pe t e r Fr a c t u r e Z o n e

ai

n

1,638m (5,374ft)

São Luís

Fernando do Noronha Plain

Atol das

Sirius 18mRocas Bank (59ft)

Fortaleza

Rom

Fract a n ch e

ure

Fernando do Noronha

Cabo de São Roque

7,728m (25,356ft)

AT L A N T I C 2,677m (8,783ft)

Pernambuco Basin

João Pessoa Recife Maceió

in

6,308m (20,697ft)

Natal

BRAZIL

Zon

Cha

Parnaíba Ridge

2

Pernambuco 2,391m (7,845ft) Plateau Pernambuco Seamounts

5,750m (18,866ft)

Stewart Seamount

Represa de 10˚S Aracaju Sobradinho

3

Stocks Seamount

rra Fe

AT L A S O F T H E O C E A N S

F

30˚W

Maranhao Seamount

A

sea floor gets deeper and older away from the centre, and smoother as its features are covered in sediments. The featureless abyssal plains of the Angola and Brazil basins lie to the east and west respectively. The ridge is displaced east–west at numerous points by transform faults, where the African and South American plates are moving past each other. These fracture zones extend some distance from the ridge, sometimes as active faults where parts of the same plate are moving at different speeds.

D

40˚W

m Belé

Belém

9,800 ft (3,000 m)

1–2 in (2–5 cm) per year

The Mid-Atlantic Ridge dissects the entire length of the Atlantic in a series of rifts and fractures. In the central Atlantic, with relatively narrow continental shelves, it is easy to see where the coasts on either side of the ocean were once joined. The ridge mostly lies 4,900–9,800 ft (1,500– 3,000 m), below sea level, although the volcanoes of Ascension Island and Saint Helena breach the surface. The

677m (2,221ft)

Ce

Ilha de Maracá

Equator

6,200 miles (10,000 km)

LENGTH

Rid

ge

Fan

FRENCH GUIANA

1

Ce

on

Cayenne

4,603m (15,102ft)

Rising just to the west of the Mid-Atlantic Ridge, Ascension Island has 44 distinct volcanic craters.

Mid-Atlantic Ridge

C

50˚W

ASCENSION ISLAND

ATLANTIC OCEAN G3

Salvador

zR

Ilhéus Royal Charlotte Bank

id ge

Gröll Seamount 3,871m (12,701ft) 991m (3,252ft)

Bahia Seamount

Bode

Braz il Basin

Rodgers Seamount

MOUTH OF THE AMAZON

4

The Amazon accounts for nearly 20 percent of the water input from rivers into the world’s oceans, discharging 10.6 million cubic ft (300,000 cubic meters) per second in the rainy season. 20˚S

40˚W

B

C

5,706m (18,721ft)

Hotspur Seamount

11m (36ft)

Vitória

50˚W

A

Abrolhos Bank

Ilha da Trindade D

30˚W

Ilhas Martin Vaz

20˚W

E

F

Ve r d e

e

THE CENTRAL ATLANTIC ATLANTIC OCEAN I1

Gulf of Guinea 500,000 square miles (1.4 million square km) Atlantic Ocean, Niger, Volta rivers

Part of the north Atlantic’s Canaries Current continues along the African coast and into the Gulf of Guinea as the eastward-flowing Guinea Current. The main freshwater input to the gulf is provided by the River Niger, which has an extensive depositional fan, up to 2.5 miles (4km) thick. An even greater source of fresh water for the south Atlantic is from the Congo River to the south. Large oil and gas reserves have accumulated in the sediments of the Niger Delta and Fan, and Nigeria is Africa’s biggest oil producer. Smaller deposits lie in the Congo Fan and in the continental shelf off Gabon, and deeper water in the Gulf of Guinea is now being explored for oil. When the Atlantic Ocean basin started to open 180 million years ago, three rifts opened up in the crust, forming a tectonic G

Although there are doubtless human skeletons on the Skeleton Coast, the ones most likely to be seen are those of rusting ships.

I

IVORY COAST GHANA Abidjan

J

0˚ Volt

Lagos Bight of Benin

Accra Cape Three Points

K 10˚E

NIGERIA

20˚E SCALE

Port Harcourt Douala ght of Biafra e r BiIsla F a n de Bioco Malabo

0

150

300

450

yo an rC a b a l Ca

150

300

KEY

Cap Lopez Port-Gentil

(1,600 ft) (500 m) 3,300 ft (1,000 m)

CONGO

Pierre Brazza Seamounts

DEMOCRATIC REPUBLIC OF CONGO

Pointe-Noire

Zone cture

ANGOLA

5,391m (17,688ft)

3,332m (10,932ft)

800 ft (250 m)

2

6,500 ft (2,000 m) 9,800 ft (3,000 m) 16,400 ft (5,000 m)

n gn C oF a

Rid ge

sea level

Equator

GABON

OCEAN

1

750 miles

600

Congo

600m (1,969ft)

Fr a sion

450

EQUATORIAL GUINEA

Príncipe

Annobón

Ascension Island

750km

CAMEROON

SAO TOME AND PRINCIPE

Guinea Basin

n

600

Cabo San Juan Libreville São Tomé

5,204m (17,074ft)

e e Zon actur

0

n

Three Points Spur

Asce

L

ig

Cape Palmas

Gulf of Guinea

Fr

The cold Benguela Current hugs the west coast of southern Africa and dominates its climate. Although prevailing winds are from the sea, the air above the cold water carries little moisture, and the adjacent coast is a desert. When warm air from the land meets the cold sea air, dense fogs often form. This can be a hazard to navigation, as testified to by the numerous ship hulks along the notorious Skeleton Coast. Even without the fog, any vessel disabled by engine trouble is driven towards the shore by wind and current, and the nearest ports are quite distant. Many sailors who have survived being shipwrecked here have had little choice SHIP’S SKELETON

N

S i e rra Leone B asin

870 miles (1,400 km)

This image, taken from a space shuttle, shows the delta coastline of the Niger River, and sediments being carried offshore.

a

LIBERIA

Secondary coast

LENGTH

NIGER DELTA

H 10˚W

TYPE

Co ng o

INFLOWS

17,070 ft (5,204 m)

Skeleton Coast

er

MAXIMUM DEPTH

but to attempt the arduous journey out of the Namib Desert on foot. Namibia’s coastal waters are dredged for diamonds, as the Benguela Current carries sediments from the Orange River north along the coast. These sediments include large quantities of gem-quality diamonds washed down from the South African interior. A rich fishery is another by-product of the Benguela Current, which causes upwelling of nutrient-rich waters.

ATLANTIC OCEAN K4

Nig

AREA

triple-junction. Two of the rifts continued opening to the south and the west, forming today’s south Atlantic Ocean. Activity in the third rift, to the northeast, ceased rather quickly. The site of this stalled spreading centre is marked by a chain of extinct volcanoes, including the islands of Annabon, São Tomé, Principe, and Bioco in the Gulf of Guinea, and Mount Cameroon inland. São Tomé rises 6,640 ft (2,020 m) above sea level.

443

o

lan ti c t A dMi

land

Ponta das Palmeirinhas Luanda

sea depth

e e Zon Cardno Tablemount

10˚S

A n g o l a Bas i n

384m (1,260ft)

Ponta das Salinas

Bonaparte Seamount

Lobito

3

tectonic plate boundary

ANGOLA

Namibe

ZAMBIA

Ponta Albina

ena

tu Frac

on re Z

e

Saint Helena 5,479m (17,977ft)

H

ast Co

Zubov Seamount

229m (751ft)

0˚

10˚W

4

on

Cape Fria

6,039m (19,814ft)

G

1,600m (5,250ft)

maximum depth on map

let Ske

l t He

Dampier Seamount

NAMIBIA

10˚E

I

J

BOTSWANA 20˚S

20˚E

K

L

AT L A S O F T H E O C E A N S

tur Frac

Sain

seamount

A

444

B

C

70˚W

AR GENTINA

Patagonian S helf 55m

Bahía Grande

1

(180ft)

Falkland Plateau

Stanley East Falkland

2,306m (7,566ft)

FALKLAND ISLANDS

g

Co i

F 50˚W

West Falkland

Punta Entrada

uz

a Cr

E

60˚W

50˚S

Chico

Sant

D

lk Fa

S

Río Gallegos S

50˚

ch

4,528m (14,856ft)

Cape Horn

800 ft (250 m) 1,600 ft (500 m)

P

3,300 ft (1,000 m) 6,500 ft (2,000 m) 9,800 ft (3,000 m)

PA C I F I C OCEAN

16,400 ft (5,000 m)

k ra

D

He

seamount

SCALE

maximum depth on map

0

tectonic plate boundary

S

60˚

0

50

100

50

150

200

e

200

A

B

18,300 ft (5,576 m)

Southern Ocean

The Scotia Sea is bounded by Tierra del Fuego and South Georgia to the north, the South Shetland and South Orkney islands to the south, and the South Sandwich Islands to the east. It is swept by the Antarctic Circumpolar Current, which flows from the Pacific into the Atlantic through the Drake Passage. Part of this flow turns north along the eastern shore of South America as the cold Falklands Current. Where it meets the warm waters of the Brazil Current north of the Falkland Islands,

re Zo ne

C

waters that adjoin it lie between the south Atlantic and the Southern Ocean. Sea ice is present around the region’s shorelines in winter, and icebergs calved from the Antarctic ice sheets can be found year-round.

350,000 square miles (900,000 square km)

upwelling of nutrients supports a rich fishery. The Scotia Plate is moving eastward relative to the South American and Antarctic plates. The separation of South America and Antarctica began around 100 million years ago, opening up a route for Pacific Ocean currents to flow into the young south Atlantic and Indian Ocean basins—the first step in the thermal isolation of Antarctica.

ROCKHOPPER PENGUINS

Ona Basin Fra ct

ure

60˚W

THE COLD SCOTIA SEA AND THE SUBPOLAR

Scotia Sea

co

Zo ne

co h S t ou

ge tia Rid

gh rou T nd nds tla e Isla h d S n tla th he ait S Str th d l u sfie So

70˚W

The Scotia Sea ATLANTIC OCEAN G2

ro Fra ctu

250 miles

80˚W

Protector Basin

a

5,204m (17,074ft)

250 km

150

100

t

Sha W ckle ton

Sars Bank

sea depth

es

S

ti

Elephant Island

land

MAXIMUM DEPTH

e

So u

3

ag s as

S

Isla Hoste

Ya g h a n Basin

End uran ce Fr st F acture ract Zone ure Zone

e

en

Que

Ushuaia Beagle Isla Navarino Channel

g

Tr

44m (144ft)

Isla de los Estados

Tierra del Fuego

i

le

sea level

AT L A S O F T H E O C E A N S

gia

Tehuelche

B ur dwood B ank

Punta de Arenas

Strait of Magellan

id

Punta Arenas Peninsula Brunswick Isla Santa Inés Isla Clarence

KEY

INFLOWS

or h Ge t u o

R

Ch

2

AREA

Tr o u g h

Punta Dungeness

CHILE

4

land

D

ATLANTIC OCEAN B2 AND C2

Strait of Magellan LENGTH

330 miles (530 km)

MINIMUM WIDTH

2½ miles (4 km)

The first European known to have sailed from the Atlantic into the Pacific was Portuguese explorer Ferdinand Magellan, and the strait he used between the South American mainland and Tierra del Fuego is named after him. The route is sheltered from the full might of the Southern Ocean, although it has some narrow passages that can be hazardous to navigate. It was the preferred route for Atlantic–Pacific sea trade until the confirmation of an open ocean route around Cape Horn in 1616. Another sheltered route through the Tierra del Fuego archipelago is the Beagle Channel, named after the survey ship that carried British naturalist Charles Darwin on his scientific voyage of 1831–1836. Cape Horn is the southernmost point of South America, situated on Hoorn Island, one of the Hermite Islands to the south of Tierra del Fuego. The most

Joinville Island an ast Br Co Dundee Island s i v Da ANTARCTICA

Powell Basin

50˚W

E

southerly passage between the major oceans, Cape Horn was discovered and named Kaap Hoorn in 1616 by a merchant navigator, in honor of his sponsors in the Dutch town of Hoorn. However, most commercial traffic between the Atlantic and the Pacific now travels via the Panama Canal.

CAPE HORN

Cape Horn is notorious for its atrocious weather conditions. Sailing around it is the peak of many sailors’ ambitions.

F

G

H

I

J

K 50˚

30˚W

40˚W

L

445

20˚W

S

1,608m (5,276ft)

Northwest Georgia Rise

Ridge

h e ut Ris ia

Ge S or o g

Orc Is ad la as 1,748m (5,735ft)

South Georgia e Fractur

Zone

4,314m (14,154ft)

So u

1,077m (3,534ft)

th

50˚

S

AT L A N T I C OCEAN

8,325m (27,314ft)

2

S

R South Orkney Islands

Orkney Deep B

187m (614ft)

d En

ce an ur

ru

g id

e

c h Is lan ds 3,140m (10,302ft)

th S a n dwi

5,576m (18,295ft)

210m (689ft)

ce

1,780m (5,840ft) 7,152m (23,466ft)

e dg Ri

Lig

eti

Ridg

60˚S

South FractuSandwich re Zo ne

e

SOUTHERN OCEAN 40˚W

G

30˚W

H

ATLANTIC OCEAN J2

South Sandwich Trench LENGTH

600 miles (965 km)

MAXIMUM DEPTH

27,300 ft (8,325 m)

RATE OF CLOSURE

2¾ in (7 cm) per year

J

SEA ICE

Sea ice clings to the shore of Bellinghausen Island, of the South Shetland group, named after the Russian explorer who discovered it in the 19th century.

Mount Belinda, on Montague Island, entered an eruptive phase in 2001, and was still active when this satellite image was taken in 2005.

K

ATLANTIC OCEAN F3

South Georgia Ridge LENGTH

1,600 miles (2,500 km)

HEIGHT ABOVE SEA FLOOR RATE OF RELATIVE MOTION

4

10˚W

20˚W

I

South Sandwich Trench lies a little farther to the east. Both features are caused by tectonic processes occurring where the Scotia and South Atlantic plates meet.The Scotia Plate is split and spreading at the East Scotia Ridge, forming a new plate at its eastern end—the South Sandwich microplate. This plate is geologically young, at about eight million years old, and buoyant. Moving eastward at about 2¾ in (7 cm) per year, it is converging with the South Atlantic Plate, resulting in the older South Atlantic Plate sinking beneath the South Sandwich Plate at a subduction zone.This zone is marked by the South Sandwich Trench and the volcanic island arc of the South Sandwich Islands (or the Scotia Arc).

SOUTH SANDWICH VOLCANO

9,800 ft (3,000 m) ¼ in (0.7 cm) per year

The South Georgia Ridge marks the northern edge of the Scotia Plate, a boundary that continues east through the Tierra del Fuego archipelago. This is a transform boundary (see p.50) with the South Atlantic Plate to the north. There is a similar transform boundary marked by the South Scotia Ridge, with the Antarctic Plate to the south. Fragments of continental crust, such as Burdwood Bank and South Georgia, seem to have been left behind as South America moved west. The island of South Georgia was named by James Cook in 1775, but may have been sighted as early as 1675. It was a base for seal hunters in the 19th century, and

L

in the 20th century seven whaling stations were established on the more sheltered northern shore. The last of these closed in 1965. North of the South Georgia Ridge lies the Falkland Plateau, an area of thickened ocean crust of moderate depth, and the broad continental shelf off the east coast of South America—the Patagonian Shelf. The Falkland Islands are a continental fragment left over from the breakup of Gondwana (see p.44) and the subsequent opening of the south Atlantic. ABANDONED WHALING STATION

Old, rusting whaling ships lie in the harbor at Grytviken, a whaling station from 1904–65, on South Georgia.

AT L A S O F T H E O C E A N S

Although discovered by James Cook in 1775, the South Sandwich Islands were not visited until 1818, when seal hunters landed.They were never permanently settled and remain uninhabited.With volcanic peaks rising up to 3,300 ft (1,000 m) above sea level, the islands are mostly composed of basaltic lava and covered by glaciers. North of the islands is the Protector Shoal— an undersea volcano that rises to within 100 ft (30 m) of the surface.The South Sandwich Islands mark the eastern boundary of the Scotia Sea, and the

3

5,404m (17,731ft)

Sou

Guevara Seamounts

r e n ch

1,139m (3,737ft)

i ch T

Scotia Sea

3,099m (10,168ft)

dw

Ea s t Sc o t i a R i d g e

an

East Scotia Basin

1

s Rise

110m (361ft)

A

B Eu phrates

30˚E Suez

30˚N

rsi Pe

KEY

an G

sea level

1 250m (800ft)

a

3,000m (9,800ft)

1,128m (3.701ft)

Massawa Aden

5,000m (16,400ft)

n Ade

Socotra Raas Caseyr

en

of Gulf

w

Djibouti

O

Berbera

land

Ho r n o f Afr ic a

maximum depth on map

Ch ai n

AFRICA

sea depth

Ri dg e

seamount

Andrew Seamount

Mogadishu

Equator

3

Kismaayo 4,886m (16,031ft)

Mombasa

Basin

Seychelles Bank

Seyc

Dar es Salaam

hell

es

Fred Seamount

Cabo Delgado Comoros Pemba

Mascarene Basin

Comoro Basin

ne l

4

e re n ca u as tea M Pla

Zanzibar

STILT FISHING

Poles are used as perches by some fishermen in Sri Lanka, so as not to scare away the fish.

Somali

Pemba

Tanga

r

asca

dag

Beira

Mahajanga

ie Davge Rid

Moza mb iq

Quelimane

Ma

i

ue Ch an

Zambez

Mascarene Plain Toamasina Mauritius

4,976m (16,326ft)

Réunion

Toliara

Tropic of Capricorn

Durban

eE

M

oz am

Agulhas Plateau

6

biq u

Africana Seamount

7

Atlant ic–I Ridg ndian e

60˚S

Atla 8

Ed wa rd

Agulhas Basin

Fra ctu re

5,819m (19,092ft)

Prince Edward Islands

Del Cano Rise

t es ge w h id ut R S o i a n 4,936m (16,195ft) Ind Crozet Basin

Crozet Plateau

Crozet Islands

Pr inc e

The Indian Ocean floor is dominated by three mid-ocean ridges – the Southwest Indian Ridge, the Mid-Indian Ridge, and the Southeast Indian Ridge – which meet at a triple junction.The Indian Ocean started opening when Africa separated from Antarctica and Australia, achieving its present form when India collided with Asia 36 million years ago. Two long, linear features record India’s rapid movement northwards: Ninetyeast Ridge and the Chagos–Lacadive Plateau. The Indian Ocean has just one large oceanic trench – the Java–Sunda Trench, where the Australian and Indian plates are subducting beneath the Eurasian Plate. The Indian and Australian plates now appear to be moving independently, but the location of their boundary is uncertain.

Ind o

Transkei Basin

(23,042ft)

1,984m Madagascar (6,510ft) Plateau

sca rp

M

Port Elizabeth

men t

oz am

30˚S

Madagascar Basin 7,023m

med Fractur e Zon e

69m (226ft)

Nat al Ba sin

biq ue P lateau

Maputo

5

Ocean Floor

AT L A S O F T H E O C E A N S

Muscat

Se

3,039m (9,970ft)

2,000m (6,500ft)

Ocean Circulation The southern Indian Ocean is dominated by the anticlockwise South Indian Gyre. This drives the South Equatorial Current, which in turn feeds the Agulhas Current. The circulation north of the Equator is complicated by the Indian subcontinent, and the annual wind reversal that characterizes the monsoon climate. High pressure over India from November to April pushes surface water in the Arabian Sea away from India, generating the North Equatorial Current and Equatorial Countercurrent. In the summer, low pressure over India gives rise to southwesterly winds, the Southwest Monsoon Current replaces the North Equatorial Current, and the Somali Current flows strongly northeast along the East African coast.

man

d

SUNRISE IN THE STRAIT OF MALACCA

Jedda

1,000m (3,300ft)

2

Dubai Gulf of O

Re

ocean on Earth, lying between Africa and Australia. Sea routes across the northern Indian Ocean were opened up by traders from the Persian Gulf, and by the Chinese Admiral Zheng He between 1405 and 1433. The Portuguese explorer Vasco de Gama was the first European to circumnavigate Africa, reaching India in 1498.

u lf

60˚E Bander-e Abbas

A r a b i a n Abu Dhabi Peninsula

Tropic of Cancer

500m (1,600ft)

THE INDIAN OCEAN IS THE THIRD-LARGEST

Bander-e Bushehr

re Zon e

The Indian Ocean

C

Fra ctu

THE INDIAN OCEAN

Zo ne

446

Lena Seamount

sin Ba n dia –I n c i t n

5,386m (17,671ft)

Enderby Plain

S OU T H E R N O CE A N

Antartic Circle

INDIAN WATERS

Clear water off the Kenyan coast reveals rock shoals, coral growth, and sand bars.

ANTARCTICA

30˚E

A

B

C

60˚E

E

WINTER SURFACE CURRENTS 90˚E

G an

ASIA

Brahm

ges

us n

Mumbai

Goda

va ri

Ganges F an

20m Goa (66ft) Chennai (Madras)

Arabian Mangalore Basin Laccadive Islands Cochin

Andaman Basin

4,481m (14,702ft)

ne

Trench

Cocos Basin 4.464m (14,646ft)

Ja

va

J n ch a v a R i d g e

Timor North Australian Basin

u Gascoyne ah Plain Wharton 5.678m f Broome el Basin (18.636ft) Sh m t y e x l E Pla ow R Wallaby Port Hedland Plateau Cuvier Basin Cuvier Plateau Carnarvon Batavia Seamount

en R

idge

Ob’ Trench Dia ma

Amsterdam Island St Paul Island

n

Pl

5

Perth Basin Na tu

ntin a

30˚S Perth

Naturaliste Plateau raliste Fracture Z o

Frac ture Zone

Port Augusta Murray Adelaide

Great Australian Bight ne

5,852m (19,200ft)

Melbourne

South Australian B asin

Bass Strait Tasmania Hobart

South Australian Plain

theas

6

Tasman Plateau

t Indian Ridge 7

4,285m (14,059ft)

5,386m (17,671ft)

at

ea

4,684m (15.368ft)

u

184m (604ft) Ba nzare

South Indian Basin

S OU TH ERN OCEA N

Seamounts

60˚S

SCALE 0

Antartic Circle

Pr

yd

zB

ANTARCTICA

ay

E

200

400

600

800

1,000 miles

120˚E

90˚E

D

0

8

200 400 600 800 1,000km

F

G

H

I

AT L A S O F T H E O C E A N S

Heard and McDonald Islands

le

Tropic of Capricorn

ge

t In

Brok

Sou ue

Speed 0–16 kph (0–10 mph) 16–40 kph (10–25 mph) over 40 kph (over 25 mph)

AUSTRALIA

Eas

n Zo

Kerguelen

rg

Beaufort Scale 0–3 3–5.5 over 5.5

lf he lS

4,980m (16,339ft)

Ke

s

Westerlies

S

m

Tra de

o ea uth u

4,023m (13,199ft)

e

da er st Am

re tu ac Fr

ast

ge

5,614m (18,240ft)

INDIAN OCEAN

th E

Java Tr e

7,125m (23,377ft)

e

Osborn Plateau

Ridge

Chagos

MidIn

Basin

Ninetyeast

s–Lacca dive Plateau

Ch ago

So u

tra

Ridge

Equator

ma

Chagos Mid - Indian Archipelago

dia n

Singapore

Su

M

lay la Mainsu P en

Tre n

Ceylon Plain

e a on m Z Veture e c on Fra eZ r ne ctu Zo ra re oF u t g c Ar Fra st e e l Ce rie Ma one eZ Rodrigues tur c a Fr eria Eg

2,078m (6,818ft)

da

on nso Mo t h t u s W e o S

cc a

Investigator Ridg

ar al Se 3,658m (12,002ft)

Maldives

ne Zo

ala

M

re tu ac r kF

4,846m (15,900ft)

ch

re tu ac r F

Zo

3,462m (11,359ft)

SUMMER SURFACE WINDS Phuket

f it o Stra

ss

Colombo

120˚E

n

i ab ah

Nicobar Islands

Sri Lanka

Su

Ca r Ri lsbe d g rg e

Agulhas Current Antarctic Circumpolar Current

Antarctic Circumpolar Current

Andaman Sea

Andaman Islands

Pondicherry

Agulhas Current

Hartog Rid

Arabian Sea

South Equatorial Current

South Equatorial Current

Rangoon Bay of 2,429m Bengal (7,970ft)

shn Kri a

SW Monsoon Current

Equatorial Counter Current

Rid

3,427m (11,244ft)

Somali Current

North Equatorial Current

Tropic of Cancer Chittagong

Kolkata (Calcutta)

a Nar mad

Somali Current

ra aput

dia m an

Karachi ray ur ge M id In R F d a

30˚N

Irrawaddy

us Ind

447

SUMMER SURFACE CURRENTS

Salween

D

448

A

THE INDIAN OCEAN

B

C 40˚E

The Red Sea and Arabian Sea

AREA

175,000 square miles (450,000 square km)

MAXIMUM DEPTH INFLOWS

9,975 ft (3,040 m)

Arabian Sea

AEL

2 1,929m (6,329ft)

360 ft (110 m)

Tigris, Euphrates, Karun rivers

Tropic

Râs Banâs of Ca

ncer

MOVING OIL

Much of the ship traffic in the Persian Gulf and Red Sea today carries oil from the region’s production fields.

3

Jedda 20˚N

(9,970ft)

SUDAN

ea d S

Ras Shakal

4

SAUDI ARABIA

Re

Port Sudan 3,039m

ugh Tro

The Persian Gulf (also known as the Gulf) is a warm, semi-enclosed sea, mostly less than 330 ft (100 m) deep. It is connected to the Arabian Sea via the Strait of Hormuz and the Gulf of Oman. The shallow waters are well mixed and more productive than the Red Sea owing to the nutrient runoff from the land to the north and east. Corals have adapted to the very warm water temperature, which can reach 91°F (33°C). The Arabian Plate, spreading from the Red Sea rift, is moving northeast and sliding under the Eurasian Plate, so the northeastern side of the Persian Gulf is deeper. This tectonic activity has folded and uplifted sediments up to 280 million years old and produced structural traps for oil, which has accumulated in large reservoirs beneath the Gulf and surrounding land. Oil now dominates the region’s economy.

KUWAIT

Suakin

THE SUEZ CANAL

INFLOWS

Eu phrates

Al ‘Aqabah Gulf of Aqaba

Bûr Safâga

93,000 square miles (241,000 square km)

MAXIMUM DEPTH

IRAQ

JORDAN

ry cove Dis sin Ba

The Red Sea is an embryonic ocean, and it has been opening over the last 25 million years, ever since the Arabian Plate began its gradual rift away from Africa. A central trough is flanked by relatively shallow shelves, and its warm waters contain many fringing coral reefs. Since 1869 the Red Sea has been linked with the Mediterranean Sea via the 100-mile(160-km-) long Suez Canal.

AREA

ERITREA Massawa

Dahlak Archipelago

Jaza’ir Farasan

5 INDIAN OCEAN G5

Arabian Sea AREA

1.5 million square miles (3.9 million square km)

MAXIMUM DEPTH INFLOWS

19,038 ft (4,481 m)

Indus, Namada rivers

The Arabian Sea lies between the Arabian Peninsula and India. It is underlain by the abyssal plain of the Arabian Basin. This oceanic part of the Indian Plate is bounded to the west by the Owen Fracture Zone

and to the south by the Carlsberg Ridge, where India and Africa are diverging. To the west lies the Gulf of Aden, a precursor to the Red Sea rift, with a well-established spreading ridge. On the northern shore, earthquakes within the Makran subduction zone sometimes trigger the eruption of mud volcanoes. One of these appeared suddenly as a new island off the Pakistani town of Gwadar in 2013. Such features usually subside within a few months.

s

Elat

Sharm el Sheikh

INDIAN OCEAN D2

Persian Gulf

EGYPT ez f Su

Indian Ocean uniquely reverses twice a year due to the monsoon winds. For thousands of years, navigators used this to run trade routes in the region. Today, oil and the Suez Canal make the area strategically important.

Red Sea

Suez Gulf o

CIRCULATION IN THE NORTHEAST

INDIAN OCEAN B4

ISR

1

Ti

gri

Suez Canal 30˚N

YEMEN

Hodeida

Al Mukalla Bab el Mandeb Aden DJIBOUTI

6

Tadjoura Trench

he b West S

Djibouti

KEY sea level

854m (2,802ft)

a Ri

dge

en Gulf of Ad Boosaaso

10˚N

800 ft (250 m)

Berbera

1,600 ft (500 m)

AT L A S O F T H E O C E A N S

INDIAN OCEAN I8

Maldives TYPE AREA:

Coral atoll islands 115 square miles (298 square km)

NUMBER OF ISLANDS

1,192

The Maldives lie midway along the Chagos–Laccadive Plateau. The Laccadive Islands and a number of submerged banks mark the northern end of the ridge. There are more than 1,000 Maldive islands, grouped into 27 atolls, composed of coral and sandbars. The highest island is less than 10 ft (3 m) above sea level. With

a warm climate, shallow lagoons, and refreshing sea breezes, the Maldives are an idyllic vacation destination. Although tourism plays an increasingly important role in the economy of the islands, fishing remains the main occupation of the islanders.

3,300 ft (1,000 m) 6,500 ft (2,000 m) 9,800 ft (3,000 m)

7

16,400 ft (5,000 m)

SOMALIA

ETHIOPIA

MALDIVE ISLAND land seamount sea depth

8

maximum depth on map tectonic plate boundary

50˚E

40˚E

A

B

C

D

E

F

50˚E

G

H

60˚E

I

449

70˚E

80˚E

SCALE 0

200

100

300

400

500 km

1

AF G HAN I STAN 0

100

300

200

500 miles

400

30˚N

IRAN Bandar-e Bushehr

Bandar-e `Abbas Qeshm

Manama

ANCIENT TRADE ROUTES

Dhows, the traditional Arab sailing vessels, were used to establish trade routes across the northern Indian Ocean up to 5,000 years ago. Trading posts were set up along the shores of East Africa and India.

Strait of Hormuz OMAN

QATAR

Al Fujayrah

Doha

Dubai Abu Dhabi

Gul f of O

man

3,345m (10,975ft)

d

u

Khambat

Gulf of Kachchh

s

Fa

n

Porbandar

M

ur

ra

y

Ra’s al Hadd

id

ge

Bhavnagar Kathiawar Peninsula

Veraval K f of Gul

3,427m (11,244ft)

g an ria k

Z o n e

Raman Guyot

F r a c t u r e

Al ul a Tre -Far nc tak h

20m (66ft)

5

A rabian

Cora Diva Bank

Sea

e n

Cherbaniani Reef

w

Ara bi a n Ba s i n

O

Byramgore Reef

Ryurik Seamount

e

s

b

ha

in

Ri

dg

l

3,169m (10,397ft)

e

Colvocoresses Reef

r

3,017m (9,899ft)

g R

C

Somali Basin

1,333m (4,380ft)

E

F

Male’

MALDIVES

i

d

g

e

INDIAN OCEAN

60˚E

D

7

u t e a P l a

Andrew Tablemount

r

6

70˚E

G

H

I

8

AT L A S O F T H E O C E A N S

C

10˚N

Minicoy Island

Sagar Kanya Seamount

Serendip Seamount

a

Laccadive Islands

1,880m (6,168ft)

4,481m (14,702ft)

Bunce Seamounts

Mangalore Bassas de Pedro Bank

Sesostris Bank

Error Tablemount

Camões Seamount

Goa

Panikkar Seamount

Zheng He Seamount

Raas Xaafuun

4

INDIA

e d i v c a a c – L o s a g C h

Raas Caseyr

20˚N

Mumbai

2,769m (9,085ft)

e

Socotra

b ham

AnB

g

Surat

t y ft F l a Fi s m

Ra’s Madrakah Dawhat Sawqirah Ras Sharbithat Khalij al Halaniyat

Ea s t S h e b a R i d

3

a

mad

ho

Khalij Masirah

Ghubbat al Qamar Ra’s 1,128m Fartak (3,701ft)

Nar

ha

Fa T h t e

Jazirat Masirah

OMAN

er

f Canc

o Tropic

M theouths Ind of us

Oman Basin

Muscat

Sonmiani Bay Karachi

Gwadar

In

UAE

Makran Co ast

t

lf

s

Gu

Indu

an

Ad Damman BAHRAIN

2

PAK I STAN

R

Pe

rsi

B

C

D Ga

80˚E

90˚E

nges

450

600

750 km

sea level

LAOS

Baleshwar Mouths of the

1 0

150

450

300

Sittwe

35m (115ft)

Ramree Island Cheduba Island

ava ri

INDIA

2,807m (9,210ft)

Kakinada

na

Ga

Pondicherry

nges

Fan

Bay of Bengal

Nagappattinam

ait Str lk Jaffna a P

Ten Deg ree Channel

THE NORTHEAST CORNER

of the Indian Ocean is enclosed on three sides by land. This area of tropical sea is subject to a monsoon climate, and vulnerable to cyclones between the months of June and November.

Bay of Bengal AREA

1.1 million square miles (2.9 million square km)

MAXIMUM DEPTH

15,400 ft (4,695 m)

Ganges, Brahmapurta, Mahanadi, Godavari, Krishna, Kaveri, Irrawaddy rivers INFLOWS

Circulation in the Bay of Bengal is clockwise during the northwest monsoon, with a westward flow in the main ocean. This flow reverses during the southwest monsoon. The northern half of the bay is underlain by the Ganges Fan, a thick cone of sediment extending from the continental rise across the abyssal plain. This is the fastest-accumulating sediment in the world, originating high in the Himalayas, and supplied by the Brahmaputra River and the Ganges.

INDIAN OCEAN F4

Strait of Malacca LENGTH

600 miles (963 km)

MINIMUM WIDTH

9 miles (15 km)

The Strait of Malacca links the Indian Ocean with the Pacific Ocean, via the South China Sea. About 140 ships pass through this busy waterway daily. The cargo includes about one quarter of the world’s oil, headed from the Persian Gulf to markets including Japan and China. Such heavy traffic led to a big rise in piracy in the 1990s, although attacks have dropped with the advent of tougher naval patrols since 2005. The world saw 297 pirate attacks in 2012 (down from a peak of 439 in 2011), with the worst of the problem now being off east and west Africa.

St Belawan

Su

Pulau Simeulue

h

Cocos Basin D

INDIAN OCEAN E3

Andaman Sea AREA

308,000 square miles (798,000 square km)

MAXIMUM DEPTH

12,400 ft (3,777 m)

Bay of Bengal, Strait of Malacca; Irriwaddy, Salween rivers INFLOWS

The Andaman Sea lies between the Andaman Islands, Sumatra, and the Malay Peninsula. There is a broad continental shelf in the east and the north, where the sediment is dredged for cassiterite, an ore of tin. Alcock Rise and Sewell Rise are separated by an area of deep ocean floor, where a spreading center has been pushing the Burma and Sunda microplates apart for the last 3–4 million HAVELOCK ISLAND

Mangroves line the eastern shore of Havelock Island, part of the Andaman Islands group. These volcanic islands are also fringed by coral reefs.

Pulau Nias

E

m

at

ra

it

ns

C

The Bay of Bengal INDIAN OCEAN C2

Banda Aceh

90˚E

B

Pulau George Langkawi Town Pulau MALAYSIA Pinang

ni

A

241m (791ft)

nc

3

Krabi

Pe

80˚E

Dreadnought Bank

e

Equator

Nicobar Islands

Tr

Ceylon Plain

4,846m (15,900ft)

10˚N

Ko Phuket Phuket

a

4,217m (13,836ft)

Mergui Terrace

nd

4

Sewell Rise

Roe Bank

tectonic plate boundary

Su

INDIAN OCEAN

Andaman Basin

maximum depth on map

ay

Dondra Head

Andaman Sea

sea depth

Mergui

al

Galle

seamount

M

3,462m (11,359ft)

N i ne tye as t

Colombo

Ridg e

Toticorin

2

land

Alcock Rise

Port Blair

16,400 ft (5,000 m)

Gulf of Martaban

Andaman Islands

3,462m (11,359ft)

SRI Batticaloa LANKA

Moulmein M the outh Irra s of wadd y 18m (59ft)

Invisible Bank

10˚N

Cape Comorin

3,300 ft (1,000 m) 6,500 ft (2,000 m) 9,800 ft (3,000 m)

THAILAND

go Mergui Archipela

Chennai (Madras)

Coroman

2

del Co ast

Machilipatnam

Gulf of Mannar

1,600 ft (500 m)

Rangoon

Bassein

2,429m (7,970ft)

1

800 ft (250 m)

Visakhapatnam

Kr is h

3

waddy Irra

Puri

20˚N

MYANMAR

Ganges

750 miles

600

Go d

AT L A S O F T H E O C E A N S

KEY

Isthmus of Kra

300

150

F 100˚E

Tropic of Cancer

Kolkata (Calcutta) BANGLADESH Chittagong

SCALE 0

E

Salwee n

A

450

of

u

Ma

ra

Klang l a l a c Melaka Johor ca Bahru Singapore

INDONESIA

SINGAPORE

Equator

100˚E

F

years. This divergence created the Andaman Sea. The eastern half of the sea lies over the Sunda Plate, which includes most of Sumatra and the Malay Peninsula. The western half includes the Andaman and Nicobar Islands and sits on the Burma Plate, which forms a junction with the Indian Plate at the Sunda Trench. At this subduction zone, the Indian Plate is being overridden by the younger Burma Plate. The southern part of this zone was the source of the 2004 Indian Ocean tsunami.

4

THE JAVA TRENCH

The Java Trench , the South Equatorial

Timor Sea

Current carries water from east to west during the southwest monsoon, but shifts south during the northeast monsoon to be replaced by the eastward-flowing Equatorial Counter Current. The area includes the deepest part of the Indian Ocean, the Java Trench, where the Australian Plate meets the Eurasian Plate.

MAXIMUM DEPTH

23,377 ft (7,125 m)

RATE OF CLOSURE

21/2 in (6 cm) per year

The Java Trench is a continuation of the Sunda Trench, where the oceanic part of the Australian Plate is being subducted beneath the continental Eurasian Plate. A string of volcanoes has resulted behind the trench, strung out across Sumatra, Java, and the Lesser Sunda Islands. The Australian Plate is moving north at a rate of 21/2 in (6 cm) per year. The Indian Ocean floor A

n

R i d g e

Makassar

Flores Sea

Roo Rise

Basin

th ou au e Barrow Island North West Cape

Ex Pl m at

750 km

450

600

90˚E

750 miles

100˚E

B

3,540m (8,334ft)

Cuvier Plateau

Ro

Sh ar k

D

Sh

e

Dili EAST

TIMOR

Savu Timor Sea

rou or T m i T

hu Sa

y wle

s nk Ba

Broome lf

2

gh 10˚S

Timor Sea

Cape Londonderry

lf he S l 3

Derby

20˚S

Port Hedland

Tropic of Capricorn

Carnarvon

AU ST R A L I A

110˚E

C

Savu Basin

Coral Bay

Cuvier Basin

Dirk Hartog Island

Batavia Seamount

Pulau Sumba

5,718m (18,761ft)

y Ba

300

600

Pulau Wetar

Rowley Shoals

Wallaby Lo Plateau st Du tch m en Ri d

Ea

450

Flores

North Australian Basin

Gascoyne Plain

Banda Sea

Bone Basin

Flores Basin

Sumbawa

Lombo k

1

Pulau Buru

Lesser Sunda Islands

Bali

as

120˚E

E

F

4

AT L A S O F T H E O C E A N S

N i n t e y e a s t

n g Seamount 2,619m Me (8,593ft) ine sz Se am oun ts

164m (538ft)

Teluk Tolo

Celebes

South Makassar Basin

Bali Sea

Surabaya

Ja Trou v a v a R gh idg a Christmas e Island 7,125m T (23,377ft) r e Shcherbakov n ch

J

st Ind iam an R idge

Mid-In dian Basi

Java

Kepulauan Sula

cc

Su nda

lu Mo

4,023m (13,199ft)

150

A

Banjarmasin

Java Sea

ge

0

ni

f

Bandarlampung Jakarta Semarang

5,678m (18,636ft)

300

150

Ve

Balikpapan

Molucca Sea

Gulf of

Tomini North MakassarPalu Basin

Wharton Basin

SCALE 0

Manado

ne

4

Pulau Belitung

aw ai Ba ai sin R i T id ro ge ug h

4,846m (15,900ft)

Borneo

Samarinda

I N D O N E S I A

INDIAN OCEAN

5,887m (19,315ft)

120˚E

Teluk Bo

Osborn Plateau

20˚S

Bengkulu

e w M ta a en w M enta M

Cocos Islands

Investigator Ridge

4,464m (14,646ft)

1,517m (4,977ft)

3

Pulau Bangka

nt

10˚S

F

Equator

Pontianak

el Sh da Sun

ai taw en ai M aw lat ent M

2

Natuna Kepulauan Sea Lingga

Sumatra

5,759m (18,895ft)

Cocos Basin

E

110˚E MALAYSIA

Singapore

Padang

an lau

4,610m (15,125ft)

D

SINGAPORE

Se

Ceylon Plain

Traditional, shore-based fishing is practiced by Timorese fishermen, seen here hauling in a net at Areia Branca Beach near Dili.

MALAYSIA

100˚E

Pulau Nias pu Ke

1

TIMOR FISHERMEN

C

90˚E

10,800 ft (3,300 m)

Indian Ocean, Arafura Sea

The Timor Sea marks the eastward boundary of the central Indian Ocean. Pacific water flows in from the Arafura Sea (see p.473) during the southwest monsoon, feeding the South Equatorial Current. This flow is reversed during the northeast monsoon. Australia’s aboriginal people probably arrived from southeast Asia by island-hopping across the Timor Sea. It is mainly shallow, but with the deep Timor Trough lying along its northern edge. Significant reserves of oil and gas are

south and west of the trench shows tectonic features aligned in this northerly direction. Between Investigator Ridge and Ninetyeast Ridge lie a series of north–south fractures formed to accommodate different rates of motion in the Australian and Indian plates. The Ninetyeast Ridge itself is the longest underwater mountain chain, at 3,100 miles (5,000 km) in length. It followed in the wake of India’s rapid motion north as the Indian Ocean opened up. The ridge represents piles of extruded volcanic material formed above the Kerguelen Hotspot, and were carried north as the sea floor spread between India and Antarctica.

B

Equator

INFLOWS

l

1,600 miles (2,600 km)

LENGTH

235,000 square miles (610,000 square km)

MAXIMUM DEPTH

Sa hu

Java Trench

AREA

Ma kas sar Str ait

INDIAN OCEAN D2

thought to lie in the continental shelf sediments beneath the sea, and exploitation rights are disputed between Australia and East Timor. The warm shallow tropical waters make the Timor Sea a breeding ground for tropical storms and cyclones from January to March. Such storms proceed southwestward into the Indian Ocean, sometimes turning inland to hit the coast of Western Australia. There are fishing grounds, including a shrimp fishery, in coastal waters on the Australian side of the Timor Sea.

INDIAN OCEAN F2

IN THE EASTERN INDIAN OCEAN

451

THE GANGES DELTA

Where the Ganges and several other rivers empty into the Bay of Bengal, on the coast of Bangladesh and northeastern India, the world’s largest delta has formed. In this satellite image of a part of the delta, the dark green areas are a mangrove forest known as the Sundarbans. The lighter green areas are cultivated land.

A

454

B

C

D

40˚E

F

50˚E

Coco-de-Mer Seamounts

Kismaayo

sea level

1 Tana

KENYA

1,600 ft (500 m)

Pate Island Ke N ny ort a h Ba nk

3,300 ft (1,000 m) 6,500 ft (2,000 m) 9,800 ft (3,000 m)

Mombasa

di Ri ngle se y

Seyc h

Pemba

land

Zanzibar

ea

u

ji

at

Rufi

Pl

Group

Giraud Seamount

ne

Aldabra Group

TANZANIA

3

Anton Bruun Ridge Providence Reef Farquhar Bulldog Group Bank

914m (3,087ft) Cosmoledo

c en Tr

Wilkes Rise

re

Mafia

ca

SEYCHELLES

Rufiji

ne rtu Fo ank B

tectonic plate boundary

Fred Seamount

n te Amira

maximum depth on map

Dar es Salaam

as

Zanzibar

sea depth

Basin

M

seamount

elle sB Inner Amirante Islands

Victoria

k

Amirante Islands

an

Tanga

2

10˚S

Ma

e

16,400 ft (5,000 m)

4,886m (16,031ft)

Somali Basin

Amirante R idg

800 ft (250 m)

60˚E

191m (623ft)

SOMALIA

Equator

KEY

E

h

Ritchie Bank

Agalega Islands

Cabo Delgado Grande Comore

COMOROS

Moroni

Anjouan

Mohéli

Lake Nyasa

Geyser Reef

Leven Bank

MAYOTTE

Pemba

4,801m (15,752ft)

Tanjona Bobaomby Bardin Seamount

Nosy Be

Comoro Basin

Wormley Seamount

INDIAN

3,301m (10,831ft)

Mo

Sofala Ilha do Bazaruto

e g

id W

Jaguar Seamount

ihin a

La Pérouse Seamount

Tanjona Ankabna

4,976m (16,326ft)

y Mangok

RÉUNION

Île Europa

Soudan Bank

sh

Port Louis

MAURITIUS

Mascarene Islands

Toliara Inhambane

69m (226ft)

8

ique P lateau

7

Tropic of Capricorn

Mo z amb

AT L A S O F T H E O C E A N S

il

St-Denis

Bassas da India Hall Tablemount

Mascarene Plain

Toamasina

M au rit

20˚S Baia de

Tsirib

yon Can

6

Nosy Sainte Marie

MADAGASCAR

zi be

Beira

Za

m

zam

PontaTimbue

Cargados Carajos Bank

Tanjona Masoala

iu sT re nc h

ue

e zi

biq

Za mb

Tromelin

Mahajanga

Tanjona Vilanandra

Betsiboka

Ch

an

5

Davie Ridge

ne

l

MALAWI

R

MOZAMBIQUE

Quelimane

Mascarene Basin

Antsiranana

w

4

Hydra Seamount

Nosy Glorieuses

Natal Basin

Tanjona Vohimena

M adagascar Plat eau

Madagascar Basin 7,023m (23,042ft) 1,984m (6,510ft)

4,769m (15,647ft) 50˚E

40˚E

A

B

C

D

Nazareth Bank

uma

a

Ruv

60˚E

E

F

G

H

I 70˚E

Zo ne

ve Plateau

MA LD IVES

tu re

Zo ne

Fr ac

Fr a

–L

e n

10˚S

c ra

tu

re

ne

ste ele C rie Ma

ct Fra

s Ridge

Rodrigues

Mozambique Channel

ri ge

F

a

Mid-Indian Basin

e

INFLOWS

5

c ra

tu

re

Zo

ne

20˚S

Zambezi, Rio Lúrio rivers

The Mozambique Channel separates Madagascar from the mainland of Africa. The area is home to the ancient coelacanth, found on both sides of the channel and off the Comoros. A counterclockwise gyre is found around the Comoros, and counterclockwise eddies dominate the flow in the main part of the channel. The warm Aghulas Current arises over the Natal Basin, fed by the South Equatorial Current.

INDIAN OCEAN F6

-In

Mauritius and Réunion

dia 7

e 400

8

500 km

TYPE

Volcanic islands

AREA

1,800 square miles (4,550 square km)

NUMBER OF ISLANDS

2

The Mascarene Islands, Mauritius and Réunion, are the largest and youngest islands associated with the Mascarene Plateau, rising 21,300 ft (6,500 m) above the sea floor. Like the older banks of the plateau to the northeast and the Rodrigues Ridge to the east, they are volcanic in origin, having formed FRINGING REEF

0

100

200

300

500 miles

400

70˚E

G

H

I

south. This continental fragment broke off from India around 65 million years ago as the current Mid-Indian Ridge started spreading.

INDIAN OCEAN H3

Mid-Indian Ridge LENGTH

2,100 miles (3,400 km)

AVERAGE HEIGHT ABOVE SEA FLOOR RATE OF SPREAD

5,000 ft (1,500 m)

11/4 in (3 cm) per year

The Indian and African plates are moving apart due to spreading at the Mid-Indian Ridge, which is marked by a series of transform fracture zones. Rifting was triggered 65 million years ago when the Réunion Hotspot erupted a vast amount of basalt through the Indian continental plate, forming a plateau called the Deccan Traps. An older spreading ridge, which first separated India from Africa, lies subsided between the Mascarene Basin and the Mascarene Plain.

A reef fringes the lagoon on the north coast of the volcanic island of Mauritius.

above a deep mantle hotspot. After the Deccan Traps eruption (see above), the Réunion Hotspot continued to punch through the crust as India moved north, leaving a trail of volcanic structures across the ocean floor, including the Laccadive and Maldive islands and the Chagos Bank on the other side of the Mid-Indian Ridge. Réunion’s main peak, Piton de la Fournaise, is one of the most active volcanoes in the world.

AT L A S O F T H E O C E A N S

idg n R

Tropic of Capricorn

e an R idg

300

370 ft (110 m)

GRANITE BOULDERS IN THE SEYCHELLES

6

2,078m (6,818ft)

200

386,000 square miles (1 million square km)

MAXIMUM DEPTH

Mid

E

ndi st I e w th SCALE u 0 100 So

INDIAN OCEAN B5

AREA

on eZ r u

115

The main islands of the Seychelles— the Inner Islands—are made of granite, rising over 3,000 ft (900 m) above sea level on top of the Seychelles Bank. The other islands to the southwest—the Outer Islands— are coral islands (atolls) on top of seamounts. The Seychelles Bank is the most northerly part of the submarine Mascarene Plateau, which extends as far as the island of Réunion in the

4

o

569m (1,869ft)

Continental islands

176 square miles (455 square km)

NUMBER OF ISLANDS

Zo

OCEAN

rigue

AREA

Diego Garcia

Zo

Seychelles VOLCANIC

Ch

Ch

ag

agos Arc h ipelago Cha gos Tre nch

os

n Ri dge a

F

g Ar

Ro d

INDIAN OCEAN D3

2

Chagos Bank

dia m

Fr

re

The Seychelles and Madagascar

ac

rk Se al a

Ve

a

u ct

455

THE EASTERN INDIAN OCEAN FLOOR is littered with scars documenting the breakup of Gondwana over the last 150 million years. The warm waters of the Indian Ocean have also proved to be an ideal environment for diverse marine life.

4,301m (14,112ft)

-In

Saya de Malha Bank

1

3

id M 6,102m (20,021ft)

Equator

cadi

ct ur e

M ab ah is s 3,658m (12,002ft)

Alix Seamount

THE SEYCHELLES AND MADAGASCAR

A

THE PACIFIC OCEAN

B

C

120ºE

The Pacific Ocean

150ºE

KEY sea level

Arctic Circle

1 800 ft (250 m) 1,600 ft (500 m)

s

lau R

Kyushu-Pa

aT ren ch

idge

y re uk y nc u h

St r

Ta iw an

Str

New G ou gh

t

Banda Sea

uin ea

Solomon Sea Coral Sea Basin

B

ie r

R ee

f Tas ma nP

Tasman e on eZ

Balleny Islands

A N TA R C T I C A SCALE 1,000

1,500

2,000

2,500 km

EAST PACIFIC RISE

Pillow lavas are extruded at all mid-ocean ridges and form the top layer of the crust throughout the oceans.

0

500

1,000

1,500

2,000

120ºE

A

2,500 miles

150ºE

B

e

Ma cq ua r ie

tur Frac

Ri dg

5,369m (17,616ft)

Antarctic Circle

500

Ris

Tasman Sea

S O UTH E R N O C E A N

0

e

trait Bass S Tasmania

8

New Caledonia

Ris

6

7

1,577m (5,174ft)

Brisbane

Sydney

Ocean Basin

n

Isla nds

Lord Howe

AU S T R A L I A

mo n

Coral Sea a rr

30ºS

60ºS

iy

M e l Solo a

at

Tropic of Capricorn

lan es ian

Ontong Java Rise

Townsville

The north Pacific is a breeding ground for storms. Here the bow of a ship plows through violent storm waves in the Bering Sea.

AT L A S O F T H E O C E A N S

I s l a n d sMe

Bismarck Sea

Gre

I N DI A N O C EA N

ROUGH SEAS

The Pacific Basin has been shrinking since the opening of the Atlantic and Indian oceans. It has more subduction zones, where oceanic crust is consumed, than any other ocean.Violent volcanic eruptions are associated with these zones, producing the Ring of Fire around the Pacific’s shores (see p.184). The western Pacific is studded with chains of volcanic islands and marked by deep ocean trenches where the Pacific Plate meets the continental Eurasian Plate and smaller oceanic plates. The floor of the eastern Pacific is fairly smooth in comparison, sloping gently away from the coast of North America and the East Pacific Rise. Mid-ocean island chains and seamounts have arisen from intermittent eruptions above mantle hot spots.

d-P M acifi c

6,464m Ma ge (21,208ft) ll a nS East ea m Mariana ou Basin nt s

East Caroline Basin

Port r Arafura Moresby T r Sea o im Arafura Shelf TimorT

Ja va

ker ma ap

M i c r o n e

West Caroline Basin

ait

ma

Maka ssar

ch en Tr

Sea

West Mariana Basin

Moluccas

Celebes

Mi

an Mari 10,057m Challenger Deep (32,997ft) 10,920m Palau (35,829ft) Caroline

h Trenc

Su

Borneo

Java Sea

Jakarta

ine

Davao

Makarov Seamount

in Bon

ng

Shelf Equator Singapore

Philippine Basin

Celebes Sea

9,780m (32,088ft)

Basin

lipp Phi

e ko

South China S unda Sea

ra

5

Philippine

Manila South China Basin Philippines

6,650m h (21,817ft) S

Shikoku

R 7,460m T (24,476ft)

Hainan Dao

M

4

China Sea t aiTaiwan

Hong Kong

Tropic of Cancer

at

Shanghai Sea Kyushu 30ºN East

maximum depth on map

Ho Chi Minh

Pa cific Ba sin

Yellow

sea depth

Gulf of Thailand

Honshu East Sea Toyko

Pusan

sk

Qingdao

seamount

e

nd

land

Jap Trenan ch

16,400 ft (5,000 m)

Ocean Circulation The Pacific is cut off from the Arctic Ocean, but exchanges water with the Southern Ocean. The North Equatorial Current is the world’s longest westward-flowing current, carrying water 9,000 miles (14,500 km) across the ocean. The warm Kuroshio Current flows north as the North Pacific’s western boundary current, and the Kuroshio Extension returns warm water to the western Pacific. The counterclockwise gyre in the South Pacific is formed by the South Equatorial Current, the warm East Australia Current, the Antarctic Circumpolar Current, and the Humboldt Current. A strong upwelling occurs where the cold Humboldt Current diverges from the coast, but this routinely fails as part of the El Niño Southern Oscillation (see pp.68–69).

Petropavlovsk890m Kamchatskiy r (2,920ft) A mu sin h Ba s l a n c Kurile i l e I Tr e r u K r i l e 9,783m Vladivostok Japan Hokkaido K u (32,098ft) Sea of Basin Nort hw e st Namp’o Japan/

ASIA

9,800 ft (3,000 m)

3

Ostrov Sakhalin

ok u

BORA BORA ISLAND IN THE SOUTH PACIFIC

Sea of Okhotsk

6,500 ft (2,000 m)

2

ka at la c h nsu i

Magadan

3,300 ft (1,000 m)

k Shi

It is twice the size of the Atlantic and covers more than a third of the planet’s surface. Many Pacific islands were colonized by Micronesians and Polynesians before Europeans arrived in the 16th century. The Portuguese explorer Ferdinand Magellan died after crossing the Pacific in 1521, leaving his crew to complete the first circumnavigation of the world.

K Pe am n

THE PACIFIC IS THE LARGEST OCEAN.

295m (968ft)

60ºN

lai n

456

C

E

F 150ºW

457 Oyashio

120ºW

Yukon River Anchorage

N O RT H AMERICA

Queen Gilbert Se amo Charlotte un 5,267m Islands ts (17,281ft) Vancouver

San Francisco o d Colora Los Angeles

Mathematician Seamounts s

e Ris

st P acifi

e

ge

Sout hw es t Pac i fic Bas i n

Chatham Islands

Me

Bollons Tablemount

Campbell Islands

P a c i fi c – A n t a r c t i c

ints

ev Fr act

nin F ractu

ure Z one

Fra ctu

re Zon e

fo Fr G ua

es

id ge

5 8,069m (26,474ft) Tropic of Capricorn

Valparaíso

6

e Zone actur

Punta Arenas

Cape Horn ge assa ke P Dra 60ºS Bellingshausen Plain la n i su enn P ctic Antarctic Circle

6,034m (19,798ft)

S O UT HER N O C EA N

30ºS

Ris e

Mo rn i n g t o n A b y s s a l Plain

Southeast Pacific Basin

sen Plain Amund

e Zone

Chile

re Zone

g e R i d 4,283m (14,058ft)

nger F ractur

1,426m (4,679ft)

en

Bellingshausen Sea

7

Amundsen Sea

Ross Sea 8

Ross Ice Shelf

A N TA R C T I C A

180º

D

150ºW

E

120ºW

F

90ºW

G

60ºW

H

I

AT L A S O F T H E O C E A N S

Ud

5,415m (17,767ft)

Elta

nard

Challe

Tr

Per

c Rise

ill

id

e

Chile Ba sin

Ro g g e v e e n Basin

Ea

nc h

To Tre nga nch sv

Ker m Tre adec nch

Easter a l a y G o m e z R i d g e S r F r a c Island ture Zone

cture Zone siz Fra Agas R

Pe ru

a e Basin G re Zon Mendaña Fractu

Yupanqui B asin

SOUTH AMERICA

Lima

ch

Easte

Galapagos Islands

B auer B asin 5,852m (19,200ft)

Speed 0–10 mph (0–16 km/h) 10–25 mph (16–40 km/h) over 25 mph (over 40 km/h)

l

a

rn C ook Islands

Beaufort Scale 0–3 3–5.5 over 5.5

Colón Ridge Equator

hi

i

SURFACE WIND

3,806m (12,487ft)

–C

Tuamotu F racture Zone

on

Tiki Basin

Westerlies

Peru

s

e e Zon actur

30ºN ad North East Tr Doldrums Sou th Trad East es

so on

Rise

e

r sas F

Tua mo Tu tu a m So Isl o Tahiti ciet an tu y Is ds Rid lands ge

ui

u

que Mar

Lo

e idg atea ll Pl pbe m Ca

4,567m (14,984ft)

Marquesas Islands

es erli

SE M

G u a t e ma l a Basin

Pa c i fi c

Norfolk R

Dunedin

Gallego Rise

4,602m (15,099ft)

Wellington

Chatham

Zone

Pitcarn Island

North Island New Zealand South Island Rise

ture

Fr ac gos

n

Penrhyn Basin

Sou the

7,183m e (23,567ft) Tr Tonga es New Hebrid South 10,800m Fi j i (35,435ft) B as i n

Auckland

a alap

(17,885ft)

Samoa Basin

East

Vanuatu Fiji

Manihiki Plateau

one ure Z

est W

n

Puerto Vallarta A mM i d e r i d l e 6,662m ca Tr e(21,858ft) n ch

OCEAN

n Cook Isla Norther nds 5,451m y

Samoa

a

G

Tropic of Cancer

n ia

i

l

for ali

N ort h Fi j i Basin

o

s

s

P

nd

e

Pheonix Islands

ugh

la

sin

Tr o

ract on F pert

Is

Ba

a Nov

6,249m (20,503ft)

ne

PA C I F I C

Clip

Li

s i a

gema s

C Tr ed en r

os h c

t ri s d Ch Ri

all s sh n t ar ou M am Se

C en t ral Pac i fi c B as i n

30ºN

C of lf Gu

s an ts ici n us ou M am Se

ts

Kammu Seamount ts Midway oun m Islands a Se Haw 6,800m Haw aiia n (22,311ft) aiia Isla n R Zone nds idg acture e kai Fr o l o M 834m Honolulu M o u n t a i n(2,736ft) Hawai’i s Zone ture Frac n o i r a Cl

so o

n amou ror Se

r Fracture Zone 7,184m Surveyo (23,571ft) Fracture Zone Mendocino 5,561m 5,999m (18,246ft) (19,683ft) Zone ture M oon Frac y a r Mount less Mur ain s

Seattle Columbia

Cascadia Basin

SE M on

Tu ft s P la in

Antarctic Circumpolar Current

SURFACE CURRENTS

Na zc aR

Empe

Harris Seamount

Peru or Humboldt Current

Vancouver

Island

l Ri apag s e os

Aleutian Islands 7,314m (23,997ft) Aleu t i a n Tr e n c h

South Equatorial Current

East Australia Current

Antar

Gulf of Alaska Alaska Plain

Kodiak Island

(20,021ft)

60ºN

ific

Bristol Bay

Pa c

20m (66ft)

East

Aleutian Bering Sea Basin 6,102m

North Equatorial Current Equatorial Counter Current

Arctic Circle

e Tr e n h c

Ber ing Strait

Gulf of Anadyr

California Current

Kuroshio

ARCTIC OCEAN Anadyr’

Alaska Current

hil

180º

G

u–C

D

THE PACIFIC OCEAN

Bering Sea AREA

THE COLD, STORMY SUBPOLAR SEAS

of the North Pacific are highly productive, supporting a rich fishery. Geologically, the area is dominated by a subduction zone, and the area’s volcanoes and earthquakes pose an ever-present danger.

INFLOWS

PACIFIC OCEAN

Aleutian Trench LENGTH

2,000 miles (3,200 km)

MAXIMUM DEPTH

26,600 ft (8,100 m)

RATE OF CLOSURE

3 in (8 cm) per year

The Bering Sea is bounded to the south by the Aleutian Islands. On the Pacific side of the islands lies the Aleutian Trench, marking where the Pacific Plate is plunging beneath the North American Plate. It is this subduction zone that gives rise to the volcanic arc of islands, the most northerly link in the Pacific Ring of Fire. The trench continues to the east,

SEALS IN THE ALEUTIAN ISLANDS

where the contact is between ocean crust and continental crust. The largest volcanic event of the 20th century was the eruption of Mount Katmai on the Alaskan Peninsula in 1912. This boundary can also produce powerful earthquakes such as the event that destroyed part of Anchorage in 1964.

A

B

20,021 ft (6,102 m)

Pacific Ocean; Yukon, Anadyr’ rivers

The Bering Sea is named after a Danish navigator in the Russian Navy, who explored the area in 1741. It lies between mainland Asia and North America, and is bounded by the Aleutian Islands to the south and linked to the Arctic Ocean in the north by the narrow Bering Strait. There is a flow of cold Arctic water south through this strait, feeding a counterclockwise circulation. The main freshwater input is the Yukon River, which has deposited an extensive delta at its mouth. The Bering Sea is one of the world’s richest fisheries, helping Alaska account THE BERING STRAIT

This satellite image shows ice from the Chukchi Sea streaming south through the Bering Strait.

C

60

˚N

890,000 square miles (2.3 million square km)

MAXIMUM DEPTH

D 170˚E

160˚E

150˚E

E

F

Arctic C

170˚W

ircle

180˚

Chukotskiy Poluostrov

dyr’

Anadyr’

1

R US S I AN F EDER ATI O N

Gulf of Anadyr

Sea of Okhotsk

cha e Mys Kamerrac 7,864m Shipunskiy T (25,802ft)

ge

Rid se

an

170˚E

Tr

en

Rat I sla

Kiska Island Amchitka Island

ch

nds

Pa ss

Ri

ti

Takoma Reef

Am ch itk a

an

l

E m p e r o r Se am o un ts

ti

A

AT L A S O F T H E O C E A N S

eu

B

160˚E

1,857m (6,093ft)

u

11m (36ft) Bowers Bank

idge

Al

A

4

e

Umnak Be Plateau ring Canyon

Islands Tanaga A l e u t i a n Island

Atka Island

Andreanof Islands

20m (66ft)

Atka

D

E

62m (203ft)

Unimak Island False Pass

n

idso Dutch Dav ank Umnak Harbor B Island Unalaska ds Island

Fox

Islan

7,314m 170˚W (23,997ft)

180˚

C

Pribilof Islands

R ers

e

6,088m (19,975ft)

Northwest Pacific Basin

Bowers Attu Attu Near Basin Island Islands Agattu Island

Cape Newenham

w Bo

33m (108ft)

it Kuskokwim Bay

20m (66ft)

Bering Sea 6,102m (20,021ft)

Ulm Bowers Seamount Plateau

Et

Nunivak Island

4,024m (13,203ft)

Ris

r

Komandorskiye Ostrova

ev

Ku

T ile

re

Aleutian Basin

ch

˚N

Mednyy Seamount

ru

50

h nc

Pervenets Canyon

Ostrov Mednyy

Ob

3

635m (2,083ft)

Amukta P ass

Kamchatskiy Zaliv Ostrov Beringa Petropavlovsk- Kronotskiy Kamchatskiy Zaliv a tk

Saint Matthew Island

ov

tk a

Ust’-Kamchatsk

Hooper Bay

sh

c ha

Kamchatka Basin Mys Sivuchiy ir

Kam

29m (95ft)

Mys Olyutorskiy

Sh

P

Olyutorskiy Zaliv

a St r

Ka

ch

a atk

s

12m (39ft)

Norton Sound

in ol

m

2

in en

ula

Saint Lawrence Island

Mys Navarin

Z al iv sky n i rag Ka Ostrov Karaginskiy

Nome Norton Plain

Khatyrka Ossora

Seward Peninsula

Chirikof Basin

Mys Chukotskiy

Good Bayhop

e

Ana

Chukchi Sea Stra it

The Bering Sea And Gulf of Alaska

for about half of the total US fish and shellfish catch. Harbor seals and gray whales also take advantage of these productive waters. In contrast to the deep ocean basin beneath the southwestern half of the sea, the broad continental shelf in the northwest is very shallow. Much of this area formed a land bridge during the last ice age, when sea levels were up to 390 ft (120 m) lower than they are today. This route was ice-free for extended periods, allowing several species, including humans, to migrate from Asia to North America on foot for the first time.

PACIFIC OCEAN D3

Ber ing

458

F

459 PACIFIC OCEAN I3

PACIFIC OCEAN L4

Gulf of Alaska AREA

Cascadia Basin

600,000 sq. miles (1.5 million sq. km)

MAXIMUM DEPTH

AREA

16,400 ft (5,000 m)

66,000 sq. miles (170,000 sq. km)

MAXIMUM DEPTH

Susitna, Copper rivers; icebergs from numerous glaciers

9,600 ft (2,930 m)

Pacific Ocean; Columbia, Fraser rivers

INFLOWS

INFLOWS

A counterclockwise subpolar gyre extends across the north Pacific and into the Gulf of Alaska, fed by the warm waters of the northern Kuroshio Extension, the extension of the Kuroshio Current. The surface waters are cooled and become less saline due to precipitation as they cross the ocean. Many of the storms that lash the west coast of Canada originate in the Gulf of Alaska. The circulation is completed as the Alaska Current and the Aleutian Current return west along the Alaskan coast and south of the Aleutian Islands. The gulf ’s waters are very productive, providing feeding grounds for many species of fish. Pacific salmon spend up to five years at sea, much of it in the gulf and adjacent seas, before returning to spawn in the Asian and North American rivers where they

The Cascadia Basin is the last remnant of the original eastern Pacific oceanic plate, the Farallon Plate, which has been almost entirely subducted beneath North America. The Cascade Range of volcanoes in Oregon and Washington State, including Mount St. Helens, are a product of this subduction. Mount St. Helens erupted in a catastrophic explosion in 1982, killing 57 people, and still shows signs of activity. Earthquakes and associated tsunamis are also a risk in the area, although the last major earthquake is thought to have been in 1700. The underlying ocean crust appears to be split into three small plates. The largest is the Juan de Fuca Plate, named after a Greek sea captain who explored the area for Spain in 1592. The Explorer Plate lies to the north and the Gorda Plate to the south.

G

ALASKAN FJORD

were born. The floor of the Gulf of Alaska is peppered with seamounts. There are two main chains: the Patton and Gilbert seamounts, and the Kodiak Seamounts, both running away from the Alaska Peninsula. Their origin is the Cobb Hotspot, situated beneath the spreading center of the Juan de

H 150˚W

160˚W

Fuca Plate west of Vancouver Island. The seamounts were created above the hotspot over the last 30 million years, then carried northwest by seafloor spreading. Since 1977, oil has been shipped through ports on the south coast of Alaska. In 1989, Prince William Sound was the site of one of the worst maritime environmental disasters, when the tanker Exxon Valdez ran aground, releasing about 30 million gallons (114 million liters) of crude oil.

The valleys and fjords of the Alexander Archipelago testify to extensive erosion by glaciers during the last ice age.

I ircle

Arctic C

J

K

130˚W

140˚W

L

120˚W

110˚W

SCALE 0

0

U N I T E D STAT E S O F A M E R I C A

nR ive r

KEY 200

100

300

100

400

500 km

sea level

300

200

400

500 miles

800 ft (250 m)

˚N

1,600 ft (500 m)

60

1

Yuk o

3,300 ft (1,000 m)

er

9,800 ft (3,000 m)

im R

iv

6,500 ft (2,000 m)

ko

kw

16,400 ft (5,000 m)

s Ku

C A N A D A

Anchorage

K

Inle t Cook

rai t

a

ul

S he li

ns ni

Po r Ba tloc nk k

la

A

o

Gilbert Seamount

Gilber

Parker Seamount

5,267m (17,281ft)

160˚W

G

Gibson Seamount

Miller Seamount White Marsh Seamount

t Se am o

ge oppe Rid

Sch

un

I

e

idg ters R

N

50˚

Ch arl ot t e

Explorer Seamount

ra

Vancouve it of GeVancouver r Islan orgia d Victoria Strait of Seattle Juan de Fuca UNITED STATES OF AMERICA

Pe

ts

766m (2,513ft) 150˚W

H

t (699ft) Cape Bowie St.James Seamount Isla QueenCharlotte n ds Sound Oshawa Cape Seamount Scott

Denson Seamount

Alaska Plain

St

Murray Seamount

Qu

Seamounts

een

ai Str cate He

ag

n

Patton Seamount Patton

140˚W

130˚W

J

K

Cascadia Basin L

4

AT L A S O F T H E O C E A N S

el

ia

en

ch

3

ip

A

t leu

Tr

tectonic plate boundary

rc h

Pe

Gulf of Alaska

A

a

Chichagof Admiralty Island Island A Sitka 3,640m Baranof (11,943ft) Island Ketchikan of Alaska Seamount Provinc f l u Prince of e G Pratt Quinn Seamount Wales Prince Rupert Island n Giacomini Seamount Durgin xorance i Seamount D Seamount K t o Cape En Surveyor Seamdiak Knox Seamount ount Dickins s Seamount Welker 213m 295m (968ft)

Seamount

Port Moller Shumagin Islands

maximum depth on map

er

Kodiak

Kodiak Island

sk

sea depth

Glacier Bay

Sound

nd

t

Juneau

xa

Bristol Bay

fS ko

Shuyak Island

seamount

Yakutat

le

Cape Constantine

ai la en insu Seward n Prince Cape Pe William Saint Elias

Homer

2

land

Cordova

460

A

THE PACIFIC OCEAN

B 120˚E

The Northwestern Pacific

LIKE THE BERING SEA TO THE NORTHEAST,

this part of the Pacific is shaped by subduction at the edge of the Pacific Plate. Volcanoes, earthquakes, and tsunamis present a risk to human life, particularly in the densely populated islands of Japan. PACIFIC OCEAN E4

Sea of Okhotsk AREA

600,000 square miles (1.6 million square km)

MAXIMUM DEPTH

11,063 ft (3,372 m)

INFLOWS Sea of Japan/East Sea; Amur, Uda, Okhota, Penzhina rivers

A subarctic shelf sea, the Sea of Okhotsk is a branch of the northwestern Pacific. It is enclosed to the north by the Asian landmass, bounded to the east by the Kurile

Islands, and linked in the south to the Sea of Japan/East Sea by two narrow straits. Navigation of the sea is restricted by sea ice in the winter, when ice formation on ship hulls also presents a danger to shipping. The southern part of the sea is notorious for its sea fogs throughout the year. The Sea of Okhotsk is very productive, accounting for nearly 70 percent of Russia’s East Asian fish catch. It is home to several endangered species of marine life, including Kurile harbor seals and gray whales. The Okhotsk Plate includes the continental crust of the Kamchatka Peninsula, with its string of volcanoes, and the islands of Sakhalin and Hokkaido. In much of the area, the sea floor is quite shallow, but it is deeper in the Kurile Basin, where the ocean crust has stretched and thinned.

HUMAN IMPACT

OIL EXPLORATION A rush to exploit rich oil and gas deposits on the island of Sakhalin Island started in 1996. The area is now the largest recipient of foreign investment in Russia, and oil production is expanding offshore into the Sea of Okhotsk. The large amount of construction in such a short time has raised concerns about the impact on this wilderness environment, including disturbance of the marine life of the Sea of Okhotsk.

Ice can pose a hazard to shipping from November to June, with its location dependent on winds and ocean currents.

PACIFIC OCEAN F5 AND E8

Kurile and Japan Trenches LENGTH

2,390 miles (3,850 km)

MAXIMUM DEPTH

26,575 ft (8,100 m)

RATE OF CLOSURE

3 in (8 cm) per year

Subduction at the Kurile Trench has produced volcanoes along the Kamchatka Peninsula and the volcanic island arc of the Kuriles. The Kuriles form an almost complete submarine ridge between Hokkaido and Kamchatka, with only two deep water channels from the Pacific into the Sea of Okhotsk. The highest Kurile island

AT L A S O F T H E O C E A N S

AREA

378,000 square miles (978,000 square km)

MAXIMUM DEPTH

12,276 ft (3,743 m)

East China Sea; Tumen, Ishikari, Shinano, Agano, Mogami, Teshio rivers INFLOWS

Circulation within the Sea of Japan (also known as the East Sea) is counterclockwise, with warm water entering from the East China Sea through the Korea Strait. There are rich fishing grounds here and in the north. Squid are among the species sought by Japanese and Korean fishermen, who attract the animals

sea level

1 800 ft (250 m) 1,600 ft (500 m) 3,300 ft (1,000 m) 6,500 ft (2,000 m) 9,800 ft (3,000 m) 16,400 ft (5,000 m)

2

land

sea depth maximum depth on map tectonic plate boundary

3

50˚N

This partly finished pipeline will eventually link offshore oil fields with Sakhalin and mainland Russia.

4

CHINA

men Tu

KURILE ISLAND

3,276m (10,749ft)

40˚N

Large craters, such as the flooded center of this island, form when a volcano’s magma chamber collapses or explodes.

Kimch’aek

NORTH KOREA

PACIFIC OCEAN G6

Northwest Pacific Basin AREA

7 Tonghae

2.4 million square miles (6.3 million square km)

MAXIMUM DEPTH INFLOWS

SOUTH KOREA

21,800 ft (6,650 m)

Bering Sea, Philippine Sea

The Oyashio Current (from the Japanese for “mother stream”) brings cold water south from the Bering Sea, along the western edge of the Northwest Pacific Basin, forming the western arm of the subarctic gyre. Where the Oyashio Current meets the warm waters of the Kuroshio Current (“black stream”) off Japan, there is a productive fishery.

Hungnam

Wonsan

au Plate

Sea of Japan/ East Sea

to the surface at night using powerful lights. The continental shelf is slightly wider on the eastern side than on the western side, and particularly narrow off the coast of Korea. There are three main basins: the Yamato Basin in the east, the Japan Basin in the north, and the Tsushima Basin in the southwest. Between these basins lies the Yamato Ridge, possibly a remnant of the spreading center that opened up the sea. The Sea of Japan/East Sea is a geologically complex basin bisected by the junction between the Okhotsk Plate and the Eurasian Plate. In 1983, a magnitude-7.7 earthquake on the sea floor off northern Honshu triggered a destructive tidal wave that reached a height of 46 ft (14 m) at the coast, killing 107 people in Japan and Korea.

KEY

ean Kor

PACIFIC OCEAN C7

is Atlasov. The islands of Honshu and Hokkaido represent a more mature island arc, where crustal thickening has resulted from prolonged subduction at the Japan Trench and the joining of multiple island arcs. With so much tectonic activity, earthquakes are rampant. A magnitude-8 quake in 1923 killed more than 100,000 people in Tokyo and Yokohama. In 2011, the magnitude-9 Tohoku event, 43 miles (70 km) offshore and 19 miles (30 km) beneath the Japan Trench, thrust the sea bed up by 19-26 ft (6-8 m), triggering a tsunami up to 131 ft (40 m) high (see pp. 462-63).

N

seamount

SUPPLY LINE DANGEROUS SEA ICE

60˚

21m (69ft)

Tsushima

Basin P’ohang Pusan ait Str a e r Ko Tsushima Cheju-do Kitakyushu

8

Fukuoka

Kyushu 130˚E

A

B

C

D

E

130˚E

F

G

Manily Gizhiga

Gizhiginskaya Guba Mys Taygonos

S ak Zalihalinski v y

Chumikan

Mys Yelizavety

Deryugina Basin

Okha

Za liv

Kar ag

ins Pen

ka a

Ust’yevoye PetropavlovskKamchatskiy

Kronotskiy Zaliv Mys Shipunskiy

Mednyy

Ostrov Seamount Beringa

Komandorskiye Ostrova

Al

eu

tia

7,864m (25,802ft)

Ob ruc hev

Ostrov Mednyy

nT ren

Ris e

Sea of Okhotsk

50˚N

Institut

Tatarskiy P

Ostrov Paramushir

Ostrov Sakhalin

1,857m (6,093ft)

i mi e ade Ak k Ris u Na

Poronaysk Mys Terpeniya

h nc

ds

i

s a

B

u e

k

c

6

Muroran

t

40˚N

e

s

e

OCEAN

an

Niigata

7

o

Tre nch

Toyama Trench Sa do R

Sado

PA C I F I C

sk

8,180m (26,673ft)

iy

6,650m (21,819ft)

J Tokyo

Ri

a

Honshu

se

p

JAPAN

Sh

at

8

Shikoku 140˚E

C

D

160˚E

150˚E

E

247m (810ft)

F

G

H

AT L A S O F T H E O C E A N S

idg

w

Aomori

Takuyo-daiichi Seamount Smetanin Seamount 5,310m (17,422ft)

r t h

Erimo Seamount

Oga

Himi

n

Hakodate

Sea of Japan/ East Sea Yamato Seamount 236m (774ft) North Oki Yamato Bank Basin NotoOki hanto Bank e id g h R i Ok roug T Oki

e

P

Otaru

Basin

to ma Ya i d g e R

Z

Kushiro

a

Hokkaido

Toyama Seamount

N

Bogorov Ostrovnoy Seamount Seamount Siberia Japan Seamount

Oki-shoto Waka wansa-

K

Ostrov Iturup

v

Musashi Banks Monbetsu

9,783m (32,098ft)

5

i f i c

Ostrov Kunashir

Urup

r is i l e e Tr e

5m (16ft)

Vladivostok Nakhodka

Nevel’skoye Seamount

597m (1,959ft)

e i l Kuril u r Ostrov Gap K

n

h

La Perouse Strait

Ostrov Simushir

ic

Tat ar Tr ou gh

Terney Lake Khanka

Mys Aniva

l Is

R

Kurile Basin

Svetlaya

Obruchev Seamount

an

3,314m (11,070ft)

6,088m (19,975ft)

8,639m (28,343ft)

Makarov

146m (479ft)

4

ts

Vanino

890m Okeanologii Ozernovskiy (2,920ft) Rise

AleksandrovskSakhalinskiy

roliv

ur Am

3

ch

un mo Sea or per Em

Nikolayevsk-na-Amure

chat

12m (39ft)

Kam chatk

Shantarskiye Ostrova

Kam

Kashevarov Bank

312m (1,024ft)

2

e

Ud

ya sk a

Tinro Rise

Mys Sivuchiy

Ust’-Kamchatsk

Tinro Basin a

Bering Sea

Ridg

Mys Yuzhnyy

Ayan

Kamchatka 635m (2,083ft) Basin

ov

Mys Enkan

Ostrov Karaginskiy

ula

Mys Tolstoy Mys Alevina

b Gu

Ossora

rsh

Okhotsk

Olyutorskiy Mys Olyutorskiy Zaliv Shi

RUSSIAN FEDERATION

Magadan

1

iy

Shelikhova Zaliv

295m (968ft)

ins k

500 miles

400

Kam Zal chat iv ski y

300

200

60˚N

k ay

500 km

ins

100

400

zh

300

Pe n

0

200

100

a G u ba

SCALE 0

461

170˚E

160˚E

150˚E

140˚E

H

TSUNAMI STRIKES JAPAN

A tsunami wave surges ahead and begins to engulf homes on the coast of Natori in Miyagi Prefecture, Honshu, on March 11, 2011.

463

Tohuku Tsunami

Wave height map The map below shows maximum wave heights recorded along the affected coasts of Japan. At one location, the water rose for a short time to an estimated 127 ft (38.9 m) above sea level, but in most of the worst affected areas the rise was 10-40 ft (3-12 m). The waves washed over anti-tsunami seawalls, and the water then surged inland for distances of up to 6 miles (10 km). Over an hour or so, an area of nearly 216 square miles (560 square km) was inundated. The tsunami also traveled across the Pacific, causing significant damage in locations thousands of miles away.

STORY OF THE TSUNAMI EARTHQUAKE HITS HONSHU The magnitude 9.0 earthquake, at around 2:45 pm local time, caused severe damage to roads and buildings in Tohuku and some areas surrounding Tokyo. It also set two oil refineries on fire.

TSUNAMI WAVES APPEAR Within a few minutes, media reports and film footage were showing massive tsunami waves sweeping relentlessly toward the coast of the Tohuku region. WARNINGS GO OUT In Japan’s coastal areas, sirens warn of any approaching tsunami, and signs indicate to where people should evacuate. But this time, the waves were so big that the warnings had a limited impact.

PRELUDE WAVES OVERWHELM COAST

The undersea earthquake and consequent tsunami that hit Japan’s Tohuku region (the northeast part of Honshu, Japan’s largest island) on March 11, 2011, is one of the greatest disasters in human terms ever to hit Japan, and financially the costliest natural disaster ever. As of January 2014, it is reported that the catastrophe killed 15,883 people, with 2,640 missing, and has had an estimated economic cost of US$235 billion. In addition, it has had serious environmental results, due to breakdowns, explosions, and leaks caused at the Fukushima nuclear energy plant. The tsunami resulted from a sudden fracture in Earth’s crust along a fault under the sea floor approximately 43 miles (70 km) off Honshu. This rupture triggered a massive earthquake. As sections of the sea floor suddenly sprang upward by around 20–27 ft (6-8 m), powerful tsunami waves were generated. On reaching the coast, these swept through towns and across fields, roads, and airports, smashing dwellings, vehicles, and boats. When the water later receded, a colossal jumble of debris was dumped on the landscape. Within days, it was apparent that tens of thousands of buildings had been destroyed and hundreds of thousands of people displaced. At the Fukushima plant, three reactors suffered overheating and gas explosions after damage to backup power and containment systems. Subsequently, there were leaks of harmful radioactive materials from the plant into the atmosphere, ocean, and ground around the plant.

TSUNAMI SURGE Within 10–50 minutes of the earthquake, colossal quantities of water were surging through harbors and across fields. FLOTSAM AND JETSAM Buildings and their contents were smashed or lifted up and aggregated into floating islands. Many fires broke out.

CHINA

Tokyo Osaka

Earthquake epicenter

Miyagi

TSUNAMI WAVE HEIGHTS More than 23 ft (7 m) 10–23 ft (3–7 m) 6.5–10 ft (2–3 m) 3.3–6.5 ft (1–2 m) 0–3.3 ft (0–1 m)

AFTERMATH

SOUTH KOREA

Miyako Fukushima nuclear plant

RELIEF OPERATION

To¯hoku region NORTH KOREA

EVACUATION SHELTERS As relief operations began, evacuees were housed in shelters improvised from gymnasia. But with difficulties getting food, water, and medicines to survivors, the Japanese government was faced with huge challenges.

DAMAGED NUCLEAR PLANT At the Fukushima nuclear plant, the tsunami stopped pumps that ran vital cooling systems. This caused explosions and leakages of radioactive material that were still being dealt with in 2014.

AT L A S O F T H E O C E A N S

J A PA N

RUSSIA

D

1,600 ft (500 m) 3,300 ft (1,000 m)

Namp’o

Ye l l o w S e a e

Kyushu Nagasaki

Goto-retto Shanghai

Hangzhou

Great Ya n g t z e B a n k

Na

Kagoshima

4,506m (14,784ft)

h

g

yu uk y R

Ry

s

Da

h

u

id

ge

o

TA IW AN

24m (79ft)

Is

d

e Tr

n

c

Okid

7,460m (24,476ft)

y uk

u

120˚E

A

B

continental shelf off the coast of northern China. Warm water flows through the area from the south, feeding the Pacific’s western boundary current, the Kuroshio Current, which allows the survival of the world’s most northerly colonies of coral in the coastal waters of Japan. The area is vulnerable to cyclones moving in from the southwest.

AT L A S O F T H E O C E A N S

AREA

290,000 square miles (751,000 square km)

MAXIMUM DEPTH INFLOWS

8,912 ft (2,717 m)

South China Sea, Philippine Sea, Yangtze River

The East China Sea is a warm, shallow, productive shelf sea that lies between the Chinese mainland and the Ryukyu Islands. It is linked to the South China Sea through the Taiwan Strait, and to the Sea of Japan through the Korea Strait. In spring and summer the warm Tsushima Current flows north through the Korea Strait, but this is suppressed by northerly winds during winter. The region is

ait o

C

SHALLOW SEAS OVERLIE THE BROAD

East China Sea

Ph i li ppine Se a Rid

Kazanretto

ge

Minami D aito Basin

Rid

ge

0

200

100

0

100

4

300

400

500 km

300

200

also occasionally hit by typhoons (hurricanes) during the summer (see pp. 70–71). The continental shelf beneath the South China Sea extends a long way from shore, partly due to sediments deposited by the Yangtze (Chang Jiang), Asia’s longest river. The Yangtze is navigable by ocean-going ships up to 1,000 miles (1,600 km) inland, and China’s main port, Shanghai, lies at its mouth. Fishing is an important source of income for the region, and the East China Sea is a shipping route between the South China Sea, Japan, and the north Pacific. There are also deposits of natural gas beneath the sea floor of the East China Sea, which China started developing in 2003.

PACIFIC OCEAN B2

Yellow Sea 205,000 square miles (530,000 square km)

MAXIMUM DEPTH

400

500 miles

140˚E

D

AREA

9,157m (30,044ft)

SCALE

130˚E

The East China Sea

PACIFIC OCEAN B3

ito

338 ft (103 m)

Yellow, Yangtze, Liao He, Luan He, Yalu, Han rivers INFLOWS

Enclosed to the north, the Yellow Sea is an extension of the East China Sea, lying between the Chinese coast and the Korean Peninsula. It gets its name from the sand carried in suspension by the waters of the Yellow River (Huang He), the largest inflowing river. The sea is very shallow, and tidal ranges along the Korean side are some of the largest in the world.These strong tides also contribute to the color of the sea by stirring up sediment that has settled on the sea floor. The area around the northernmost bay of Bo Hai is one of the most industrialized in China; Dalian is China’s third-largest port. RYUKYU ISLANDS

The climate of the Ryukyu Islands is subtropical, with many of the islands fringed by coral reefs.

h enc

Naha a n l yu

r Bonin T

Okinawa

ge in Rid Bon shoto sawaraOga h oug a Tr

R

ge

Ry

r

3

wa r

Shantou Taiwan P’enghu Banks Liehtao Kaohsiung

Sakishimashoto Hualien

uk

T

e

4

S an w i Ta

in

a

dg

Xiamen

it tra

Ok

aw

Ri

Senkaku Islands

Shikoku Basin

au

Fuzhou

Rid

AmamiO-shima

al

Wenzhou

–P

East C hina Sea

30˚N

asa

hu

Taizhou

CHINA

ma

us

3

2

9,780m (32,088ft)

Og

Ky

Yakushima

Ningbo

gh

–Ji

30˚N

Tanegashima

n

ou i Tr ka

Iwo

tectonic plate boundary

gtze

Fukuoka

o

Yan

maximum depth on map

Nagoya Osaka

St rai t

a re Ko

Cheju-do

8,130m (26,673ft)

Tokyo

Hiroshima d S ea Kitakyushu Inlan Shikoku Tokushima

1

ch ren Izu T

sea depth

JA PA N

Izu-shot

nh Yu

seamount

Niigata

Honshu

Tsushima

Cheju Strait

Ishinomaki

Sado

ge id h i R ug k O ro iT Ok

Pusan

Da

land

North Oki Bank

Tsushima Basin Okishoto P‘ohang

SOUTH KOREA

Mokp’o 2

Sea o f Ja pa n / 21m E a st Sea (69ft)

K

Inch’on Tonghae

9,800 ft (3,000 m) 16,400 ft (5,000 m)

Pl

i d ge

AN PA C I F I C O C E

6,500 ft (2,000 m)

Wonsan

Korea Bay

n ea u or tea a

Dalian B Haoi hai xia Laizhou r ive Wan wR Yello Yantai Bandai Shandong Qingdao

R Yamato

a n Tr en ch

Bo Hai

Bohai Wan

Kimch’aek Hamhung

40˚N

ur

KOREA

140˚E

Sp

800 ft (250 m)

a lu Dandong Y NORTH

u

sea level

1

130˚E

g Qinhuangdao don ao a n i L W

KEY

F

Sado Ridge

120˚E

E

Iz

40˚N

C

Jap

B

Ya m Ba at sin o

A

464

E

F

PACIFIC OCEAN C4

Ryukyu Trench LENGTH

868 miles (1,398 km)

MAXIMUM DEPTH

24,476 ft (7,460 m)

RATE OF CLOSURE

21/2–3 in (6–8 cm) per year

The Philippine oceanic plate is in contact with the Eurasian Plate to the south of Japan, resulting in a subduction zone marked by the Ryukyu Trench and the Nankai Trough.Volcanic island arcs have resulted to the northwest of the trenches.The Ryukyu Islands are a relatively young island arc compared with the mature arc of the Japanese islands of Honshu and Hokkaido, which has grown to a considerable land mass.The Ryukyu Islands include Okinawa, home to a large American naval base.

THE SOUTH CHINA SEA PACIFIC OCEAN A2

Gulf of Thailand

C

Gulf of Haikou Vinh Tongking Hainan

Kaohsiung

Ba

hi

ne an Ch

11m (36ft)

5,277m (17,314ft)

Dao

6,326m (20,756ft)

at ra

Pangkalpinang 100˚E

A

Pontianak

Pulau Bangka Pulau Belitung 110˚E B

on Luz

e

ppin Phili

M a

Gulf of North Samarinda Makassar Tomini Basin Balikpapan Palu

Banjarmasin

C

KepulauanM Sula o

Banda Sea

PALAU

D

p Ya

3

PACIFIC OCEAN 1,733m (5,686ft)

West Caroline Basin

Ternate

Equator

Halmahera Sea

luc

Ulithi

T

cas

164m Ceram Sea (538ft)

Pulau Buru

120˚E

8,510m (27,920ft)

8,054m (26,425ft)

Pulau Halmahera

Molucca Sea

2

10˚N

Pulau Morotai

Manado

West Mariana Basin

Yap

Celebes Sea Celebes Kepulauan Kepulauan Basin Sangir Talaud 5,499m

Celebes

20˚N

MICRONESIA

Tinaca Point

I N D O N E S I A

Borneo

lf

m

4

Kepulauan Lingga

ch Ar

(18,042ft)

Kuching

She

Equator

Pa la

a

Singapore SINGAPORE

M ALAYSI A

Maka Straissar t

Kra Isthmus of

p

nd

la nsu en i

M A L AYSI A Natuna Sea

Su

Sulu Sea

Kepulauan Natuna

Su

yP al a

of

ala cc a

5,513m (18,088ft)

Panay Kitty Hawk 2m Cebu Leyte 10,057m Seamount Union Spratly (7ft) Cebu (32,997ft) Bohol ea Reefs Islands Negros Palawan lS London ho Reefs Commodore Bo Reef Rifleman 3m h Sulu Mindanao ug Bank (10ft) rait Basin ro bac St Dallas n T Bala Moro o lu g Reef wa Gulf Davao Su ipela Cape San Agustin Kota Kinabalu BRUNEI Bandar Seri Begawan

1

Ambon Pulau Seram

Manokwari Jazirah Doberai

22m (72ft)

New Guinea

130˚E

E

140˚E

F

4

AT L A S O F T H E O C E A N S

M a it Str

M

Kota Bharu Kuala Terengganu Kuantan

Samar

PHILIPPINES

Bank

265m

Tro (869ft) ug h

h

3

Thitu Reefs

2,050m (6.726ft)

Tr e n c

Songkhla

Royalist Bank

South China Sea Mindoro Reed

as in

e

Hô Chi Minh o ish 10˚N Rach Gia al B ks n y Ko Samui Dao Phu Ro Ba Quôc

Manila

pin

Cam Ranh

Gulf of Thailand

South China Basin

20m (66ft)

ilip

2,688m (8,819ft)

CAMBODIA

Blue Ridge Seamount

tr al B

Benham Plateau

Ph

Bangkok Cha-Am

Lexington Seamount

Quy Nhon

Stewart Seamount h Manila Trenc

VIETNAM

o Chraaya Ph

2

d

idg e

Philippine Sea

n Ce

ekong

Da Nang

THAILAND

l fie es k l c c an B

ait oR

l

M

Paracel Islands

Oki d

h enc Ryuk yu Tr

140˚E

88m (289ft)

ge

10m (33ft)

130˚E

7,460m (24,476ft)

ch

LAOS

Hai Phong

s

Tr en

20˚N

Hong Macao Kong ker e s er nk

nd

P realau nc h

200

100

500 miles

400

I sla R y u ky u

s

s

0

300

n

Shantou

Xi Jiang

V

1

100 200 300 400 500 km

TAIWAN

Hualien

Ba

0

120˚E

Xiamen

F

Rid

CHINA

E

ge

110˚E

PEARL-COLLECTING IN THE SULU SEA

Luz o

100˚E SCALE

D

The Sulu Sea is a deep, tropical sea surrounded by islands. Currents follow the monsoon winds, coming from the south in the summer and the north in the winter. Small-scale fishing is the main economic activity in both the Sula Sea and the neighboring Celebes Sea, with shrimp, turtles, and pearl oysters among the catch.

n Rid

B

Ta Ba iwa nk

A

A semi-enclosed extension of the South China Sea, the Gulf of Thailand lies between the Malay Peninsula and Indochina. The gulf contains offshore natural gas, and some oil deposits. Its shallow waters are largely fed by fresh river water inflow, principally from the Chao Phraya River. This river input gives the surface waters a relatively low salinity, while salt water from the main part of the South China Sea only enters deep down, pooling in areas deeper than 160 ft (50 m). Coral reefs thrive in the warm water, and there is a strong tourist industry based around good dive sites, such as the island of Ko Samui. To the south of the island, the Sunda Shelf was a land bridge during the last ice age, connecting Borneo, Sumatra, and Java to the Asian mainland.

18,400 ft (5,600 m)

Celebes Sea

au

The deep central basin of the South China Sea is surrounded by broad continental shelves for the most part. There are oil and natural gas fields in the Gulf of Tongking and the Vereker Banks, and off Borneo and across the Sunda Shelf. The South China Sea is the world’s second busiest sea lane, with at least 25 per cent of the world’s crude oil passing through it. The South China

INFLOWS

sin

16,457 ft (5,016 m)

Xi Jiang, Red, Tha Chin, Mekong rivers

INFLOWS

100,300 square miles (260,000 square km)

MAXIMUM DEPTH

Ba

1.4 million square miles (3.7 million square km)

MAXIMUM DEPTH

AREA

262 ft (80 m)

South China Sea, Chao Phraya River

INFLOWS

Basin is dotted with banks and reefs, which has more than 200 tiny islands. Among these are the uninhabited Spratly Islands, whose ownership is disputed between China,Vietnam, Taiwan, Malaysia, Brunei, and the Philippines. This dispute is motivated by the presence of minerals, and it is estimated that vast oil reserves lie underneath the islands. Typhoons blow in from the Pacific in late summer. Typhoon Haiyan, the strongest to reach land, hit the Philippines in November 2013, with wind speeds over 186 miles (300 km) per hour producing a 16 ft (5 m) storm surge (see pp. 72-73). On reaching Vietnam a few days later, it had weakened into a tropical storm.

South China Sea AREA

MAXIMUM DEPTH

Pal

the five oceans, and its productive waters account for more than eight percent of the world’s fish catch. This tropical sea is fed with water from the Java Sea through the Sunda Strait, which flows weakly north, and out through the Taiwan Strait. The northern part of the area can be battered by typhoons in the late summer.

Sulu Sea

124,000 square miles (320,000 square km)

AREA

hu–

THE SOUTH CHINA SEA IS THE LARGEST

PACIFIC OCEAN C2

PACIFIC OCEAN D3

Kyus

The South China body Sea of water after

465

A

B

C 130˚E

Honshu Nagoya

aS

N

Shanghai

Great Yangtze Bank

30˚N

Tanega-shima Yaku-shima

an

k

h

u

g ds h

Ry ky Ryu

Ok

u

ida

ito

88m (289ft)

Ri

dg

9,157m (30,044ft)

n si

zon

in

9,888m (32,442ft)

pp ili 10,057m (32,997ft)

Yap

Cape San Agustin

P Tr alau en ch

PALAU

Moro Davao Gulf

Molucca Sea

164m (538ft)

o

C eleb es

lu

Halmahera Sea

cca

s Ceram Sea

N

ew

Manokwari Jazirah Doberai

East Caroline Basin

7,249m (23,784ft)

Gu

inea

Tr e n c

Ma

h

New Guinea

130˚E

Manus Island

Lyra Basin

1,402m (4,560ft)

rc hipe

lago

Lyra Reef

Bismarck Sea Wewak

PAP U A N E W G U I N E A Sepik

140˚E

C

n

e n ch u s Tr

Bismarc k A

Jayapura

Pulau Seram

B

1,554m (5,099ft)

22m (72ft)

Ambon

Banda Sea A

1,733m (5,686ft)

I N DO N E SI A Pulau Buru

M I C R O N E S I A

ch

Ternate

Equator

Caroline Ridge Chuuk Islands

4,262m (13,984ft)

Pulau Halmahera

r

D

New Ireland

150˚E Rabaul

E

F

Java Rise tong On

5,499m Manado (18,042ft)

Kepulauan Sula

West Caroline Basin

Pulau Morotai

c

I slan d s

Mussau Tren

Cele be s Ba sin

So ro l Tr eR ou gh ise

olin

4,859m (15,942ft)

Kepulauan Sangir

M

AT L A S O F T H E O C E A N S

Kepulauan Talaud

Celebes Sea

Car

h ug Tro e n aroli West C

Tinaca Point Tinaca Point

Ca roli ne

We st

Ya

ch

8,510m 8,054m (26,425ft) (27,920ft)

pT ren

Tr e n

Mindanao

i

ch

Ulithi 5,513m (18,088ft)

M

Challenger Deep 10,920m (35,829ft)

e

Cebu Leyte Cebu Negros Bohol ea S Sulu ol oh B Sea

10˚N

East Mariana Basin

GUAM

Ph

pin

Panay

ll

nts ou

ilip

Samar

PHILIPPINES

e

6,464m (21,208ft)

m ea

Ph

Mindoro

8

Saipan Tinian

g

S

Manila

7

West Mariana Basin

a

n

265m

in T (869ft) rou gh

NORTHERN MARIANA ISLANDS

M

ch

e

2,050m (6,726ft)

a

Lu

Sea

i a n a Tr e n

5

PAC I F I C Mar

20m (66ft)

1,082m (3,550ft)

na R idge

n Ce

tra lB as

Marcus Island

Maria

Ky us hu –P al au

e

Ph ilippine Benham Plateau

Michelson Ridge

ch

t Ma ri an a Rid ge We s

Luz on Ridge

6,326m (20,756ft)

11m (36ft)

6

Ridge

Choyo Seamount

Ri dge

ch

e

en

g

d

7,460m (24,476ft)

yu

ito

Ba

TAI WA N 4

i

5,661m (18,574ft)

en

uk

hi l Basanne h C 20˚N

R

(79ft)

Sakishimashoto Hualien

Da

Tr

ro

i k Ok yu 24m R

Kazan-retto

Bonin Tr

T a sl w u I a n y Naha

Senkaku Islands

3

Okinawa an

Makarov Seamount

in Ridge Bonawara-shoto Ogas gh ra Trou

Shikoku Basin

Amami-Oshima

Isakov Seamount

a Ogasaw

CHINA

1,339m (4,393ft)

9,780m (32,088ft)

idge ima R

4,506m (14,784ft)

2

East China Sea

ug

u

Iwo–J

Kagoshima

Tr o ai

Iz

I

Nagasaki

Goto-retto

Northwest Pacific Basin

I z u Tr e n c h

Kyushu

ur Izu-shoto

Cheju-do

Sp

6,650m (21,819ft)

8,130m (26,673ft)

Tokyo

Osaka

Hiroshima Sea Kitakyushu land e r n o K Shikoku Tokushima Fukuoka

Cheju Strait

F 150˚E

JAPAN

Pusan

tra it

1

E

140˚E

Sea of Japan/ East Sea

SOUTH P’ohang KOREA

Yellow Sea

D

Eauripik Ris e

466

G

H

I

160˚E

MICRONESIA

467

170˚E

Micronesia

KEY sea level

1 800 ft (250 m) 1,600 ft (500 m)

THE NAME MICRONESIA APPLIES TO AN AREA in the western Pacific, north of the equator. Its stretches to the Caroline and Mariana islands in the west, and Nauru, the Marshall Islands, and Kiribati (or Gilbert) Islands to the east.

3,300 ft (1,000 m)

PACIFIC OCEAN B4

6,500 ft (2,000 m)

247m (810ft)

Philippine Sea

9,800 ft (3,000 m)

2

16,400 ft (5,000 m)

30˚N

AREA

1.9 million square miles (5 million square km)

MAXIMUM DEPTH INFLOWS

land

M

m ap

er ak

S

m ea

o

u

n

seamount

ts

sea depth maximum depth on map tectonic plate boundary

3 73m (240ft)

5,798m (19,023ft)

O C E AN M

id

-

Pa cifi c

20˚N

a

C

rs

6

PACIFIC OCEAN I6

7

KIRIBATI

Gilb

Tarawa

Tu n

er

Melanesian Basin

ga

t

id

g

Banaba

Equator

r

R

u

e

SCALE 100

0

100

160˚E

G

200

300

200

400

8

500 km

300

500 miles

400

170˚E

H

I

TYPE

Coral atoll islands

AREA

70 square miles (180 square km)

NUMBER OF ISLANDS

Bikini were chosen for their remote location as the site of American nuclear bomb tests in the 1940s and 1950s. Several ships were sunk in these tests, but their wrecks are now considered safe for recreational diving.

34

Most of the seamounts scattered across the floor of the western Pacific are far from any plate boundary. The seamounts are found in groups, often strung out in lines running southeast– northwest—the direction of motion of the Pacific Plate. They are caused by hotspots in Earth’s mantle, which periodically punch through the ocean crust to form volcanoes. Some may reach the surface as islands and in the Marshall Islands, coral atolls were formed as the plate moved away from the hot spot and the volcanic islands subsided. The atolls of Enewetak and

GARDEN EELS

These garden eels are among the sea life to be found at the bottom of Rongelap Atoll in the Marshall Islands.

AT L A S O F T H E O C E A N S

a

Marshall Islands

15m (49ft)

s nt ou

i

0

The southern members of the Mariana Islands are limestone platforms with fringing coral reefs.

Majuro Atoll

am

s

NAURU

At the eastern edge of the Philippine Plate lies the volcanic island arc of the Northern Mariana Islands. To the east lies the Mariana Trench, where the Pacific Plate is subducting beneath the Philippine Plate. The Mariana Trench includes Challenger Deep—at

e

in

Kosrae

C

ha

e

11/2 in (4 cm) per year

35,827 ft (10,920 m), this is the deepest known part of the ocean. It was named after a British survey ship that measured its depth in 1951. It was explored for the first time in 1960 by the deep-sea submersible Trieste, followed by remotely operated submarines in 1995-98 and 2009, and by film director James Cameron in Deepsea Challenger in 2012.

MARIANA ISLANDS 10˚N

in

S

lik

h

35,827 ft (10,920 m)

RATE OF CLOSURE

Philippine Basin is the deepest and oldest, separated from the West Mariana Basin by the Kyushu–Palau Ridge. This ridge, and the Iwo-Jima and West Mariana ridges, are the remnants of island arcs associated with ancient subduction zones.

ll

Ra

n

ha

1,580 miles (2,542 km)

MAXIMUM DEPTH

TYPHOON DESTRUCTION

a

Kwajalein Atoll

Pohnpei

5

MARSHALL ISLANDS

ta k Ra

Bikini Atoll

M

o

LENGTH

5,623m (18,499ft)

Enewetak Atoll

PACIFIC OCEAN E5

Mariana Trench

Sea mo un ts

Zubov Seamount

The Philippine Sea stretches east to west between the Marianas Islands and the Philippines, and from north to south between Japan and Palau. This warm sea is swept by the North Equatorial Current, which turns north to form the Kuroshio Current. The water becomes very warm in the summer, and the area is a breeding ground for typhoons. The Philippine Sea is underlain by the Philippine Plate, an oceanic plate that is subducting at the Philippine and Ryukyu trenches. The plate is split into two main basins. The westernmost

4

Wake Island

35,580 ft (10,540 m)

Pacific Ocean, South China Sea

468

THE PACIFIC OCEAN

Midway and Hawaii

Hawaiian Islands

TOCEAN CIRCULATION IS CLOCKWISE

in the central North Pacific, with the Kuroshio Extension flowing eastward in the north, turning south in the east, and returning as the North Equatorial Current south of the Hawaiian Islands. The seafloor is dominated by seamount chains, mostly running from northwest to southeast, and fracture zones, oriented roughly east–west. PACIFIC OCEAN B1

TYPE

TYPE

Coral atoll islands

1,200 miles (2,000 km)

AREA

21/2 square miles (6.2 square km)

NUMBER OF SEAMOUNTS

17

NUMBER OF ISLANDS

The Emperor Seamounts stretch over 1,200 miles (2,000 km) from the northwestern Hawaiian Islands in the south to the Aleutian Trench in the north. They are the oldest part of the Emperor–Hawaii seamount chain—more than 40 million years old—with age and depth increasing to the north. The individual seamounts are named after emperors of Japan.

A

4

These four islands form a coral atoll that lies roughly halfway between North America and Asia. Its position has made it useful for a variety of purposes over the years, first as a telegraph cable and radio station, then as a flying boat stopover, and as an important naval and air station in wartime. Today it is administered by the US government as a wildlife refuge.

B

1,600 ft (500 m) 3,300 ft (1,000 m)

Emperor Seamounts

40˚N

800 ft (250 m)

Fluid, basaltic lava from the Kilauea volcano reaches the Pacific Ocean at Kalapana, Hawaii.

D

E

170˚W

F

r yo ne rvere Zo u S tu ac Fr

160˚W

h oug okTr Chino

rT ro pe

1

19

HAWAIIAN LAVA

180˚

Em

sea level

6,400 square miles (16,600 square km)

C

170˚E KEY

Volcanic islands

AREA

The Hawaiian Islands are a volcanic chain, with large, active volcanic islands at the eastern end, and older, subsided seamounts and atolls at the western end of the chain. They are a continuation of the Emperor seamount chain, created by the same hot spot beneath the sea bed as the Pacific Plate first moved north, and then west-northwest. This change in direction of plate motion about 40 million years ago accounts for the different alignments of the Emperor and Hawaii chains. Hawaii’s Mauna Loa is a broad shield

Midway Islands

Volcanic seamount chain

LENGTH

TYPE

NUMBER OF ISLANDS

PACIFIC OCEAN C3

Emperor Seamounts

volcano, the largest on Earth. From its base on the sea floor it rises about 55,800 ft (17,000 m)—much taller than Mount Everest. Its weight has caused the underlying ocean crust to sag, producing the Hawaiian Trough to the north and east of the main island. The seas around Hawaii are tropical, and warm enough for coral reefs to grow. The prevailing winds in this region are the trade winds from the northeast, making the northeast coasts of the islands considerably wetter and greener.

PACIFIC OCEAN E3

7,184m (23,571ft)

ro ug h

5,547m (18,200ft)

Me

nd

o

Fra

c

e tur

Zo

ss

9,800 ft (3,000 m)

ne

5,999m (19,683ft)

or

w t

ia

ia

e

s

Moro Reef

Ha wai ian

Tropic

Gardner Pinnacles

R er ck e N

-Pac

ific S eamou n

ts

Hawai‘i

0

C

4

100 200 300 400 500 km

0

100

200

300

400

500 miles

160˚W

170˚W

180˚

B

u a Maui gh n Hilo

Honolulu Lana‘i

SCALE

Johnston Atoll

A

3

i

g id

834m (2,736ft)

Wake Island 170˚E

cer

of Can

a Tern Necker Isla lok one Ha Moure Z nds w a i Island Island t c ian ra HaF R i d Nihoa Kaua‘i O‘ahu ge Moloka‘i Tro wai 20˚N i e

20˚N

4

c

ne

5,999m (19,683ft)

nt

dg

Laysan Island

6,798m (19,023ft)

Mid

Fr a

Zo

150˚W

ou

Ri

Lisianski Island

M

y u rr a

e tur

am

n

56m (184ft)

OCEAN

Se

ai

73m (240ft) of Ca ncer

aw

Midway Islands Pearl and Hermes Reef

Kure Atoll

5,800m (22,311ft)

ns

H

PAC I F I C

tectonic plate boundary

30˚N

us ic

es

sea depth

AT L A S O F T H E O C E A N S

M

th

18m (59ft)

30˚N

maximum depth on map

Tropic

2

N

Mellish Seamount

Kammu Seamount

land seamount

3

1

Ri se

16,400 ft (5,000 m)

2

40˚N

He

6,500 ft (2,000 m)

o cin

150˚W

D

E

F

C

140˚W

Mend

Eureka

Fr a c t ur e Z o ne Delgada Fan

Zone

100˚W

0

100 200 300 400 500 km

0

100

Monterey

Erben Tablemount

Los Angeles San Diego Tijuana

2

en t

B

aj

1,468m nt ai (4,817ft) ns

ul f

o

if

f

or

C

ni

al

MEXICO

a

d Ce

ifo

rn

ro

sT re nc La Paz h Cabo San Lucas

OCEAN

M olo k ai Fracture Zone

Guaymas

G

al

516m (1,693ft)

ncer

C

PA C I F I C of Ca

a

Isla Cedros Punta Eugenia

Isla Guadalupe

Tropic

30˚N

m rp ca Es

M ou

Fieberling Tablemount

n tto Pa

2

3 20˚N

ia

Tropic

28m (92ft)

Revillagigedo Islands Alphecca Seamount

ture Zone Clarion Frac

Mazatlán 3

Frac ture Zon e

Mathematicians Seamounts

130˚W

B

120˚W

THE CALIFORNIA CURRENT FLOWS

south in the western North Pacific, forming the western arm of the North Pacific Gyre. South of the Tropic of Cancer it sweeps west to become the North Equatorial Current. Against the California coast, a cold coastal current runs north. The floor of the western Pacific slopes gently away from North America, scarred by long fracture zones. PACIFIC OCEAN C1

4

1,600 square miles (4,160 square km) 1,970 ft (600 m)

San Joaquin, Sacramento rivers

THE GOLDEN GATE BRIDGE

D

E

F

PACIFIC OCEAN C1

Monterey Bay AREA

620 square miles (1,600 square km)

MAXIMUM DEPTH INFLOWS

10,700 ft (3,250 m)

Pacific Ocean

Monterey Bay is one of the most diverse marine ecosystems in the world, and is home to a variety of fish, invertebrate, seabird, and mammal species, including sea otters, harbor and elephant seals, bottlenose dolphins, and turtles. It is also famous for its fish-processing industry, which grew up in the early part of the 20th century around Cannery Row. The bay is the site of one of the longest undersea canyons in the world, Monterey Canyon, which reaches a depth of more than 9,800 ft (3,000 m) and runs 60 miles (100 km) offshore. A mud volcano north of the canyon is the source of cold hydrocarbon seeps (see pp.188–89), which support an ecosystem based on metabolizing sulfide compounds, rather than using sunlight for energy. Similar deep-sea communities are found at hydrothermal vents on the mid-ocean ridges.

PACIFIC OCEAN E2

Gulf of California AREA

62,000 square miles (160,000 square km)

MAXIMUM DEPTH INFLOWS

10,000 ft (3,050 m)

Fuerte, Sonora, Yaqui, Colorado rivers

The Gulf of California was originally named the Sea of Cortez by Spanish explorers and is still known locally by that name. It marks the boundary between the North American and Pacific plates. The peninsula of Baja California lies on the Pacific Plate and is moving northwest, away from Mexico, at about 2 in (5 cm) each year. To the north, large earthquakes are quite frequent along the San Andreas Fault. The waters of the gulf support a rich ecosystem and a healthy commercial fishery. In addition to the native species, migratory visitors include humpback whales, manta rays, and leatherback turtles. The California gray whale completes the longest migration of any mammal, spending a few weeks each year in breeding grounds off Baja California, before returning to the Bering Sea, 5,000 miles (8,000 km) away.

AT L A S O F T H E O C E A N S

San Francisco Bay

San Francisco Bay and its associated water bodies form the world’s largest natural harbor. In addition to San Francisco itself, there are major ports in Oakland, Richmond, Stockton, Sacramento, and San Pablo Bay. The bay is an estuary, containing large areas of salt marsh that support a number of endangered species. It is famous for its sea fogs, which arise when sea breezes blow over cold inshore waters.

110˚W

C

Gulf of California

INFLOWS

ture Orozco Frac Zone

st e Ea Ris ic cif

140˚W

MAXIMUM DEPTH

Mid A m dle e Tr e nr i c a ch

Khayyam Seamount

457m (1,499ft)

AREA

20˚N

Pa

4

River a

Clarion Island

Shimada Seamount

ncer

of Ca

Puerto Vallarta

A

1

500 miles

400

Channel Islands

M u rr a y F r a c t u r e Z o n e Mo on les s

300

200

U N I T E D STAT E S OF AMERICA

Monterey Fan

30˚N

469

SCALE

San Francisco

5,561m (18,246ft)

F

110˚W

120˚W

nto

e r Fr ac ture

E

Sacrame

Pione

1

130˚W

ocino

D

do

B

Co lora

A

GREEN SAND BEACH

Papakolea or Mahana Beach, on the volcanic Big Island of Hawaii, is one of only a handful of beaches in the world composed of predominantly green-colored sand. The distinctive hue comes from the mineral olivine, eroded from rocks in the volcanic cinder cone that partly encircles the beach.

472

THE PACIFIC OCEAN

Melanesia

PACIFIC OCEAN F1

Bismarck Sea

THE NAME MELANESIA COMES FROM THE GREEK

for “black islands.” The area includes the islands north of Australia, from Celebes and New Guinea in the west, to Fiji and Samoa in the east. The surrounding seas are tropical, their warm waters fed by the westward flow of the South Equatorial Current. The region is geologically complex, with some parts volcanically active. the Solomon Sea appears to consist of one or two very small tectonic plates (microplates) of oceanic origin. The Solomon Sea Microplate is spreading from the area of the Pockington Trough and rotating clockwise, subducting to the north and possibly to the southwest.Volcanic activity is particularly intense off the New Georgia Islands, where the spreading ridge is being subducted: the submarine volcano Kavachi breached the surface explosively in 2002. On the other side of the sea, the tectonic upheavals have resulted in uplift of New Guinea’s Huon Peninsula, where raised coral terraces are found some distance inland.

PACIFIC OCEAN F2

Solomon Sea 278,000 square miles (720,000 square km) 29,300 ft (8,940 m)

Pacific Ocean, Coral Sea

INFLOWS

The Solomon Sea lies between the Solomon Islands and the island of New Guinea, with the island of New Britain to the north and the Louisiade Archipelago to the south. The area is geologically complex, forming the remains of a closing ocean basin caught between the Australian Plate moving north and the Pacific Plate moving west. The floor of A Equator

B

Manokwari Jazirah Doberai

Flores Basin

EAST TIMOR Savu Basin

ough r Tr o m Ti

T i m or

Palau Sumba Savu Sea 10˚S

S

ul ah

hu

N e w G u i n e a PAPUA NEW GUINEA

Rabaul

lf he S l

New Britain Lae

A r nhem Land

Groote Eylandt

Gulf of Carpentaria

Sir Edward Pellew Group

Cape York Peninsula

Coral Sea Basin Que en

200

ea Coral Sea Islands

r

R

ee

f

AUSTRALIA Townsville

100

dP lat

3m (10ft)

Whitsunday Group

SCALE 0

slan

u

Cairns

Derby Broome

el f

Papua Plateau

Cooktown

20˚S

4

Port D‘Entrecasteax Moresby Islands

G

Wellesley Islands

Sh ley

300

400

500 km

Mackay 0

100

200

300

400

500 miles

120˚E

A

130˚E

B

140˚E

C

D

ch

1,337m (4,387ft)

Cape Arnhem

Joseph Bonaparte Gulf

n Tre

Solomon Sea

Cape York

Wessel Islands

Bathurst Island

New Britain

Tor res Strait

Darwin Cape Londonderry

Madang

Gulf of Papua

Arafura Shelf Melville Island

Umboi Island

Fly

Pulau Yos Sudarso

Rowley Shoals

Row

New Ireland

Wewak

ie a rr at B

Sa

3

Bismarck Sea

Sepik

re

INDIAN OCEAN

s nk Ba

Timor Sea

h Trenc

Manus Island

Jayapura

Kepulauan Aru

Arafura Sea

Dili

Flores

150˚E n us Ma

am beramo

Kepulauan Kai Kepulauan Tanimbar

Pulau Kepulauan Wetar Damar

F

140˚E

Tre nc h

22m Su (72ft)

Ambon

Banda Sea

Lesser Sunda Islands

AT L A S O F T H E O C E A N S

uinea

INDONESIA

Bone Basin

Sumbawa

Ne w G

E

iM

Pulau Buru

Flores Sea

2

D

Pulau Seram

Teluk Bone

Makassar

c

cas 164m (538ft) Ceram Sea

C ele b e s

The sudden eruption of the Rabaul caldera on the coast of New Britain forced the evacuation of the nearby city Rabaul in 1994.

ng a

Makassar Strai t

1

lu

130˚E Pulau Halmahera Halmahera Sea

o

Palu

M

Molucca Sea Kepulauan Sula

9,200 ft (2,800 m)

Pacific Ocean, Solomon Sea

The Bismarck Sea lies off the north coast of New Guinea. It is surrounded by volcanic islands, the largest being New Britain. The underlying Bismarck Microplate is caught between the Australian Plate, moving north, and the Pacific and Caroline plates, moving west. The northern islands of the archipelago arise from the subduction of the Caroline and Pacific plates, marked by the Manus Trench to the north.Volcanoes on the south side of the sea are currently more active, arising from the subduction of the Solomon Sea Microplate at the New Britain Trench. To the east of the Bismarck Sea lies the Ontong Java Rise. This submarine plateau is one of the world’s largest expanses of igneous rock. It is composed of flood basalts, some of which date back to 120 million years ago.

RABAUL VOLCANO

C

120˚E

Gulf of Tomini

INFLOWS

ngai Digul

MAXIMUM DEPTH

124,000 square miles (320,000 square km)

MAXIMUM DEPTH

Su

AREA

AREA

150˚E

E

F

MELANESIA PACIFIC OCEAN C2

PACIFIC OCEAN K3

Arafura Sea

Fiji Plateau

251,000 square miles (650,000 square km)

AVERAGE DEPTH

Coral Sea, Timor Sea, Banda Sea

GREAT BARRIER REEF

PACIFIC OCEAN G3

The largest coral reef structure in the world, the Great Barrier Reef stretches for more than 1,200 miles (2,000 km).

Coral Sea AREA

1.8 million square miles (4.8 million square km)

MAXIMUM DEPTH

30,070 ft (9,165 m)

West Central Pacific Ocean; Fly, Purari, Kikori rivers

INFLOWS

This tropical sea earns its name from the presence of coral reefs along most of its coasts. The Great Barrier Reef (see p.161) grows out to the edge of the Australian continental shelf, on the western side of the sea. Warm water enters from the Pacific, circulating weakly before leaving through the Torres Strait to the west, or to the

SUNSET OVER THE ARAFURA SEA

G

H

I

J

160˚E

Banaba

Ri d

Ontong Java Rise

M

gh

n

Malaita

Santa Cruz Islands

i

9,175m (30,103ft)

Tre n

10˚S

maximum depth on map tectonic plate boundary

Hazel Holme Bank Pandora Bank

Îles Wallis

Banks Islands

ni

160˚E

H

4m (13ft)

Tanna

Lau Basin Vava’u Group

h

nc re T es rid eb

dg e

Is

Ri

r nte Hu H w Ne

7,183m (23,567ft) 170˚E

I

Koro Sea

J

South Fiji Basin

180˚

K

TONGA Tongatapu Group

10,587m (34,736ft) 10,800m (35,435ft)

L

20˚S

4

AT L A S O F T H E O C E A N S

o ed

aT ro ug h Nouméa

FIJI Suva Viti Levu

roup

l Ca

16m (52ft)

222m Erromango (728ft)

s ch nd en la

w Ne

oya lt y

North Fiji Basin

uG

Tr des ebri N ew H

Efate Port- Vila

3

La

Vanua Levu Fiji Plateau

VANUATU

Bellona Plateau

SAMOA

AND FUTUNA Zephyr Reef

Maewo Pentecost Malekula

NEW CALEDONIA L

Savai’i Apia Upolu

Île Futuna WALLIS

Espiritu Santo

Mellish Rise

sea depth

ch

a

1,577m (5,174ft)

2

land seamount

ya z

s

Santa Cruz Basin

16,400 ft (5,000 m)

VA LU Funafuti

e

Coral Sea

G

3,300 ft (1,000 m) 6,500 ft (2,000 m) 9,800 ft (3,000 m)

U

a

Honiara Guadalcanal Sou San Cristobal th 8.322m So lom (27,304ft) on T rench Rennell

Louisiade Plateau

1,600 ft (500 m)

t

u

l

1

800 ft (250 m)

6,249m (20,503ft)

Vi

o Tr

sea level

KIRIBATI

ge

PA C I F I C O C E A N

e

ew h th N Nor es Trenc brid He

n gto Pockin

KEY

ru

T

nd ds

Bougainville Choiseul 7m Island (23ft) Santa N Newew Ge Isabel Geo orgi 399m rgia a S o (1,309ft) Isla u n

Louisiade Archipelago

Equator

3,179m (10,430ft)

SOLOMON ISLANDS

Solomon Basin

L

180˚

a ng Tu t er lb Gi

NAURU

8,940m (29,332ft)

K

170˚E

Lyra Reef

Buka Island

south as the East Australia Current. The eastern and northern sides of the Coral Sea are marked by deep trenches, where the oceanic part of the Australian Plate is subducting. Volcanism has resulted in the Solomon Islands and the Vanuatu chain. Explosive eruptions in these islands can create pumice, a volcanic rock that floats due to gas bubbles trapped inside. Lumps of pumice are sometimes washed up on the western shore of the Coral Sea.

The Fiji Plateau is the thickest part of the Fiji Plate. The islands of Fiji were originally part of a continuous volcanic island arc alongside Vanuatu and the Solomons. They were moved east when the Pacific Plate changed its direction of motion, triggering the creation of new ocean crust in the North Fiji Basin. The Hunter Ridge to the south marks the transform fracture that allowed this eastward motion, while the Vityaz Trench to the north marks the subduction zone that created the islands, though the trench is now inactive. Over time a substantial platform of limestone accumulated around the original volcanic islands, as they were uplifted, faulted, and folded by the opening of the young, buoyant North Fiji Basin. Growth of the platform continues today, thanks to the coral reefs that fringe Fiji’s hundreds of islands.

nch

Lying over a shallow continental shelf, the Arafura Sea marks the boundary between the Pacific and Indian oceans. During the Indian summer monsoon, water flows westward into the Indian Ocean, pulled by the South Equatorial Current, but the flow is reversed when the Equatorial Counter Current is active during the Indian winter.

Less than 820 ft (250 m)

ga T re

INFLOWS

30,900 square miles (80,000 square km)

AREA

260 ft (80 m)

Ton ga Rid ge To n

MAXIMUM DEPTH

Lau Ridge

AREA

473

CLOSE ENCOUNTER

A hawksbill turtle swims past a group of scuba divers in the Ras Mohammed protected area near the popular Red Sea diving resort of Sharm el-Sheikh, Egypt.

475

Diving Tourism

The Divers’ Code

WRECKS It is not just the living world that attracts divers. In some parts of the ocean, such as here in the Caribbean, the sea floor is littered with wrecked ships. Exploring the hulks can be like traveling back in time.

DIVE SITES

REEFS Coral reefs provide some of the most spectacular sights on Earth. A healthy reef positively teems with a wide variety of wildlife, including many brightly colored fish species, such as these raccoon butterflyfish on a reef in Hawaii. ECOTOURISM Some conservation-minded divers spend their vacations assisting scientists in their research of coral reefs. LOCAL ECONOMIES Residents of prime dive locations can benefit by offering diving services. But if a location becomes too popular, the sheer number of visitors can cause severe damage to the reefs.

FEEDING SHARKS The feeding of top predators, such as this Caribbean reef shark, is a complex issue. Although the behavior of the sharks is altered by such activities, such diving trips are becoming increasingly popular in many locations, resulting indirectly in the protection of the sharks by local operators.

INTERACTING WITH WILDLIFE

divers how to respond if they lose their mask. Hand signals are used to communicate underwater.

BAD PRACTICE A boy diving in the Red Sea touches a spiny pufferfish, causing it to inflate. The handling of marine wildlife can harm both the animal and the diver and is discouraged by the Divers’ Code.

AT L A S O F T H E O C E A N S

The vast majority of modern dive operations and tourist authorities insist on a strict set of guidelines to minimize the effect of too many divers on reefs. The Divers’ Code includes the following points: no contact with coral; maintain buoyancy control so that accidental contact with the reef is avoided; no collection of shells, coral, or other mementos; no touching, harassing, or feeding of any marine animals; and an exclusion zone is to be maintained SAFETY FIRST around large marine A dive instructor teaches novice animals, such as whales.

DIVING ACTIVITIES

BENEFITS AND DRAWBACKS

The pioneering work in 1943 of French divers Jacques Cousteau and Emile Gagnan in creating scuba (self-contained underwater breathing apparatus) moved diving away from being the domain of the military, scientists, and a privileged few and opened up the wonders of the underwater world to a wider public. Although there is an element of risk—diving is still classed as an extreme sport by many insurance companies—a vast array of training agencies and courses exist to assist the potential diver in taking up the sport safely. In line with the increased accessibility of diving and a burgeoning interest in the marine environment, dive operations have sprung up in every location where there is a combination of a tourist market and easy access to a body of water suitable for scuba diving. In the US alone, the number of active divers is estimated to be 1–3 million. The modern diver is faced with a bewildering array of choices when it comes to the dive experience itself. The simplest form of diving is a course that is based within a resort, which supplies all of the equipment and training, and guides the diver around local sites. More specialized is the dedicated dive vacation, where the qualified diver seeks out a location specifically to explore local attractions. Some diving enthusiasts choose to base themselves on dive vessels that explore some of the more remote locations of the undersea world. For the most committed divers, it is possible to join a dedicated diving expedition organization, during which conservation or surveying work may be undertaken at a remote location for a few weeks or even several months.

A

476

B

C

180˚

D

170˚W

E

160˚W

F

150˚W

1 10˚N

C

5m (16ft)

h

ri s tm

n la el e s

M ag Ri

s

5,582m (18,345ft)

R

g e

Kingman Reef Palmyra Atoll Teraina

id

2

a

Central Pacific Basin

Clipp

Tabuaeran

ac n Fr e rt o

ture

Kiritimati Howland Island

K I R I B AT I

Baker Island

3

va No

27m (89ft)

gh Trou

L

Equator

PAC I F I C

i

Jarvis Island

n

6,249m (20,503ft)

Kanton

e

P ho e n i x Is l a n d s Enderbury Island

Malden Island

Orona

Gal

P

gos apa

Frac

ture

Starbuck Island

I

Île Futuna

idge

Tonga R

Ton ga T renc h

Lau Ri dge

Tren ch

FRENCH POLYNESIA

ds

am

otu

ot

u

3,780m (12,402ft)

5,901m (19,361ft)

10,800m (35,435ft)

Île

Tomaszeski Seamount

s

Au

st

ra

President Thiers Seamount

le

s

Southwest Pacific Basin

4,602m (15,099ft)

idg eR

e

Ker mad ec

h Fiji Basin

Sout

an

am

Mangaia

vill

A

Co ok I sland s

Isl

uis

10,047m (32,964ft) 180˚

Atia

ty

Tahiti

Rarotonga

1,039m (3,409ft)

30˚S

Aitutaki

cie

Moorea Papeete

Tu

Lo

AT L A S O F T H E O C E A N S

Tongatapu Group

Ozbourn Seamount

Kermadec Islands

8

10,587m (34,736ft)

a

Lau Basin

So uth er n

NIUE

Tu

ty R idge

Bora-Bora

So

Palmerston

Vava’u Group

Socie

COOK ISLANDS

Samoa Basin

Group 4m (13ft)

20˚S

7

AMERICAN SAMOA

TONGA

Penrhyn Basin

Tutuila

u La

6

e

Upolu

FIJI

Suva Koro Sea Viti Levu

Millennium Island

Flint Island

Suwarrow

Apia

4,370m (14,338ft)

i

Vanua Levu

Manihiki ds Plateau Islan k o o rn C Northe

SAMOA Savai’i

WALLIS AND FUTUNA Zephyr Bank

n

Manihiki

Pukapuka Nassau

Vostok Island

s

Îles Wallis

Rakahanga

s

e id g

5

Penrhyn

Fakaofo Atoll

d

ie R Robb

y

TOKELAU

Nukunonu Atoll 10˚S

5,451m (17,885ft)

n

Funafuti

l

a

Atafu Atoll

l

TUVALU

s

o

4

B

5,655m (18,554ft) 170˚W

160˚W

C

150˚W

D

E

F

G

H

140˚W

I

POLYNESIA

130˚W

Polynesia

KEY sea level

1 800 ft (250 m)

10˚N

1,600 ft (500 m) 3,300 ft (1,000 m) 6,500 ft (2,000 m)

THE FLOOR OF THE SOUTHWEST PACIFIC is dotted with chains of islands and seamounts, and cut by major fracture zones. Its deepest part lies in the Tonga Trench, where the Pacific Plate is subducting beneath the Australian Plate. The counterclockwise South Pacific Gyre controls the ocean currents, with eastward Equatorial Countercurrents north and south of the equator.

9,800 ft (3,000 m)

1,920m (6,300ft)

Zone

PACIFIC OCEAN G4

2

16,400 ft (5,000 m)

land

Marquesas Islands TYPE

Volcanic islands

AREA

490 square miles (1,270 square km)

seamount NUMBER OF ISLANDS

sea depth maximum depth on map tectonic plate boundary

Equator

3

O C E A N Zon

e

4,567m (14,984ft)

PACIFIC OCEAN D5

Cook Islands

M ar

sI esa

q Nuku u Hiva

nds sla

Hiva Oa

Marqu

esas

ure Fract

Zone

10˚S

5

Tiki Basin Tu a m o t u F ractu

la

Ri

nd

Volcanic islands

AREA

93 square miles (240 square km) 15

The Cook Islands are split into two groups: the low-lying coral atolls of the northern group, most of which rise from the Manihiki Plateau; and the mainly high volcanic islands in the south. The largest island, Rarotonga,

re Z one

s

dg

TYPE

NUMBER OF ISLANDS

Despite this isolation, the islands suffered the effects of an earthquake in Alaska in 1946 when they were hit by the resultant tsunami, which rose up to 40 ft (12 m) high in some places.

15

The Marquesas Islands are volcanic in origin, overlying a mantle hotspot, with high mountain peaks and ridges. They lie in the path of the strong South Equatorial Current, flowing from the east, producing eroded coastlines, with steep cliffs dotted with sea caves. Coral reefs are limited to a few sheltered bays. The Marquesas lie farther from a continental landmass than any other island group on Earth.

4

Is

477

ERODED VOLCANIC COASTLINE

rises 2,140 ft (652 m) above sea level and 14,800 ft (4,500 m) above the ocean floor. The islands were settled in about 300 bc by people originating from eastern Melanesia, who migrated via Fiji, Tonga, and Samoa. Polynesians were expert ocean explorers and perfected the use of many navigation aids at a time when European mariners relied on keeping the land in sight. Their techniques included using the stars; knowledge of currents, winds, and wave patterns; and the flight of birds. Captain James Cook was the first European to sight the Cook Islands in 1773. Russian sailors named the islands in his honor in the 19th century.

6

e

A Îles Gam bie

al ustr

RAROTONGA

e ure Zon Fract

Like most of the Southern Cook Islands, Rarotonga has a fringing coral reef several hundred yards offshore, which protects a shallow lagoon and coastal plain.

20˚S

r

Henderson Island

Pitcairn Island

7 PACIFIC OCEAN F6

Ducie Island

Tuamotu Islands

PITCAIRN ISLANDS

TYPE

Coral atoll islands

AREA

340 square miles (885 square km)

NUMBER OF ISLANDS

25m (82ft)

SCALE 0

100

8

200 300 400 500 km

30˚S 0

140˚W

100

200

300

500 miles

400

130˚W

G

H

I

78

The Tuamotu Islands are the longest chain of coral atolls in the world, stretching over 1,200 miles (2,000 km). The Tuamotus were settled by Polynesians by ad 700. Ferdinand Magellan was the first European to chart the group in 1521. The islands became known for their rare black

pearls, and these still form a major part of the economy. The Tuamotu Islands are part of French Polynesia and the islands of Mururoa and Fantgataufa were used as sites for about 200 French nuclear weapon tests between 1966 and 1996. The atolls were formed as volcanic islands subsided, leaving behind their fringing coral reefs. The islands rise from the Tuamotu Ridge, a plateau of volcanic material formed about 63–40 million years ago. The Gambier Islands at the southeast end of the ridge are younger, with their volcanic peaks still standing above sea level.

AT L A S O F T H E O C E A N S

Oeno Island

100˚W ne

dd

Ame

NICARAGUA

ch

COSTA RICA

3,281m (10,765ft)

Panama

o oc

Colón Ridge

OCEAN

1,516m (4,974ft)

Isla Isabela

seamount

maximum depth on map tectonic plate boundary

110˚W

A

C

Galápagos Islands THE EQUATORIAL COUNTERCURRENT

flows into the eastern equatorial Pacific from the west, feeding a counterclockwise gyre over the Guatemala Basin. From the south, the Humboldt Current feeds into the South Equatorial Current, which runs westward across the Pacific. The area is underlain by two plates, the Cocos and Nazca, which are remnants of the original eastern Pacific plate.

AT L A S O F T H E O C E A N S

PACIFIC OCEAN B2

East Pacific Rise LENGTH

5,600 miles (9,000 km)

HEIGHT ABOVE SEA FLOOR RATE OF SPREAD

PACIFIC OCEAN C1

Middle America Trench

3,280 ft (1,000 m)

41/2–6 in (11–15 cm) per year

The East Pacific Rise is the fastestspreading mid-ocean ridge in the world, producing a broad, gently-sloping ridge with few transform offsets. It was here that the first submarine hydrothermal vents, or black smokers (see p.188-89), were discovered. These vents give rise to oases of life on the deep-ocean floor, supporting complex communities of tube worms, clams, shrimp, and crabs, fueled by nutrients in the vent fluids.

LENGTH

G

90˚W

B

1,700 miles (2,750 km)

MAXIMUM DEPTH

21,858 ft (6,662 m)

RATE OF CLOSURE

31/2 in (9 cm) per year

The Cocos Plate is subducting beneath the North American and Caribbean plates at the Middle America Trench. A chain of volcanoes has arisen along Central America’s western coast, with volcanism most active in the southern part of the subduction zone behind the trench. Earthquakes in the area are triggered by plate movement.

D

PACIFIC OCEAN D3

Galápagos Islands TYPE

Volcanic islands

AREA

3,030 square miles (7,850 square km)

NUMBER OF ISLANDS

Manta

Carnegie Ridge

58m (190ft)

Que Fractur brada e Zone F r a c t uG o f a r re Zon e 100˚W

3

COLOMBIA Tumaco

Esmeraldas

Isla San Salvador Isla Santa Cruz Isla San Cristóbal

sea depth

4

Buenaventura

Basin

Galapagos Islands Isla Fernandina

land

3,669m (12,038ft)

Co lom bia

R

s

C

Equator

Panama City Panama

Isla del Coco

9,800 ft (3,000 m)

2

PANAMA Gulf of

3,806m (12,487ft)

6,500 ft (2,000 m)

16,400 ft (5,000 m)

Panama Canal

9m (30ft)

PAC I F I C

3,300 ft (1,000 m)

10˚N

Puntarenas

ge

1,600 ft (500 m)

1

500 miles

400

Caribbean Sea

id

800 ft (250 m)

3

en

500 km

300

200

EL SALVADOR

e Ris

sea level

Siqueiros Fracture Zone

100

400

La Libertad

Guatemala Basin

ific

KEY

6,662m (21,858ft)T r

c 4,217m pe (13,836ft) te

Pac

Torres Seamount

300

HONDURAS

ca

Ri dg e

an hu Te

East

Clipperton

ri

200

100

0

Gulf of Tehuantepec GUATEMALA

Khayyam Seamount

134m (440ft)

0

Salina Cruz

le

ne O ‘G Zo orman Fracture

SCALE BELIZE

Panama Fracture Zone

a Orozco Fr

Mi

re ctu

F 80˚W

MEXICO

e

Zo n

1

E

90˚W

Acapulco

2

D

ch

Frac Rivera ture Zo

C

19

The Galápagos Islands first appeared on maps drawn by Flemish cartographers Abraham Ortelius and Gerardus Mercator in 1570. The Galápagos take their name from the old Spanish word for tortoise, as early visitors found giant tortoises roaming the islands. There are many other species that have made unique adaptations to the local environment, including the marine iguana. It is the only iguana to feed in the sea, diving up to 50 ft (15 m) to forage for marine algae. The cold waters of the Humboldt Current allow Galápagos penguins to survive at the equator. The islands are the result of volcanic eruptions above a mantle hotspot. The same hotspot is

ge Rid a lv rija

Peru–Ch ile Tre n

110˚W

B

nT ren ch

A

478

Equator

ECUADOR

Guayaquil

Gulf of Guayaquil Machala

4

PERU

Tumbes 80˚W

E

F

responsible for driving the Cocos and Nazca plates apart at the Colon Ridge. The Nazca Plate on which the islands sit is moving eastward, so the oldest of the islands are found in the east. They have been volcanically extinct for several million years, but some of the younger islands are still active volcanoes. Farther east, the submarine Carnegie Ridge is also built from Galápagos Hotspot material. GALÁPAGOS ISLAND IGUANA

Study of the islands’ unique animals, including marine iguanas, helped British naturalist Charles Darwin to formulate his theory of evolution.

EASTER ISLAND

Easter Island

Easter Island

the cold Humboldt Current flows north up the coast of South America, forming the eastern arm of the South Pacific Gyre. It then turns west in the tropics, feeding the South Equatorial Current. In some years, this current is weakened and warm water pools in the east, disrupting weather patterns over a wide area of the Pacific Ocean.

Peru-Chile Trench 3,650 miles (5,900 km)

MAXIMUM DEPTH

26,474 ft (8,069 m)

RATE OF CLOSURE

3 in (7.8 cm) per year

The Peru–Chile Trench (also called the Atacama Trench) is the longest ocean trench, marking the point at which the Nazca Plate meets the South American Plate. The Nazca Plate is primarily dense ocean crust and so is being subducted beneath the more buoyant South American continental plate. The South American crust has been deformed and thickened A

B

Volcanic island

AREA

63 square miles (164 square km)

Easter Island lies near the East Pacific Rise, which separates the Pacific Plate to the west from the Nazca Plate to the east. The island is the highest point of the Easter Fracture Zone, a series of ridges and trenches marking a transform fault running 3,650 miles (5,900 km) across the floor of the South Pacific, from the Peru–Chile Trench in the east to the Tuamotu Archipelago (see p.477) in the west. Easter Island was named in 1722 by Dutch sailors, who came across it on Easter Sunday. It had been settled at least 1,000 years earlier by Polynesians, who today call the island Rapa Nui. The island is famous for its giant stone statues, which are known as moai, found in groups along the coast. About half of the 900 statues remain unfinished in the quarry—it seems statue-carving stopped abruptly

C

150˚W

1

D

140˚W

Sca rp

Bauer

10˚S

130˚W

e 120˚W dg Ri ge o d d ra Ri o va Al nt e i rm Sa

Bauer Basin

Chiclayo

BRAZIL

Trujillo

c Rise

PERU

Galapago s Rise

Bau

1,027m (3,370ft)

er F ract ure Z

ract u

one

Mendañ

a F

Zo re u t rac

ne

Basin 5,338m (17,514ft)

P Ri dg e

a Na zc 1,300m (4,265ft)

30˚S

3

La Serena 30˚S

1,914m (6,368ft)

SCALE 0

4 400

200

0

200

600

400

800

600

140˚W

B

Valparaíso

1000 miles

800

150˚W

A

Islas Juan Fernández

1,000 km

130˚W

C

120˚W

D

E

110˚W

F

AT L A S O F T H E O C E A N S

Ferris Seamount

h

Chile Basin

Islas de los Desventurados

20˚S

8,069m (26,474ft) Tropic of Capricorn

Tr e n c

ne ure Zo

Arica

hile

4,076m (13,373ft)

OCEAN Roggeveen Basin

ru –C

ise

Easter Island

2

188m (619ft)

Sala y Gomez Ridge t r Frac Easte

e

5,338m (17,514ft)

333m (1,093ft)

PAC I F I C Sala y Gomez

10˚S

Peru

re Z one

1,481m (4,859ft)

3

476m (1,562ft)

1

Lima

R oza

Yupanqui Basin

Tropic of Capricorn

4

110˚W

d Men

20˚S

F

5,852m (19,200ft)

Dan aF

East P acifi

2

Easter Island’s enigmatic moai statues were carved from soft volcanic rock taken from Ranu Raraku, one of the island’s many volcanic craters. E

4,175m (13,698ft)

1

MOAI

CHILE

LENGTH

TYPE

NUMBER OF ISLANDS

by the convergence, creating the Andes Mountains. Melting of the rocks around the subducting slab has led to volcanism and many of the Andes’ tallest peaks are volcanoes. Earthquakes along the trench produced nine large tsunamis during the 20th century, resulting in more than 2,000 deaths. The trade winds drive surface waters offshore throughout most years, leading to upwelling of nutrient-rich deep water off the coast of Peru. This upwelling makes the water very productive and yields large fish catches, predominantly anchovies and sardines. Under El Niño (see pp.68–69) conditions, however, the wind direction reverses and the fish catch plummets.

PACIFIC OCEAN F2

about a century before the first European explorers arrived. It is thought that the island’s forests and soil became so depleted that the islanders’ society collapsed in a violent struggle over access to rapidly diminishing resources.

PACIFIC OCEAN B3

IN THE EASTERN SOUTH PACIFIC,

479

480

A

THE PACIFIC OCEAN

Southeast Australia and New Zealand

B

150˚E PACIFIC OCEAN B6

Coral Sea Islands

LENGTH

400km (250 miles)

MINIMUM WIDTH

1

Coral Sea

100km (62 miles)

TO THE NORTHEAST OF AUSTRALIA, ocean

Kermadec–Tonga Trench LENGTH DEPTH

2,500km (1,550 miles) 10,800m (35,430ft)

RATE OF CLOSURE

15–24cm (6–9in) per year

The Kermadec–Tonga Trench runs between the North Island of New Zealand and the island of Tonga. The Pacific Plate converges with the Australian Plate in this suduction zone. At its northern end, closure rates of 24cm (9in) per year have been measured – the fastest recorded plate

motion yet. The older oceanic crust of the Pacific Plate is sinking below the more buoyant crust of the young oceanic Australian Plate. The Tonga Ridge and the older Lau Ridge formed as arcs of volcanoes. The rapid motion has caused extension of the Australian Plate and the opening of a back-arc basin between the two ridges, in the Lau Basin. The latest addition to this island chain is new land at the southern end of Hunga Ha’apai that emerged in 2009 after several undersea volcanic eruptions. Together with Fiji and Samoa, the 36 islands of Tonga are the cradle of the Polynesian seafaring culture, which had stretched across the South Pacific by the 12th century.

20˚S

Mackay

e Re

PACIFIC OCEAN G4

The Bass Strait separates Tasmania from Australia, overlying a shallow shelf around 50m (160ft) deep. Strong winds and currents from the Southern Ocean combine with the shallow depth to make its waters notoriously rough. Hundreds of ships were wrecked on its shores during the 19th century, before the erection of lighthouses made navigation safer. Natural gas fields were discovered beneath the eastern Bass Strait in the 1960s and 1990s.

Gre at er rri Ba

currents flow from the east, feeding the warm East Australia Current, which sweeps south along the Australian coast, before turning east to flow north of New Zealand. South of New Zealand, the Antarctic Circumpolar Current flows from west to east. New Zealand straddles a major tectonic boundary between the Pacific and Australian plates.

Mellish Rise

Bass Strait

f

2 Tropic

n

pricor

of Ca

Fraser Island

Brisbane Gold Coast

30˚S

AUSTRALIA

PHILLIP ISLAND

Newcastle 4

Tasman Sea AREA

2.3 million square km (890,000 square miles)

MAXIMUM DEPTH INFLOWS

LORD HOWE ISLAND

The warm waters of the East Australia Current allow Lord Howe Island to host the world’s most southerly coral reef.

5,945m (19,500ft)

Southern Ocean, Coral Sea

This warm sea was discovered by Dutch explorer Abel Tasman in 1642, while looking for Terra Australis (the Southern Land). On this voyage he become the first European to reach the islands of Tasmania, New Zealand, Tonga, and Fiji. The area was not visited again until James Cook’s voyage in 1768. On a later voyage, in 1644, Tasman succeeded in finding the continent of Australia. The Tasman Sea has a subtropical climate in the north, but the influence of cold sub-Antarctic water makes it temperate in the south.

Sydney

PACIFIC OCEAN H3

Southwest Pacific Basin AREA

Tasman Plain

PACIFIC OCEAN C5

Wollongong

23 million square km (8.9 million square miles)

MAXIMUM DEPTH INFLOWS

5,655m (18,500ft)

Pacific Ocean, Southern Ocean

5

The Southwest Pacific Basin lies east of New Zealand and the Kermadec– Tonga Trench. It is bounded in the east by the East Pacific Rise (see p.478), in the south by the Pacific–Antarctic Rise, and in the north by the Polynesian island chains. The Louisville Ridge is the only significant chain of seamounts and much of the basin floor is an abyssal plain. There are extensive deposits of manganese in the northern and southern parts of the basin.

Melbourne

Cape Everard 2,620m (8,596ft)

South East Point Cape Otway Bass Strait

Furneaux Group

King

40˚S Island

Tasmania

6

Hobart East Tasman Plateau

3,460m (11,352t) PACIFIC OCEAN E5

TYPE

Micro-continental island group

AREA

268,680 square km (103,700 square miles)

NUMBER OF ISLANDS

2 main islands

(700 smaller islands)

Tasman Plateau

140˚E

7

c Fra an

50˚S

e tur Zo

CAMPBELL ISLAND

ne

New Zealand separated from Australia and Antarctica 80 million years ago, and is now positioned at the boundary between the Pacific and Australian plates. The largely transverse Alpine Fault runs 700km (435 miles) across the South Island. Crustal compression and distortion across a 250km(155-mile-) wide zone has raised the Southern Alps over 4,000m (13,000ft) above sea level. The plate boundary continues north as the Hikurangi Trench, a classic subduction zone

730m (2,395ft)

m Tas

AT L A S O F T H E O C E A N S

New Zealand

producing volcanism on North Island, and south as the Macquarie Ridge, where shallow subduction has uplifted the Australian Plate. A swarm of earthquakes hit the South Island between 2010 and 2012, the largest of which killed 185 people and destroyed the historic cathedral in Christchurch in 2011. The main islands of New Zealand are the highest points of an extensive area of continental crust that includes the Campbell Plateau, Challenger Plateau, and Chatham Rise. To the southeast, Campbell Plateau is the world’s largest area of submerged continental crust.

The southernmost of New Zealand’s subantarctic islands, Campbell Island is primarily volcanic in origin.

140˚E

A

B

l New Ca

South Fiji Basin

prico

rn

Hauraki Gulf

Bay of Plenty

ch

Tre n

gi T re nc h

llon a Va lley

Be

Wellington

30˚S

5,655m (18,551ft)

5

ge Rid

Napier Hawke Bay it Cook Stra

Challenger Cape Plateau Farewell

East Cape

North Island

Cape Egmont

5,512m (18,085ft)

(390ft)

NEW ZEALAND

3

4

Raukumara 119m Plain

Auckland

Gascoyne Seamount

Pacific

ville Louis

Ri dg e

Northland Plateau

Ke r

f

Cape Reinga

Southwest

PA C I F I C OCEAN

Hik ura n

se

idg e m Ha ad ec v Ri re T dg ro ug e h

Ri dg e

10,047m (32,964ft)

Co l vi lle R

ga

or tN

Ri

s We

we

Re

Ho

in

ol k

Tasman Sea

of Ca

2

Basin

de c

sin

Gazelle Basin

Taupo Tablemount

Tropic

Kermadec Islands

Ke rm a

ia Ba

1,039m (3,409ft)

398m (1,306ft)

Lord

Barcoo Tablemount

170˚W

10,800m (35,435ft)

e

edon

Norfolk Island

Lord Howe Island Ball’s Pyramid

20˚S

10,567m (34,736ft)

Ozbourn Seamount

Thr ee K ings Rise

ounts

3,319m (10,890ft)

Tongatapu Group

Ton ga Rid ge

10m (33ft)

Derwent Hunter Guyot

Ba

Hebrides

TONGA sin

Rid ch Tr e n

Lau

ew

dg Norfolk Ri

m we Sea Lord Ho

N

ge

ge

Nouméa

1

Vava’u Group

4m (13ft)

d Ri

o Tr

NEW ug h CALEDONIA

ds an

a ni do

Isl

Koro Sea

FIJI

North Fiji B asin

Pentecost

180˚

481

roup

le Ca

Loy alty

Erromango

H Lau G

ew Bellona Plateau

VANUATU

s de bri He

N

G

Viti Levu Suva

170˚E

New

160˚E

F

Tr en ch

E

To ng a

D

Lau

C

33m

nd

h ug

Fio rdl a

Tho ms on Tr o

5,369m (17,616ft)

Foveau x 216m (709ft)

Christchurch (108ft) Banks Peninsula Canterbury Bight

South Island

Dunedin

6 Chatham Islands

KEY sea level

Bounty Troug h

250m (800ft)

Stra it Stewart Island

500m (1,600ft)

4,298m (14,102ft)

2,000m (6,500ft)

7

3,000m (9,800ft)

Antipodes Islands

5,000m (16,400ft)

Bollons Tablemount

ie R idg

e

Campbell Plateau

1,000m (3,300ft)

Bounty Islands

land

50˚S

Ma cqu ar

Campbell Island

Macquarie Island 150˚E

C

100

0

160˚E

170˚E

D

sea depth

SCALE 0

E

200

100

180˚

300

200

400

maximum depth on map

500km

300

400

170˚W

F

seamount

500 miles

tectonic plate boundary

160˚W

G

H

8

AT L A S O F T H E O C E A N S

Snares Islands 60m (197ft)

Auckland Islands

40˚S

Chath am R is e

A

THE SOUTHERN OCEAN

Transkei Basin

˚S

5,819m (19,092ft)

dia

c–

5,115m (16,782ft)

3

nt

i

Se D amavi ous nts

tri As

Discovery Seamounts

ge id R A

c

Isla sO

Ocean Floor 6

e

South S a

e

1,748m (5,735ft)

rca da sR

id g

e Zon

5

Lazarev Sea

idge

r Fractu

d-

ti

nd

Cape Norvegia

5,012m (16,444ft)

Tr wich ench

7,152m (23,466ft)

187m (604ft)

ti Sco

3,667m (12,031ft)

aS ea

d an

d an lkl Fa

lk l Fa

la pio Za idge R

ent pm

u ea at Pl

car Es

Argentine Basin

Weddell Plain

East Scotia Basin

South Georgia

30˚W

Ri dg e

Maud Rise

South Sandwich Fracture Zone

Gough

Mi

n tla

South Orkney Islands Bra

nsfi

Basin

Cape Horn

˚S

30 SCALE

0

200

400

200

Fresh glacial water refreezes on contact with cold ocean water, which is kept liquid by its salt.

600

400

800 1,000 km

600

800

1,000 miles

SOUTH AMERICA

60˚W

A

B

eld S

trait South Shetland Islands Dr ak eP ass ag Yaghan e

Falkland Islands

0

N

d

4

America–Antarctica R

ATLANTIC OCEAN

Tabular icebergs and sea ice can be found drifting in much of the Southern Ocean throughout the year.

AT L A S O F T H E O C E A N S

a tl

SO UT HE R

A

SEA-ICE AND ICEBERGS

The Southern Ocean is unusual in not having a well-defined basin bounded by land masses: it surrounds the South Pole and extends for 360˚ of longitude. There are a series of deep basins lying between the continental shelf and the ridges at the edge of the Antarctic Plate. The continental shelf is narrow, and deeper than that of other continents due to the depression of the crust under the weight of the 11/2 -mile- (2.5-km-) thick Antarctic Ice Sheet. The surrounding spreading ridges drove the break up of the supercontinent of Gondwana, starting when Africa began to move north 165 million years ago. An area of thick ocean crust, the Kerguelen Plateau, lies between the Southern and Indian oceans. This is one of the largest submarine plateaus, and it is composed of flood basalts that erupted about 97 million years ago.

Atlantic– Indian Basin

In

Cape Basin

0˚

The eastward-flowing Antarctic Circumpolar Current is the strongest in the world. It flows up to 9,800 ft (3,000 m) deep and carries 4.8 million cubic ft (135,000 cubic meters) of water per second through Drake Passage. It diverts heat flowing from the equator, isolating Antarctica and causing the buildup of the thick Antarctic ice cap. Cold currents branch off up the eastern sides of the Indian, Atlantic, Pacific oceans. The Circumpolar Current (also known as the West Wind Drift) is driven by the prevailing westerly winds, which blow uninterrupted by any landmass. Wind speeds in the Southern Ocean are the highest in the world: the “roaring forties” give way to the “furious fifties” and the “screaming sixties” as one sails south.

Lena Seamount

e Zon

n Ridge

30

Cape of Good Hope

Prince Edward Islands

re ctu Fra

Cape Town

2

Ocean Circulation

FROZEN WATERFALLS

ar d Edw

Africana Seamount Agulhas Plateau

Crozet Islands

o an l C ise e R D

ce Prin

WEDELL SEAL DIVING BENEATH THE ICE

Crozet Plateau

Port Elizabeth

THE SOUTHERN OCEAN COMPLETELY

surrounds Antarctica and links the Indian, Atlantic, and Pacific oceans. Antarctica’s coast was not sighted until 1820, and its shores were not fully explored until the 20th century. The Southern Ocean is generally described as being south of 60° latitude, but is physically better defined by the extent of the Antarctic Circumpolar Current.

30˚E

AFRICA

1

C

ue biq am ent Moz arpm Esc

The Southern Ocean

B

30 ˚S

482

C

D

E

G

West Australia Current

Benguela Current

90˚E

Kerguelen

Ke rg

INDIAN OCEAN

Heard and McDonald Islands

ue

Weddell Gyre

n le

EAN

Cape Batterbee

of w inte r

pac k

t

In

di

Cu r ren

t

Falklands Current

an

ice

R

unts

id

Peru or Humboldt Current

ge

ctic Antar

SURFACE CURRENTS

limit of summer pac k ice Davis Sea Vincennes Bay Cape Poinsett

s

South Indian Basin

rli

ast r E erli

es

Pol a

LützowHolm Bay

We ste

u rc Ci

es

Cape Antarctic C ircle Darnley Mackenzie Bay

erl ie

OC

limi t

as

We st

Enderby Plain

Ross Sea Gyre

ut

he

60˚S Ba nza re S eamo

4,684m (15,368ft)

So

u ea at Pl

4,285m (14,059ft)

184m (604ft) 5,386m (17,671ft)

483

m po lar

60˚E

F

We ste r

l ie s

Dumont D’Urville Sea

E 150˚

SURFACE WIND Beaufort Scale 0–3 3–5.5 over 5.5

ANTARCTICA

Speed 0–10 mph (0–16 km/h) 10–25 mph (16–40 km/h) over 25 mph (over 40 km/h)

95m (312ft)

Balleny Islands

South Pole Cape Adare

ter pac limit of win

k ice

dg

Ri

U O S

90˚W

D

Ri s e

800 ft (250 m)

E H T

1,600 ft (500 m) 3,300 ft (1,000 m) 6,500 ft (2,000 m)

ne

PACIFIC OCEAN

Eltanin Fracture Zone

rd Frac tu E

re Z o n e

Southwest Pacific Basin

9,800 ft (3,000 m) 16,400 ft (5,000 m)

seamount

8 sea depth maximum depth on map

150˚W

120˚W

F

7

land

E as t P a Rise cific

M e na

Chat ham

sea level

60˚S

Mornington Abyssal Plain

6

KEY

re Zo Fractu Udintsev

Southeast Pacific Basin

6,034m (19,798ft)

180˚

30 ˚S

B el ling sh Plain ausen

EA N

tic rc

Antarctic Circle

OC

c–A

nta of limit

A

ice

Bollons Tablemount

N

Thurston Island

ac k er p m sum

North Island

G

H

I

AT L A S O F T H E O C E A N S

4,094m (13,432ft)

Amundsen Sea

5,415m (17,767ft)

5

Wellington

New Zealand

R

Alexander Island Bellingshausen Sea

Pacifi

4,283m (14,058ft)

Ellsworth Land

nP lain

ic Peninsula

un ds e

rct

m

An ta

Weddell Sea

Campbell Dunedin Plateau

and Isl

Roosevelt Island

Ronne Ice Shelf

Challenger Plateau

th ou

Ross Sea Berkner Island

S

e

Ross Ice Shelf

THE SOUTHERN OCEAN SOUTHERN OCEAN C3 AND D4

Filchner–Ronne Ice Shelf

north from Antarctica toward South America, separating the Weddell Sea from the Bellingshausen Sea. At its northern end, a chain of islands marks the edge of the Antarctic Plate.

16,440 ft (5,012 m)

Southern Ocean, Filchner-Ronne Ice Shelf, Larsen Ice Shelf INFLOWS

YOUNG WEDDELL SEAL

ice west, then north up the Antarctic Peninsula, before turning east with the Circumpolar Current. The Antarctic continental shelf is at its widest here, with shallow banks extending out from under the Filchner–Ronne Ice Shelf.

B

A

C 60˚W

70˚W

Hero

nd etla Sh h h g ut u So Tro

5,204m (17,074ft)

The Bellingshausen Sea is named after Fabian von Bellingshausen, an officer in the Imperial Russian Navy, who was the first to sight the coast of Antarctica, in 1820. It is one of several parts of the Southern Ocean that is rich in krill, the basis of a productive marine food chain.

ROTHERA RESEARCH STATION.

D

Elephant Island

E 40˚W

50˚W

South Orkney Orkney Islands Deep

e Powell eZ dg 187m one Basin Ri trait S e d (614ft) South Shetland nc fiel Joinville Island ra Islands ans du Br n Dundee Island Esperanza James Ross Island Base Brabant Island Marambio Base Snowhill Island Anvers Island Palmer Base Robertson Island Jason Peninsula Renaud Island Faraday yo n Biscoe Islands Base an Ca nd C Churchill Peninsula Yelcho n Lavoisier Island i etla t h r S a Larsen th Ice Shelf ou Adelaide Island S n o Cape Agassiz ny Rothera Base Ca ce Martín n a Marguerite San r Base Endu Hearst Island Bay

uc Br

e

F

30˚W South 210m e (689ft) g Sandwich d i R

Islands

Gra ham

n

C oa s

W 10 ˚

d

An t

f su

mm er pa c

Co ast

Berkner Bank

Korff Ice Rise

Georg von Neumayer Base

ld itpo LuCoast Belgrano II Base

Berkner Island Filchner

Dr

ANTARCTICA

Sanae Base Fimbul Ice Shelf

on ni La n

Co ast

C

10 ˚

˚W 20

D

W

0

30˚W

40˚W

˚S

50˚W

B

60˚W

˚W

100

200

300

400

3 0˚

4

500 km

˚S

˚W

10 0

80

ree n

ANTARCTICA

0

80 70˚W

W a lg

SCALE

Henry Ice Rise

80

110 ˚W

Ci rc le

d

Canisteo Peninsula

tic

˚S

Ellsworth Land

Behaim Seamount

k ice

Cape Norvegia Riiser–Larsen Ice Shelf Kronprinsess Martha Kyste

Brunt Ice Shelf Halley Base

ar c

70

oa st

n

Ca ny o

y

ar tic C

gu a

An t

En

gli sh

Ur u

e

an yo n

Sa n

M

Loubet Coast

lim it o fw

An t

n la ch ts

on ny Ca

lim it o

au M nd

˚S

4,800m (15,749ft)

Lyddan Island

Ronne Ice Shelf

2

g

70

eu D

Cape Fiske

ille Orv

˚W

AT L A S O F T H E O C E A N S

Bryan Coast

90

A

Ronne Basin

443m (1,453ft) Belgrano Bank

5,012m (16,444ft)

Weddell Plain

Ice Shelf

Amundsen Sea

Bear Peninsula Martin Peninsula

nsula

10 ˚W

Weddell Sea

Dollerman Island Steele Island Cape Knowles

Lassiter Coast

4

King Peninsula Burke Island 1

Peni

und

Farewell Island Dustin Island Thurston Island C hts E ig ˚W

st Coa

I So

Rydberg Peninsula 10 0

t

Spaatz Island

Smyley Island

3

ctic

eV

Bellingshausen Sea

Alexander Island

Black

org

˚W

90

Charcot Island le 4,094m c rc (13,432ft) i ki C pac Latady Island r it c e m c ar f sum Peter I it o m i Island l

tar

Ge

Rothschild Island

1

SOUTHERN OCEAN

An

int e

rp ac k

ic e

2

S th

u So 1,780m So uth (5,840ft) San Li g dw e ti ich Rid Fra ge ctu re Z 60˚ on S e

yo n

Bellingshausen Plain

˚S

60

5,404m (17,731ft)

7,152m (23,466ft)

E

5,259m (17,255ft)

3,000 ft (900 m)

13,400 ft (4,094 m)

Southern Ocean, George VI Ice Shelf

La nd

˚W

80

1

Scotia Sea Frac tur

INFLOWS

The Filchner Ice Shelf was first sighted by the German explorer Wilhelm Filchner in 1912. It lies to the east of Berkner Island. To the west of Berkner Island lies the Ronne Ice Shelf. It was charted from the air by American naval commander Finn Ronne in 1947. Together these two shelves make up the second-largest floating ice shelf by area, and the largest by volume. The bedrock of the ice-covered Berkner Island in fact lies below sea level. Although fed by glaciers from the continental ice cap, and grounded on its landward side, most of the area of the Filchner–Ronne Ice Shelf is floating in the Weddell Sea. The ice shelf itself is up to 3,000 ft (900 m) thick, and the underlying seafloor is up to 4,600 ft (1,400 m) deep.

1.1 million square miles (2.8 million square km)

232,000 square miles (600,000 square km)

MAXIMUM DEPTH

Arctic Ice Sheet

INFLOWS

Weddell Sea

The Weddell Sea is named after British seal hunter James Weddell, who reached a latitude of 74°34’ South in 1832, the most southerly point that would be reached for the next 80 years. It is mostly covered with pack ice, even in summer, and is the source for 70 percent of the cold Antarctic bottom water. A clockwise gyre carries

AREA

166,000 square miles (430,000 square km)

MAXIMUM THICKNESS

SOUTHERN OCEAN D2

MAXIMUM DEPTH

Bellingshausen Sea

˚W

AREA

THE ANTARCTIC PENINSULA EXTENDS

AREA

SOUTHERN OCEAN A1

20

The Antarctic Peninsula

an dw ichT rench

484

100

0˚

E

200

300

500 miles

400

˚E 10

F

B

˚S

70

˚W

Bank lin

14 0

Ise

˚S

3,774m (12,382ft)

Ross Bank

st Coa

Whales FurrowBay s

THE ROSS SEA IS A LARGE BAY

situated between Marie Byrd Land and Victoria Land. Water circulates in a clockwise gyre, with a westward coastal current being turned north along the coast of Victoria Land to join the eastward Circumpolar Current.

Ross Sea 370,000 square miles (960,000 square km)

MAXIMUM DEPTH INFLOWS

8,300 ft (2,500 m)

Southern Ocean, Ross Ice Shelf

The Ross Sea is named after the British naval officer James Clark Ross, who charted this part of the Antarctic coast in 1841. The volcanoes Mount Erebus and Mount Terror on Ross Island are named after the two ships under his command during this expedition. Ross Island is home to the largest scientific base on ICEBREAKER AT SEA

A Russian icebreaker is shown here among drifting ice in the Ross Sea, with the Transantarctic Mountains in the background.

Marie Byrd Land

is

0 12

Antarctica, the American research station at McMurdo Sound. The Ross Sea can be largely ice-free during the summer months, making for an easier approach to the South Pole than is possible via the Weddell Sea.

˚W

80

˚S

˚W 150

0

100

200

100

D

Ross Ice Shelf 188,000 square miles (487,000 square km)

MAXIMUM THICKNESS INFLOWS

200

400

4

500 km

300

E

SOUTHERN OCEAN C3

AREA

300

400

500 miles

2,600 ft (800 m)

Antarctic Ice Shelf

The southern half of the Ross Sea is overlain by the world’s largest floating ice shelf, the Ross Ice Shelf, which extends up to 280 miles (450 km) from the shore of Antarctica. The Norwegian explorer Roald Amundsen started his successful expedition to the South Pole in 1911 by crossing this ice shelf. It ranges in thickness from about 820 ft (250 m) at the ice front to 2,600 ft (800 m) inland. Ice floats with most of its volume underwater, making the height of the ice front above sea level about 65–100 ft (20–30 m). The shelf flows seaward at about 3,000 ft (900 m) per year, propelled by the accumulating weight of compacted snow that falls on the high plateau of the Antarctic Ice Sheet. Accumulation on the ice cap is thought to be balanced by iceberg calving at the front of Antarctica’s ice shelves and melting on their underside.

F

DISCOVERY

ICE SHELF SEAS Ice-core drilling, seismic sounding, and ice-penetrating radar have all been used to measure the thickness of floating ice shelves from the surface. Now, autonomous underwater vehicles (AUVs) are being deployed to explore the “cave seas” beneath the ice. They are able to gather more detailed information about sea floor depth, ice thickness, ocean temperature, pressure, and salinity.

SEA FLOOR BENEATH THE ICE

AT L A S O F T H E O C E A N S

AREA

160˚ W

S 80˚

The Ross Sea SOUTHERN OCEAN D2

170˚W

C

0

uld

Coast

180˚ 170˚E

˚E

˚E 160

0 15

˚E

B

0 14

A

˚E

3

SCALE

Go

oast

tectonic plate boundary

13 0

t s

˚W

E

E

Dean Island

14 0

Dufe kC

120 ˚

120 ˚

Base

e Saunodas C

C le S ip

sea depth

110˚E

Cape

ANTARCTICA

seamount

maximum depth on map

Hobbs

Bank Rupp BurksGrant Coastert Island Russkaya

t ku t Ba oas C

Ross Ice Shelf

on l et ack st Sh Coa

˚E

Newman Island

Sulzberger Bay

b ob H oas C

ar y Hilloast C

13 0 land

4

Prestrud Bank

II oast rd V la se C wa su EdPenin Shira

Little America Basin

Roosevelt Island

16,400 ft (5,000 m)

2

4,285m (14,058ft)

Ross Sea

Scott Base White Island

ANTARCTICA

3,300 ft (1,000 m) 6,500 ft (2,000 m) 9,800 ft (3,000 m)

3

70 Pennell Bank

Ross Island

McMurdo Base

1,600 ft (500 m)

Amundsen Plain

Coulman Island

Franklin Island Beaufort Island

Scott

sea level 800 ft (250 m)

Manson Bank

Crary Bank

KEY

limit of sum mer p ack ic e

oa st

˚E

d Lan

14 0

1 irc le

13 0˚ W

a Victori

2

Cape (3,907ft) Adare

Iselin Seamount

n

V

1,191m

Cape Oates Ban k Leningradskaya Cheetham Base t as Co

Bo rch Co grevin ast k

e org

150˚W

SOUTHERN OCEAN

sB a si

it o

im

Ge

160˚W

485

An t ar cti cC

Adare Seamounts

Cape Hudson

Cape Freshfield

F

Scott Seamounts

oun ts

Virik Bank

cle Cir

tic rc ta

ds

170˚W

E

Scott Island

yon Can ott Sc

An

Bal leny Isla n 95m (312ft)

f su

˚E

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ICE-SHELF REMNANT

Although most of the Larsen B ice shelf broke up in 2002, a part of it, visible on the left, remains. This contains deep crevasses, making it prone to further disintegration.

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Ice-shelf Breakup ICE SHELVES IN RETREAT

Ice shelves are extensions of Antarctica’s ice sheets

MELTWATER POOL In the summer, meltwater collects in low-lying parts of the surface of an ice shelf, including crevasses and depressions. Melting also occurs on the underside.

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DISAPPEARING ICE SHELF

Larsen Ice Shelf Collapse The Larsen Ice Shelf occupies the eastern shore of the Antarctic Peninsula. In 1995, the northern part of the ice shelf, Larsen A, broke into tiny fragments during a storm. In 2002, most of the central part, Larsen B, disintegrated in a similar manner over a few weeks. At the moment, the largest Weddell Sea part of the shelf, Larsen C to the south, seems to be Ronne Larsen stable, although it Ice Shelf Ice Shelf Tr East Antarctica ans too lost a large a nt West ar area in 1986. Antarctica

Area of Larsen A collapse in 1995 Area of Larsen B retreat between 1995 and 2002

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GIANT ICEBERGS

Area of Larsen B collapse in 2002

AT L A S O F T H E O C E A N S

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Extent of Larsen ice shelf up to 1995

Present day extent of ice shelf

LARSEN B COLLAPSE Extensive meltwater pools are visible in a satellite image of the Larsen B Ice Shelf taken on January 31, 2002, before it broke up (top). The collapse itself, on March 7, 2002, is shown in the lower image. The ice shelf broke into a multitude of small fragments, and a few larger ones, which quickly dispersed into the Weddell Sea. It is possible that meltwater helped push surface crevasses through the entire 720 ft (220 m) thickness of the Larsen B Ice Shelf.

ICEBERG B-15 One of the largest icebergs ever seen, at 185 miles (300 km) long, 25 miles (40 km) wide, and 200 ft (60 m) high, B-15 broke off from the Ross Ice Shelf in March 2000. It drifted around the Ross Sea for several years, disrupting navigation and penguin migration. The iceberg eventually broke into smaller pieces, some of which were seen not far from New Zealand in November 2006.

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Area of further retreat between 2002 and 2012

CRACK IN LARSEN A The additional weight of meltwater may increase the pressure at the base of a crevasse, causing it to penetrate deeper into the ice shelf and to widen.

CRACKING UP

over the sea. Continually pushed away from the land by the weight of accumulating snow, an ice shelf gradually advances over the ocean until its front breaks off to form a tabular iceberg. This advance and retreat is part of a natural cycle, but in the Antarctic Peninsula, some small ice shelves have suffered catastrophic collapses as a result of regional warming of 5˚F (2.8˚C) over the last 50 years. In 2008, for example, the Wilkins Ice Shelf lost around 200 square miles (500 square km). Although the loss of floating ice does not affect global sea levels, it seems that the adjacent continental ice sheet may become unstable if it loses the “buffer zone” provided by an ice shelf. After the Larsen B Ice Shelf collapsed in 2002, scientists measured nearby glaciers flowing between two and eight times faster than they had before. It is not yet clear whether the larger Ronne and Ross ice shelves act as a similar brake on the West Antarctic Ice Sheet. If the regional warming continues and the West Antarctic Ice Sheet collapses as a result, global sea levels could rise more than 16 ft (5 m), threatening densely populated coastal areas worldwide.

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GLOSSARY

Glossary A abyssal Relating to oceanic depths greater than about 6,500 ft (2,000 m). The abyssal plain is the flattish plain at 13,000–20,000 ft (4,000–6,000 m) that forms the bed of most ocean basins. The abyssal zone is the region of both seabed and open water between 6,500 ft (2,000 m) and the abyssal plain. See also bathyal, hadal. air mass A body of air with relatively uniform temperature and pressure, forming above a given region of Earth’s surface. Its characteristics derive from this surface region and are distinct from surrounding air masses. “Tropical maritime” and “polar continental” are examples. albedo The extent to which incoming radiation is reflected from a surface. Ice has a high albedo, reflecting most of the Sun’s radiation reaching it. algae Simple plants and plantlike protists that can photosynthesize, ranging from seaweeds (macroalgae) to microscopic plankton (microalgae). Some types of algae, such as green microalgae and green seaweeds, are often classified as plants. Red and brown seaweeds are also algae, but are often classified separately. Singular alga. See also cyanobacteria, photosynthesis, protists, seaweed. amphipods A group of small, common, shrimplike crustaceans, flattened from side to side, which live mainly on the sea floor and feed on detritus (dead material). anadromous Of fish: living most of their lives at sea but entering rivers to breed, for example, the salmon. See also catadromous. anaerobic Relating to processes occurring without oxygen, or to organisms that are able to live in the absence of oxygen. See also anoxic. anemones Solitary cnidarians that live attached to surfaces and grab passing prey with their stinging tentacles. See also cnidarians, coral, polyp. annelids see segmented worms. anoxic Of a habitat: without available oxygen for living creatures. Antarctic Circle Line of latitude in the Southern Hemisphere south of which there is at least one day of 24-hour sunshine and at least one day of 24-hour darkness per year. anticyclone A pattern of circulating air in the atmosphere with high pressure in the center; usually associated with settled weather. See also cyclone. archaea A group of tiny, single-celled organisms. Like bacteria, they have no cell nucleus, but are classified

separately. They often live in extreme environments, such as deep-sea vents. See also bacteria. Arctic Circle Line of latitude in the Northern Hemisphere north of which there is at least one day of 24-hour sunshine and at least one day of 24-hour darkness per year. arthropods A major group (phylum) of invertebrate animals with jointed legs and a hard outer skeleton. It includes crustaceans (crabs, shrimp, and relatives), insects, spiders. See also crustaceans, exoskeleton. asexual reproduction Reproduction that does not involve combining the genes from two individuals (sex). It can consist of splitting or fragmenting the body, the budding of new individuals, or specialized structures forming, such as spores. atoll A low, ring-shaped island, or series of arc-shaped islands, forming the rim of a shallow lagoon. The structure results from an accumulation of coral on top of a sunken volcano. See also lagoon. authigenic Of sediments: formed locally in the ocean (especially via chemical processes), not transported from elsewhere. See also sediment. autotroph An organism, such as a plant, that can make its own food, rather than eating or absorbing food produced by other organisms. See also photosynthesis, primary producer.

B backshore Part of the shore above the average high-water mark, affected by the sea only during the highest tides and storms. See also foreshore. backwash The flow of water back to the sea after a wave has broken on a beach. bacteria Microscopic single-celled organisms abundant in all ecosystems. Their cells are much smaller than those of animals and plants and have no nucleus. See also archaea, cyanobacteria, protists. baleen Horny plates in the mouths of some whales that are used to strain food, such as krill, from the water. bank A shallow region of sea surrounded by deeper water. Often the site of productive fisheries. bar A long, narrow, offshore deposit of sediment lying parallel to a coastline. Bars may be permanently submerged, or exposed at low tide. A bar that is always exposed is a barrier island. A bar across the mouth of a bay and attached to the coast is a baymouth bar. See also barrier island, spit.

barbel Sensitive fleshy projections often found in pairs around the mouths of some fish. barnacles Specialized crustaceans whose adults live attached to rocks and other surfaces. They are protected by hard shell-like plates and filterfeed using highly modified limbs. See also crustaceans, filter feeding. barrage Human construction built across an estuary or inlet to protect against flooding by heavy seas. barrier island A permanently exposed bar of sand or pebbles lying parallel to a coastline. A barrier beach is a similar structure, but can be attached to the mainland at one or both ends. barrier reef A coral reef parallel to, but some distance from, a shoreline. basalt A common volcanic rock; originally solidified lava. The rock of the ocean floor is mainly basalt that has spread from mid-ocean ridges. basin see ocean basin. bathyal Relating to ocean depths between about 660 and 6,500 ft (200 and 2,000 m). The bathyal zone is the region of seabed and water column between these depths. See also abyssal. beach face The steeply sloping part of a beach, below a berm. See also berm. benthos Living organisms that live on or in the seabed (benthic organisms). berm A ridge of sediment high on a beach, left behind by a high tide. Also called a beach ridge. biodiversity The diversity or variety of living organisms; determined by, for instance, the number of species, or the variation within species. biogenic Formed by the action of living organisms. bioluminescence The production of light by living organisms. biomass The total mass or weight of living organisms in a given area. biome Any large-scale association of plants and animals, especially one dependent on particular climatic conditions. Mangrove swamp and the abyssal plain are marine biomes. bioturbation Disturbance and mixing of seafloor sediments, usually by burrowing animals. bivalves Mollusks, such as clams, mussels, and oysters, that have a shell made up of two hinged halves. Most bivalves move slowly or not at all, and are filter feeders. See also filter feeding, mollusks. black smoker A hydrothermal vent in which the emerging hot water is colored black with dark minerals. bloom A rapid growth of plankton, often turning the water cloudy and

greenish; usually a response to an increase in the availability of nutrients in the water. See also phytoplankton. blue-green algae see cyanobacteria. bony fishes The large group that includes all fish species except jawless fishes, sharks, and other cartilaginous fishes. See also cartilaginous fishes. bore see tidal bore. brackish Saltier than fresh water, but less salty than typical ocean water. breaker zone The zone of a beach, or other shoreline, where waves break. breakwater An artificial barrier built in the sea, usually near a harbor, to protect against waves and heavy seas. brittlestars Echinoderms with narrow, jointed, flexible arms; related to starfish. See also see echinoderms, starfish bryozoans Filter-feeding colonial animals that live attached to surfaces, such as seaweed fronds, either as flat sheets or as tufty, plantlike growths. Sometimes called “moss animals.” bycatch In fishing, the portion of a catch made up of non-target species.

C calcareous Consisting of or containing calcium carbonate. calcium carbonate The chemical CaCO3. It is the main constituent of coral skeletons and mollusk shells, limestone, and chalk. calve To shed icebergs into the sea. See also icebergs. carapace The upper shell of a turtle; the protective outer covering of some other animals, such as crabs. carbon cycle The cycling of carbon through the environment. During the cycle, carbon exists in the bodies of living things, in carbon dioxide in the atmosphere and oceans, in fossil fuels, and in rocks such as limestone. cartilaginous fishes Fish, such as sharks, rays, skates, and chimaeras, whose skeleton is of cartilage, not bone. See also bony fishes. catadromous Of fish: living most of their lives in fresh water but migrating to the sea to breed. Eels are an example. See also anadromous. cephalopods A group of swimming mollusks that includes squid, cuttlefish, octopuses, and nautiluses. They have large brains and demonstrate complex behavior. See also mollusks. chemosynthesis A process in which some organisms make their own food using the energy from naturally occurring chemicals such as hydrogen sulfide. See also photosynthesis, autotroph, primary producer.

GLOSSARY chlorophyll The green pigment of plants and seaweeds that allows them to make their own food by using the Sun’s energy. See photosynthesis. chromatophore A skin cell in which the distribution of colored pigment can be altered, allowing an animal to change color. Color change may be fast, as in cephalopods, or slower, as in crustaceans and some fish. cilia Tiny beating hairlike structures on the surfaces of some cells. Used to aid movement in small organisms, or to create water currents. Singular cilium. cloaca The combined opening of the digestive, urinary, and reproductive systems of many vertebrates (e.g., fish, birds) and some invertebrates. cnidarians A major group (phylum) of invertebrate animals with simple bodies bearing tentacles that surround a single opening (mouth). Cnidarians include corals, anemones, and jellyfish, and are often colonial. Their two typical body forms are the polyp and the medusa. In some cnidarians, both forms occur during the life cycle. See also colonial, coral, medusa, nematocyst, polyp. coast See concordant coast, depositional coast, discordant coast, drowned coast, emergent coast, erosional coast, primary coast, secondary coast. cold seep A natural seepage of oil or other energy-containing chemicals on the sea floor, often supporting dense concentrations of marine life. colonial Of an animal: living in colonies. A colony can consist of separate individuals, as in the case of sponge shrimp, or animals joined by strands of living tissue, as in the case of many marine invertebrates, such as corals and bryozoans. Individuals may be specialized for different roles, such as feeding, reproduction, and defense, in which case the colony may behave like a single animal. See also bryozoans, cnidarians, zooid. comb jellies see ctenophores. commensal Living in close association with an organism of another species, for example, by sharing its burrow, without either helping or damaging it. See also mutualism, symbiosis. concordant coast Coast on which hills and valleys are roughly parallel to the shore, resulting either in a straight coastline or one with rocky islands running parallel to the shoreline. See also discordant coast. continental crust The material in Earth’s crust that forms the continents, including the continental margins. It is lighter and thicker than oceanic crust. continental margin A continent’s edge below sea level, including the continental shelf and continental slope. continental rise The gently sloping seabed around the edge of ocean basins that adjoins the bottom of the continental slope.

continental shelf The gently sloping seabed around the edges of most continents, formed of continental crust and averaging around 425 ft (130 m) deep. continental slope Sloping seabed at the seaward edge of the continental shelf. It descends relatively steeply to the continental rise. convection Circulating currents in a fluid—for example air, water, or hot rock—that result from heated portions rising because they are less dense, and sinking later as they cool. copepods Small, swimming crustaceans, usually less than 1/16 in (2 mm) long, that make up a large part of the zooplankton. There are also many parasitic and burrowing species. See also zooplankton. coral Any of various cnidarians that live fixed to the ocean bottom, secrete skeletons for support, and are usually colonial. The true corals lay down hard skeletons of calcium carbonate outside their bodies that eventually form coral reefs. Other coral groups include the sea fans. See also cnidarians, sea fans, zooxanthellae. coral bleaching Phenomenon in which coral animals lose their tiny symbiotic algae (zooxanthellae), usually in response to a stress in the environment. Bleached corals may later die. See also zooxanthellae. coral reef A rocklike, often ridgeshaped structure of calcium carbonate built in shallow tropical seas by generations of coral animals. See also barrier reef, fringing reef. coralline Resembling coral; mainly applied to red seaweeds that form hard, calcareous crusts on rocks or in coral reefs. Coriolis effect Phenomenon resulting from the rotation of Earth, in which winds and currents traveling toward or away from the equator are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The effect helps to explain the direction of prevailing winds and the existence of gyres. crabs see crustaceans. crinoids Stalked echinoderms, also called sea lilies, that filter-feed using their branching arms. Some species have no stalks and are known as feather stars. See also echinoderms. crustaceans The most diverse and abundant group of arthropods in the oceans. It includes crabs, lobsters, shrimps, barnacles, krill, copepods, isopods, and amphipods. Their jointed appendages are variously modified as claws, legs, swimming organs, or filter-feeding devices, depending on the species. See also arthropod. ctenophores Transparent jellyfish-like animals that hunt in the plankton. They swim using beating hairlike structures arranged in rows called comb plates. Also called comb jellies.

current Any sustained horizontal flow of water. See also drift, surface current, thermohaline circulation, turbidity current, western boundary current. cusp Any shape formed by two concave lines meeting at a point. Cusp-shaped ridges of sand are often created on beaches by wave action. cyanobacteria A group of minute, single-celled organisms, which can photosynthesize like plants. They are classified as bacteria, because they have a similar structure. Also called blue-green algae, although they are not closely related to other algae. See also photosynthesis. cyclone (1) Also called a depression, a pattern of circulating air in the atmosphere with low pressure at the center. Cyclones normally form over oceans outside the tropics and are associated with wet and windy weather. (2) See tropical cyclone.

D dark zone Vertical zone of the seabed and water column at around 3,300– 13,000 ft (1,000–4,000 m), between the twilight zone and abyssal zone. Virtually no light penetrates this deep. See also abyssal, twilight zone. delta An often fan-shaped structure of sediment built by the deposition of material by a river at its mouth. demersal Of a fish: living mainly near the sea floor. deposit feeding Feeding by extracting food particles from mud or other deposits. See also filter feeding. depositional coast A coast that is growing seaward due to deposition of sand and other sediment supplied by rivers or ocean currents. See also emergent coast, erosional coast. detritus Fragments of dead organisms and organic waste material, often mixed with sediment or suspended in ocean currents. A detritivore is an animal that feeds on detritus. diatoms A group of plantlike protists that are part of the algae and major primary producers in the plankton. They are single-celled but often grow as chains or colonies. Diatoms secrete intricate cases of silica around themselves. See also algae, primary producer, protists. dimorphism see sexual dimorphism. dinoflagellates A group of protists that bear two flagella. They are common in ocean plankton. Some are animal-like (eating other organisms), while others are plantlike (photosynthesizing) and are therefore part of the alga. See also algae, flagellum, protists. discordant coast Coast on which hills and valleys are roughly at right angles to the shore, resulting in an indented coastline of headlands and bays. See also concordant coast. doldrums The region of very light winds close to the equator.

dorsal Relating to the back or upper surface of an animal. See also ventral. drift A broad, slow-moving flow of surface water; for example, the North Atlantic Drift. drowned coast A coast where the land has sunk or the sea level has risen compared with the previous level. It may show features such as rias or fjords. See also emergent coast, fjord, ria. dune A hill or ridge-shaped structure of sand formed by wind action along some coasts and in deserts. Coastal dunes are usually formed on low-lying land behind beaches.

E echinoderms A major group (phylum) of marine invertebrates that includes starfish, brittle stars, sea urchins, sea lilies, sea cucumbers, and sea daisies. Echinoderms have bodies arranged in parts rather like the spokes of a wheel (so-called “radial symmetry”). They have chalky protective plates under their skin, and use a unique system of hydraulic “tube feet” for moving, or for capturing prey, or both. echolocation Method of locating and characterizing nearby objects, used by dolphins, bats, and some other animals, by emitting high-pitched sounds and interpreting their echoes. echo-sounding The use of sound equipment to measure the depth of objects or the ocean floor; also used as a synonym for echolocation. See also sonar. eddy A circular motion of any size and speed in a fluid. Mesoscale eddies of more than 60 miles (100 km) across are important features of ocean circulation. In tidal currents and whirlpools, an eddy is a circular motion slower than a whirlpool. See also gyre, vortex, whirlpool. Ekman effect Tendency for a wind or current to cause air or water above or below it to move, but in a different direction to the original wind or current. The effect results from the rotation of Earth. At the ocean surface, the net result is usually that a prevailing wind creates a water current at 90° to the wind direction. See also Coriolis force. El Niño Phenomenon by which the waters of the eastern Pacific off South America become warmer than usual every 4–7 years. The opposite phenomenon, in which eastern Pacific waters are unusually cold, is called La Niña. The term El Niño is also used as shorthand for the larger phenomenon called the El Niño– Southern Oscillation. See ENSO. emergent coast A coast where the land has risen or sea level has fallen compared with a former level. See also drowned coast, isostasy. ENSO Used as an abbreviation for the El Niño–Southern Oscillation.

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GLOSSARY A worldwide variation in Earth’s climate pattern and ocean circulation, including the El Niño phenomenon, associated with a change in the position of warm surface waters in the eastern Pacific. erosional coast A coast that is being eroded by the action of the sea. Rocky coasts are typically erosional, but so are some low-lying, sandy coasts. See also depositional coast. estuary The mouth of a large river. Used more broadly, the term includes any bay or inlet where sea water becomes diluted with fresh water. eustatic Of sea-level changes: occurring worldwide simultaneously, for example, as a result of melting ice sheets. See also isostasy. eutrophication The altering of an aquatic ecosystem by the addition of plant nutrients, such as nitrate and phosphate. Often caused by humans, it can greatly change the character of an ecosystem by, for example, causing algal blooms. See also bloom. exoskeleton A skeleton on the outside of an animal’s body, often also acting as a protective barrier. Arthropods, such as crustaceans and insects, have an exoskeleton. See also arthropods.

F fast ice Sea ice forming a continuous sheet. See also sea ice, pack ice. fathom The traditional unit of depth measurement at sea, equivalent to 6 ft (1.83 m). fault A fracture in Earth’s crust where rocks have moved relative to one another either vertically or horizontally. feather stars see crinoids. Ferrel cell A large-scale circulation of air in temperate regions, involving air rising at around 60°N and S, flowing southward at a high altitude, descending at around 30°N or S, and returning north as the westerlies (westerly winds). See also Hadley cell. fertilization The union of a male and female sex cell (such as a sperm and an egg cell in animals) as the first step in the production of a new organism by sexual reproduction. Some marine animals release eggs and sperm into the sea to meet by chance (external fertilization), while in others, the male transfers sperm directly into the female’s body (internal fertilization). fetch The distance of open ocean across which a wind is able to blow, and across which waves generated by the wind are traveling. A longer fetch tends to result in larger swell waves. See also swell wave. filter feeding Feeding by collecting and separating food particles from the environment. When the food particles are suspended in water it is also called suspension feeding. See also deposit feeding.

fjord A narrow, steep-sided, deep inlet of the sea, once occupied by a glacier. Fjords have a shallower sill where they meet the open sea. See also ria. flagellum A flexible, microscopic, hairlike structure used for propulsion by some single-celled organisms and for creating a water current by sponges. It is longer than a cilium. Plural flagella. See also cilia, sponges. flatworms A major group (phylum) of invertebrates with simple, usually flattened bodies. Free-living forms are carnivorous; there are also many parasitic species, including tapeworms. fluke Either of the lobes forming a whale’s, dolphin’s, or dugong’s tail. foraminiferans A group of protists whose empty, chalky skeletons are a major part of some deep-sea sediments. They are animal-like (they feed on other organisms) and include both planktonic and bottom-living types. See also protists. forced wave A water wave created by storm winds at sea. Forced waves are taller and have a shorter wavelength than swell waves. See also swell wave. foreshore The part of a shoreline that lies between the average high- and low-water marks. See also tides. frazil ice Ice in the form of tiny crystals floating on or near the sea surface. It is the first stage in the formation of sea ice. See sea ice. fringing reef A coral reef just offshore, without an intervening lagoon or stretch of water. See also barrier reef. front A vertical or oblique region at the boundary of two masses of air or water with different characteristics.

G gabion A wire cage filled with stones. Gabions are used to protect coastlines artificially against erosion. gastropods The group of mollusks that includes snails, slugs, and pteropods (sea-butterflies). See also mollusks. gill rakers Projections on the insides of the gill supports of some fish that sieve particles entering their mouths. glacier An elongated mass of compressed ice that flows slowly downhill. Glaciers that reach the sea give rise to icebergs. grease ice Stage of formation of sea ice in which frazil ice crystals congeal to form a soupy texture. See also frazil ice, sea ice. greenhouse gas A gas, such as water vapor, carbon dioxide, or methane, that prevents heat from radiating from Earth, causing Earth’s surface to warm (the greenhouse effect). Some greenhouse gas emissions are natural; others are caused by human activities. groyne An artificial barrier built down a beach and into the sea to hinder

transport of materials by longshore drift. See also longshore drift. guyot A flat-topped submarine mountain, also called a tablemount. See also seamount. gyre A large-scale circulation of surface ocean currents, typically spanning a whole ocean. See also eddy.

H hadal Relating to the deepest oceanic regions below 20,000 ft (6,000 m), within ocean trenches; deeper than the abyssal zone. See also abyssal. Hadley cell A large-scale circulation of air in warmer regions, caused by warmed air rising near the equator, traveling to mid-latitudes, cooling and descending, and returning to the equator as the trade winds. halocline A boundary between waters of different salinities, across which salinity changes rapidly. See also pycnocline, thermocline. headland A promontory on a shoreline, usually high and rocky and under strong forces of coastal erosion. See also erosional coast. heat capacity The amount of heat energy that a given substance can absorb for a given rise in temperature. Water has a high heat capacity and so can act as a store of heat. hermaphrodite An animal that is both male and female. Animals that are both sexes at once are called simultaneous hermaphrodites. Others start as males then become females, or vice versa. Some species change sex repeatedly. holdfast A rootlike structure that anchors a seaweed to rocks but does not absorb nutrients like a true root. holoplankton Planktonic organisms that spend all of their life as plankton. See also meroplankton, plankton. holothurians Soft-bodied, sausageshaped echinoderms, also called sea cucumbers, that feed mainly by swallowing mud and detritus. Their radial symmetry is not obvious at first glance. See also echinoderms. hotspot A localized region of Earth that experiences large-scale upwelling of magma. As oceanic crust moves over a hotspot, a line of volcanic islands, such as the Hawaiian islands, may form over millions of years. hurricane (1) A name for a tropical cyclone, especially one occurring in the Atlantic. See tropical cyclone. (2) A wind speed greater than 72 mph (116 km/h). hydrocarbon Any chemical compound made only of carbon and hydrogen atoms. hydroids Cnidarians that grow as small, branching colonies of polyps attached to rocks or seaweed. Each polyp is specialized either for feeding,

reproduction, or sometimes for defense. See also cnidarians, polyp. hydrothermal vent A fissure in a volcanically active region of the ocean floor from which superheated, chemical-laden water emerges. The energy in the chemicals fuels rich biological communities via the activities of chemosynthetic bacteria and archaea. See also chemosynthesis.

I ice age Any episode in which Earth’s temperatures were much lower than today and ice cover more extensive. The Ice Age (with capitals) refers to a series of such episodes within the last 2 million years, the last ending around 10,000 years ago. iceberg A large fragment of ice calved from the end of a glacier or ice sheet that is in contact with the sea. See also calve. ice cap A mass of permanent ice similar to an ice sheet but smaller in extent. ice lead A channel of open water among sea ice. ice rafting Transport of rocky debris out to sea, frozen into icebergs. When the icebergs melt, the material is deposited as sediment. ice sheet A very large mass of permanent ice covering land, such as the Antarctic Ice Sheet. ice shelf An extension of an ice sheet into the ocean. Ice shelves are anchored to the sea floor at their landward end, but farther from the coast, they float on water. igneous rock Any rock that originates from the cooling of magma, such as basalt or granite. intermediate coast A coast whose features are intermediate between a primary and secondary coast. See also primary coast, secondary coast. internal wave A wave occurring at the boundary of two different layers of the same fluid rather than at the surface—for example, at the boundary between two layers of ocean water. intertropical convergence zone The region of air close to the equator where the north and south trade winds converge. invertebrate Any animal without a backbone, ranging from flatworms to spiders. Of a total of around 30 major groups (phyla) of animals, 29 are composed of invertebrates. irradiance The amount of radiation falling on a given area. island arc Chain of islands, usually including active volcanoes, created by the collision of the oceanic crust of two tectonic plates. One of the plates is subducted beneath the other, creating a trench on one side of the arc. See also subduction, ocean trench. isopods A group of crustaceans that usually have flattened bodies. The

GLOSSARY group is mainly marine but also includes the land-living woodlice. isostasy A state of equilibrium; applied especially to the relatively light rocks of the continental crust, which can be thought of as floating like icebergs among the heavier rocks of the ocean floor and mantle. Isostatic rebound is the tendency of land that was formerly ice-covered to rise slowly to its equilibrium level, often creating emergent coasts. See also continental crust, emergent coast. IUCN The initials still used to designate the World Conservation Union (formerly the International Union for the Conservation of Nature). This organization carries out conservationrelated activities, including gathering and publishing information on the current status of endangered species.

J jawless fishes Two groups of primitive fish called lampreys and hagfish, which branched off the line of fish evolution before jaws had evolved. jellyfish Cnidarians that typically drift among the plankton and catch prey using stinging tentacles. The body form of true jellyfish is a medusa. Some apparently similar forms such as the Portuguese man-of-war are not true jellyfish, but siphonophores. See also cnidarians, medusa, siphonophores.

K katabatic wind A wind that blows downward from an ice sheet, glacier, or cold valley, usually at night. krill Swimming, shrimplike crustaceans typically growing to ¾–22/3 in (2–6 cm) long, which form a large part of the zooplankton and an important link in the Southern Ocean’s food chain.

L La Niña see El Niño. lagoon A stretch of coastal water almost cut off from the sea by a spit or other barrier; also, the shallow water within the ring of an atoll. larva A young stage of an animal, especially when completely different in structure from the adult. The larvae of many marine animals, such as starfish, live as part of the plankton. See also metamorphosis. latent heat The heat absorbed or released when a substance changes its state—from gas to liquid, for example. The heat released when water vapor condenses is the main source of energy for hurricanes. latitude A position on Earth expressed in terms of its angle north or south of the plane of the equator. Low latitudes are those close to the

equator, while high latitudes are nearer the poles. levee A natural raised bank around some rivers, or an artificial bank built around a river or estuary. littoral Relating to the area of shore between high- and low-water marks. longitude A position on Earth expressed in terms of its angle east or west of an agreed line called the prime meridian circling Earth from pole to pole and passing through Greenwich, London, UK. longshore drift Process by which sediment is transported along a coast as a result of waves breaking at an oblique angle to the shoreline.

M magma Molten rock rising from deep inside Earth. mangrove Any of various trees growing on muddy shores in the tropics and adapted to live with their roots and lower trunks immersed in salt water. mangrove swamp Forestlike ecosystem formed by mangroves growing in muddy tidal areas and river mouths. Mangrove swamps only occur in the tropics and subtropics. mantle All the rock lying between Earth’s crust and its core. The mantle extends to a depth of about 1,800 miles (2,900 km). medusa One of the two main body forms of cnidarians. Medusae are wide and saucer-shaped, as well as usually free-floating and able to swim. A jellyfish is an example of a medusa. See also cnidarians, polyp. meroplankton Planktonic animals that are the larvae of animals that are not planktonic as adults, such as crabs. metamorphosis The process of transforming body form from that of the young (larval) form to a radically different adult form. It is common in marine invertebrates such as starfish, whose larvae live in the plankton but whose adults live on the sea floor. mid-ocean ridge A submerged range of mountains running along any part of the deep-ocean floor, marking the place where seafloor spreading is taking place. Also called a spreading ridge. See also seafloor spreading. mimicry Phenomenon in which one species of animal has evolved to look similar to another, unrelated animal. mixed layer The upper layer of the ocean that is kept mixed by winds and currents, so that its temperature and chemical characteristics are roughly uniform throughout. mollusks A major group (phylum) of invertebrate animals that includes the gastropods (snails and slugs), bivalves (clams and relatives), and cephalopods (octopuses, squid, cuttlefish, and nautiluses). Mollusks are soft-bodied and typically have hard shells, though

some subgroups have lost the shell during their evolution. mucus A sticky or slimy substance secreted by animals for protection, trapping prey, helping with movement, or other purposes. mutualism A close relationship between two different species in which both benefit.

N nanoplankton Planktonic organisms of 0.002–0.2 mm in diameter. Not as small as picoplankton. See also picoplankton, plankton. neap tide The tide with the smallest range within an approximately twoweek cycle, caused by the gravity of the Sun partly canceling out the effect of the Moon. See also spring tide, tides. nearshore The part of the shore affected by waves and tides under normal conditions. It includes the foreshore plus an area beyond whose bed is shallow enough to be stirred up by wave action. See also foreshore. nekton Animals of the open ocean that can swim strongly enough not to be at the mercy of ocean currents. Nekton include squid, adult fish, and marine mammals. See also plankton. nematocyst The coiled structure within the stinging cell of a jellyfish or other cnidarian that shoots out and injects toxin via a dartlike tip. See also cnidarians. nudibranchs see sea slugs.

O ocean basin A region of low-lying oceanic crust within which a deep ocean (or part of one) is contained, and usually surrounded by land or shallower seas. oceanic crust The type of Earth’s crust that forms the deep ocean bed. Made mainly of basalt, it is thinner, denser, and heavier than continental crust. ocean trench Elongated low-lying region of the ocean floor. Trenches are the deepest parts of the ocean. See also subduction. ooze Sediment on the deep ocean floor containing a large proportion of the remains of the skeletons of planktonic organisms, such as foraminiferans or radiolarians. overfall A stretch of rough water produced when a tidal current flows in the opposite direction to the wind. ovoviviparous Producing live young by retaining eggs so that they hatch while still in the female’s body.

P pack ice A mosaic of floating ice formed when continuous sea ice

is broken up by storms or waves. See also fast ice, sea ice. pancake ice Stage of formation of sea ice consisting of small flat areas of ice, curled at the edges where they bump into each other. pectoral fin Either of the front pair of fins in most fish and marine mammals, mainly used for steering but sometimes for propulsion. See also pelvic fin. pelagic Relating to or living in the waters of the open ocean, without immediate contact with the shore or the sea bottom. See also demersal. pelvic fin Either of the pair of fins located further back than the pectoral fins in most fish. See also pectoral fin. perennial Of plants: living for three or more years. pheromone An odor produced by an animal to communicate with others of the same species, to attract the opposite sex, for example. photic zone see sunlit zone. photophore A light-producing organ. photosynthesis Process in green plants, algae, and cyanobacteria whereby the Sun’s energy is used to build energy-containing food molecules from carbon dioxide and water. See also chemosynthesis, chlorophyll. phylum The highest-level grouping in the classification of the animal kingdom. Each phylum has a unique basic body plan. Mollusks, arthropods, and echinoderms are examples. phytoplankton Planktonic organisms, such as microscopic algae and cyanobacteria, which produce their own food by photosynthesis. picoplankton The smallest planktonic organisms, typically bacteria, of 0.0002–0.002 mm in diameter. See also nanoplankton. plankton Marine or freshwater organisms, living in open water, that cannot swim strongly and so drift with the currents. Although small life forms dominate, larger creatures, such as jellyfish, are also planktonic. See also nanoplankton, nekton, phytoplankton, zooplankton. plate boundary A border between two tectonic plates. The plates may be converging (destructive boundary), diverging (constructive boundary), or sliding past (conservative or strike-slip boundary). See also transform fault. plate, tectonic see tectonic plate. plate tectonics Phenomena linked to the relative movement of Earth’s tectonic plates, including continental drift, seafloor spreading, earthquakes, and mountain-building; also, the theory explaining these occurrences. polychaetes A large subgroup of segmented worms common in the oceans, often with bristles down the sides of the body. (Polychaete means “many bristles”). Some species can move around, while others anchor themselves within tubes or burrows

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GLOSSARY and filter-feed. See also segmented worm, tube worm. polynya An area of open water in an otherwise ice-covered sea, especially in the Arctic. polyp One of the two main bodyforms of cnidarians. An anemone or coral animal is a polyp. Polyps are typically tubular and attached to a surface at their base. See also cnidarians, medusa. prevailing wind A wind that tends to blow from a particular direction. See trade winds, westerlies. primary coast A coast whose features have not been significantly altered by marine erosion, the activity of animals such as corals, or human intervention. See also secondary coast. primary producer Often called simply a producer, an organism that makes food, using energy either from the Sun or from naturally occurring inorganic chemicals. See also autotroph, chemosynthesis, photosynthesis. productivity Rate at which living material is produced by organisms by growth and reproduction. See also primary producer. prokaryotes Organisms such as bacteria and archaea, whose cells are smaller and simpler in structure than the cells of animals, plants, and protists. Cells of prokaryotes have no nucleus. See also archaea, bacteria. protein A large molecule built by organisms from smaller molecules called amino acids. Proteins range from the enzymes that promote chemical reactions in body cells, to structural materials such as keratin— the tough protein that makes up hair, horn, and nails. protists A wide grouping of often unrelated, microscopic organisms, traditionally classified as a single kingdom. It includes mostly singlecelled forms, either animal-like (formerly called protozoa) or plantlike (many of which are termed algae). Some experts also include larger algae (seaweeds). Protist cells contain nuclei, like the cells of animals and plants, but unlike those of bacteria. pteropods Swimming, planktonic gastropod mollusks, also called sea butterflies. The crawling foot of their snail-like ancestors has evolved into muscular “wings” that propel them along. See also gastropod, plankton. pycnocline A boundary region in ocean waters within which density changes rapidly. It typically results from a combination of temperature and salinity levels, both of which affect density. See also thermocline.

R radiation The emission of high-energy particles or waves. Electromagnetic radiation consists of electromagnetic waves: listed from long-wave to

short-wave forms, these are radio waves, microwaves, infrared (heat) rays, visible light, ultraviolet light, X-rays, and gamma rays. Shortwavelength electromagnetic radiation has the highest energy. radiolarians Single-celled predatory organisms mainly living as plankton, often with a delicate, perforated, spherical skeleton. Radiolarian remains of are an important part of some oceanic sediments. reclamation The artificial conversion of a former coastal sea or wetland area into dry land. reef see coral reef. refraction The change of direction of a wave when it passes into a different medium—for example, light waves passing from air into water. Ocean waves are also refracted when they reach shallow water. respiration (1) Breathing. (2) Also called cellular respiration, the biochemical processes within cells that break down food molecules, usually by combining them with oxygen, to provide energy for an organism. See also anaerobic. revetment A sloping structure of spaced wooden or concrete beams, constructed to protect a beach or low cliff against erosion. ria A winding inlet of the sea, a drowned former river valley. Most present-day rias were created when sea levels rose at the end of the last ice age. Unlike a fjord, a ria was never occupied by a glacier. ribbon worms A major group (phylum) of narrow-bodied, unsegmented marine worms, also called proboscis worms, some of which can reach 160 ft (50 m) in length. rip current A current flowing away from a shoreline, carrying water that has been pushed shoreward by waves. See also tide rip. rip-rap Boulders piled deliberately on a shoreline to prevent erosion.

S salinity Degree of saltiness. salps Barrel-shaped, delicate-bodied tunicates that live as filter-feeders in the plankton. See also tunicates. salt marsh An ecosystem developing on sheltered, flat, muddy coastlines, where tidal flats are colonized by salttolerant land plants. See also tidal flat. sand dune see dune. scute Any of the horny plates that form the outer covering of the shells of turtles; also used to described a similar protective structure on some fish and other animals. sea arch A natural arch on a rocky shoreline, usually created by two sea caves on either side of a headland eroding into each other. sea butterflies see pteropods.

sea cave A cave created at the foot of a cliff by wave action. sea cucumbers see holothurians. sea fans Fan-shaped corals belonging to the gorgonian or horny coral group. Though often growing on coral reefs, they are not reef formers themselves. See also coral. sea pens A group of soft-bodied, colonial cnidarians. Each colony resembles a single individual, with one large, burrowing polyp anchoring the colony in seafloor mud, and smaller polyps feeding and reproducing. See also cnidarians, polyps. sea slugs Shell-less marine gastropods, often with bright colors and tufty gills (ctenidia) on their backs. Sea slugs are carnivores and are not closely related to land slugs. Also called nudibranchs. See also gastropods. sea stack An isolated pillar of rock left standing offshore on a rocky coastline after all the surrounding land has been eroded away. sea urchins A group of echinoderms, usually with a rigid case called a test, a globular body, long spines, and a downward-facing mouth. Most graze algae from hard surfaces, though the heart urchins and sand dollars are burrowers. See also echinoderms. seafloor spreading The creation of new oceanic crust by the upwelling of magma at mid-ocean ridges and consequent spreading of the sea floor on either side. See also plate tectonics. seagrasses Any of various plants able to grow and root in shallow, sandy seabed along coastlines, especially in warmer seas. Although not actually grasses, they are true flowering plants, unlike seaweeds, which are algae. sea ice Ice that forms on the surface of the sea, as distinct from ice shelves and icebergs, which originate on land. Some sea ice forms only in winter, while other sea ice is semipermanent. Sea ice forms and evolves in several stages. See frazil ice, grease ice, pack ice, pancake ice. seamount A submarine mountain, usually an extinct volcano. sea spiders A group of eight-legged predatory marine arthropods. It is not agreed whether sea spiders are closely related to land spiders or not. sea squirts see tunicates. seaweed A member of any of three main groups of large-bodied algae. Seaweeds can make their own food by photosynthesis, but they lack roots. Their classification is not agreed, but green seaweeds seem to be related to plants, while red and brown seaweeds may represent two unrelated lines of evolution. See also algae. secondary coast A coast with features significantly altered by marine erosion, the activity of animals such as corals, human intervention, or all three. See also primary coast. sedentary Of animals such as worms:

habitually staying in one position. See also sessile. sediment An accumulation of solid particles that have settled out from water; also used for deposits left by other agencies such as the wind. sedimentary rock Any rock originating from sediment that has later become compacted and hardened, such as sandstone. segmented worms A major group (phylum) of worms, also called annelids, whose body is built from repeating units (segments) each bearing copies of organs, such as kidneys. The phylum includes earthworms, plus many marine species, mostly within a subgroup called the polychaetes. See also phylum, polychaetes, worm. sessile Of an animal: attached permanently to a surface, especially without a stalk, and not able to move around. See also sedentary. sexual dimorphism Situation in which the males and females of a species differ in appearance, for example, in color, shape, or size. shrimp Any of various small, usually swimming crustaceans. True shrimps are relatives of crabs and lobsters. siphon In mollusks: a fleshy tubular extension of the body that aids the flow of oxygenated seawater to the gills or sometimes transports food particles for filtering. Cephalopods use their siphons for jet propulsion. See also cephalopods. siphonophores Floating, predatory, colonial cnidarians, such as the Portuguese man-of-war. The colony members have specialized functions but act together so that the colony functions like a single animal. See also cnidarians, colonial, polyp, zooid. sonar A method of echo-sounding; often used more broadly as a synonym for echolocation. See also echolocation, echo-sounding. Southern Oscillation see ENSO. spit A peninsula of sand or shingle or both created by longshore drift, usually at a point where the shoreline changes direction. See also bar, barrier island, longshore drift, tombolo. sponges A large group (phylum) of marine animals with a very simple structure that feed by creating currents through their bodies and filtering small particles from the water. They have no muscles or nerve cells, and sometimes no symmetry. spore (1) A tiny structure produced (usually in large quantities) by nonflowering plants, fungi, and some protists, from which a new individual can grow. Spores are much smaller than seeds and usually produced asexually, sometimes forming part of a complex life history. (2) The inactive, resistant form of some bacteria that helps them survive unfavorable conditions. See also asexual reproduction.

GLOSSARY spreading ridge see mid-ocean ridge. spring tide The highest high tide and lowest low tide within an approximately two-week cycle, caused by the Sun and the Moon being in positions in which their gravitational effects add together most strongly. See also tides, neap tide. squid see cephalopod. stack see sea stack. standing wave A wave that stays in the same position rather than moving along, found in particular situations such as tidal races. starfish A group of echinoderms, also called sea stars, having five or more “arms” (extensions to the body) and both mouth and anus on the underside. They swallow their prey whole, which can be very large for their size. See also echinoderms. storm beach The topmost ridge of sediment on a beach, usually formed by the highest spring tides in combination with storm conditions. See also berm, spring tide. storm surge A rapid rise in sea level caused by storm winds driving water toward a shoreline. It can cause disastrous coastal flooding, especially if occurring at the same time as a high spring tide. subantarctic Relating to latitudes immediately north of the Antarctic Circle. subarctic Relating to latitudes immediately south of the Arctic Circle. subduction The forcing down of oceanic crust belonging to one tectonic plate beneath another plate when two plates are colliding. Ocean trenches are the location of such subduction zones. sublittoral Relating to the coastal marine environment below the low-water mark. submersible A vessel built to operate underwater. Some submersibles are designed to be able to withstand great pressures in order to explore the ocean depths. sunlit zone The topmost layer of ocean water, where enough light penetrates for photosynthesis to occur. Also called the photic zone, it extends from the surface to up to 660 ft (200 m). See also dark zone, twilight zone. surf zone The zone on a shore where waves break and create foaming, turbulent water. surface current Any current flowing at the surface of the ocean—for example, the Gulf Stream. Surface currents are mainly caused by friction from prevailing winds. See also current, thermohaline circulation. surface tension The attraction between water molecules at a water surface, which creates a thin film with the strength to resist small deflections, allowing some insects, for example, to walk on the water surface.

suspension feeding see filter feeding. swash The movement of turbulent water up a shore after a wave breaks. The swash zone is the zone of a shore where swash typically occurs. swell waves Regular, smoothly traveling waves on the open ocean, especially when at a distance from the winds or storms that originally caused them. See also fetch. swim bladder A gas-filled organ in many fish, used to control buoyancy, and sometimes for other purposes such as sound production. symbiosis A close living relationship between two species, especially one in which both benefit. See also mutualism, commensalism.

T tablemount see guyot. tabular Of an iceberg: very wide and flat-topped. tectonic plate Any of the large rigid sections into which Earth’s crust and uppermost mantle are divided, whose relative movement is the subject of plate tectonics. The African Plate and the Pacific Plate are examples. See plate tectonics. terrigenous Of marine sediments: originating on the land (for example, carried to the sea by rivers). thermocline A region at a particular depth in the ocean or height in the air where average temperature changes rapidly. See also pycnocline. thermohaline circulation The part of the ocean’s water circulation powered by differences in the salinity and temperature of different water masses, rather than by the wind. Thermohaline circulation is the cause of most deep-water and some surface currents. See also surface current. tidal bore A single large wave created when an incoming tide moves up a narrowing channel, such as an estuary. tidal bulge or trough see tides. tidal current see tides. tidal flat A flat, muddy area covered at high tide; characteristic of sheltered areas such as estuaries. tidal race A strong current created when a tide-generated water flow moves through a narrow channel. tide rip A stretch of turbulent water where different tidal currents meet. tides Fluctuation in sea level resulting from the gravitational attraction of the Sun and the Moon on Earth’s oceans, combined with Earth’s own rotation. In the open oceans, each tidal cycle of just over 12 hours generates a small but measurable vertical rise (tidal bulge) and fall (tidal trough) in the water. Tidal effects are much more obvious near the coast, and lead to horizontal water movements (tidal currents) as well as vertical movements.

tombolo A spit linking an island to the mainland or another island. See spit. trade winds Prevailing winds blowing from the east toward the equator in subtropical and tropical latitudes. transform fault A fault in which the rocks on either side are displaced horizontally. Numerous transform faults occur at right angles to midocean ridges. See also plate tectonics. trench see ocean trench. tropical Relating to the warm regions of Earth that lie between the equator and the tropics of Cancer and Capricorn, at latitudes of 23.5° north and south, respectively. The term is sometimes used loosely for phenomena typical of these regions, even when occurring north or south of the two tropics. tropical cyclone A large-scale, circulating weather system in warmer latitudes, called by different names, such as hurricane and typhoon, in different parts of the world. It generates intense winds and torrential rain. Its energy comes from the water vapor rising from warm seas and then condensing. A less powerful version of the phenomenon is called a tropical storm. See also cyclone, hurricane, latent heat, typhoon. tsunami A sometimes huge water wave usually generated by displacement of water by an earthquake and capable of devastating shorelines thousands of miles from its origin. Sometimes inaccurately called a “tidal wave.” tube worms Worms that live anchored and protected in tubes, which are either secreted or built of material such as sand grains. Tube worms include the giant worms living around some hydrothermal vents, as well as many segmented worms. See also polychaetes. tunicates A group of mainly filterfeeding marine invertebrates closely related to backboned animals (vertebrates). There are both solitary and colonial species. They include non-moving attached forms (seasquirts) and others that drift in the plankton. See also salps. turbidity current A phenomenon similar to an underwater avalanche or landslide, involving water laden with sediments slipping down a slope. twilight zone The vertical zone of the water column and seabed lying between approximately 660 and 3,300 ft (200 and 1,000 m) deep, into which some light penetrates, but not enough to support photosynthesis. typhoon see tropical cyclone.

U upwelling The upward motion of deep-ocean water toward the surface. Some upwelling increases ocean fertility by recirculating nutrients from deeper layers.

V ventral Relating to the lower surface or belly of an animal. See also dorsal. vertical migration Behavior of many zooplankton, fish, and squid of the open ocean, in which they rise nearer the surface by night and sink deeper by day, probably to escape predators. vertical transport Any large-scale vertical flow of ocean water. vortex A fast-rotating eddy in a fluid; sometimes used as a synonym for whirlpool. See also eddy, whirlpool.

W water column The volume of water between the ocean surface and the bottom of the ocean. wave A motion or disturbance that transfers energy. The water in a wave crossing the open ocean does not move significantly except up and down as the wave passes. The high point of a wave is its crest and the low point its trough. Water motion becomes more complex and turbulent in waves breaking on shores (breakers). westerlies Prevailing winds that blow from the west. Westerlies are the most common winds in temperate regions. western boundary current A relatively narrow, fast-moving surface current formed at the western boundary of an ocean basin, usually as part of a gyre. The Gulf Stream is an example. Deep-water western boundary currents also exist. See also gyre. whirlpool A powerful eddy or vortex formed at the sea’s surface, often caused when two separate tidal currents meet. See also eddy, vortex. white smoker A deep-ocean hydrothermal vent in which the emerging hot water appears white because of light-colored mineral particles suspended in it. worm Any of a variety of usually nonswimming invertebrate animals that are long, slender and flexible, and lack legs and shells. See flatworms, ribbon worms, segmented worms, tube worms.

Z zoea The planktonic larval stage of certain crustaceans, including crabs. They are different in structure from their adult forms, having long spines. zooid An individual in a colony of interconnected animals, such as bryozoans. The term is not applied to colonial coral animals, which are termed polyps. See also polyp. zooplankton Any animals or animallike protists that are part of the plankton. See also plankton. zooxanthellae Symbiotic, microscopic algae living in the tissues of many corals. See also symbiosis.

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INDEX Page numbers in bold indicate feature profiles or extended treatments of a topic. Page numbers in italic indicate pages on which the topic is illustrated.

A abalone, red 284 Aberdeen Harbor, Hong Kong 99 Abrolhos Bank 442 Abudefduf saxatilis 360 abyssal plain 176, 177, 182 abyssal zone 168, 171, 219 Abyssobrotula galatheae 183 Acadia National Park 94 Acanthaster planci 309 Acanthephyra pelagica 296 acanthodians 227 accretion, cold 40 Acetabularia acetabulum 247 acidification, ocean 67 Acipenser sturio 340 Acklins Island 441 acoel flatworm 271 acorn barnacle 294 acorn worm 313, 314 Acropora hyacinthus 268 Actinia equina 266 Adamsia palliata 267 Adare Seamounts 485 Adare, Cape 483, 485 Adelaide Island 484 adelie penguin 379 Aden, Gulf of 422, 446, 448 Admiralty Island 459 Adocia species 259 Adriatic Basin 439 Adriatic Sea 120, 438 Aegean microplate 439 Aegean Sea 438, 439 Aegean Volcanic Arc 439 Aegir Ridge 430, 432 Aeoliscus strigatus 357 Aethia cristatella 399 Aethia pusilla 399 Aetobatus narinari 335 African Plate 423, 437, 438, 439, 442, 455 Africana Seamount 446 Agadir Canyon 437 Agalega Islands 454 Agassiz Fracture Zone 423, 457 Agassiz, Cape 484 Agattu Island 458 Aghulas Current 446, 447, 455 Aglaeophenia cupressina 262 Agulhas Basin 422, 446 Agulhas Plateau 446 Aipysurus foliosquama 375 Aipysurus laevis 375 air sacs, sea birds 378 Aitutaki 476 Ajo, Cabo de 437 Akademii Nauk Rise 461 Akademik Kurchatov Fracture Zone 436 Akpatok Island 426 Åland 433 Alaska Current 457, 459 Alaska Peninsula 459 Alaska Plain 457, 459 Alaska Seamount Province, Gulf of 459 Alaska, Gulf of 423, 457, 459 Alaskan brown bear 129 Alaskan mudflats 129

albatross black-browed 185, 201, 378, 387 black-footed 386 gray-headed 201 light-mantled sooty 386 short-tailed 386 wandering 387 albatrosses 380 albedo 46, 65 Albina, Ponta 443 Alboran Sea 438 Albula vulpes 341 Alcock Rise 450 Alcyonidium diaphanum 305 Alcyonium digitatum 264 Aldabra Atoll 158 Aldabra Group 454 Aleutian Basin 422, 457, 458 Aleutian Current 459 Aleutian Islands 422, 457, 458, 459 Aleutian Rise 458 Aleutian Trench 422, 457, 458, 459, 461 Alex Heiberg Island 425, 426 Alexander Archipelago 459 Alexander Island 483, 484 algae blue-green 233 green 248 mudflats 125 symbiotic partnership 248 algal bloom, Chesapeake Bay 116 Algarve 437 Algarve, Western, marine erosion 97 Algerian Basin 438 alginate extraction 151 Alix Seamount 455 all-terrain vehicles, effect on sand dunes 113 Allis Shad 344 Alosa alosa 344 Alpha Cordillera 424, 425 Alphecca Seamount 469 Alpine Fault, New Zealand 480 Altair Seamount 436 Alula-Fartak Trench 449 Aluterus scriptus 366 Alvarado Mangroves Ecoregion 132 Alvarado Ridge 479 alveolates 236 Alvin submersible 168, 171, 173, 182–83, 188 Alvinella pompejana 171, 275 Amalfi Coast, marine erosion 97 Amami-O-shima 464, 466 Amazon Estuary 118, 440 freshwater inflow 65 Amazon Fan 429, 442 Amazon, Mouths of the 442 Amblyrynchus cristatus 376 Ambulocetus 228 Amchitka Island 458 Amchitka Pass 458 America–Antarctica Ridge 423, 429, 482 American crocodile 132, 133, 377 American horseshoe crab 293 American lobster 313 Amirante Basin 454 Amirante Islands 454 Amirante Ridge 454 Amirante Trench 454 Ammodytes tobianus 364 ammonites 228, 229 Ammophila arenaria 109, 113, 251 Ampere Seamount 437 Amphibolis antarctica 150 Amphiprion ocellaris 360

amplitude, wave 76 ampullae of Lorenzini 323 Amsterdam Fracture Zone 447 Amsterdam Island 447 Amukta Pass 458 Amund Ringnes Island 426 Amundsen Gulf 424, 426 Amundsen Plain 423, 457, 483, 485 Amundsen Sea 423, 457, 483, 484 Amundsen Trough 424, 426 Amundsen, Roald (1872–1928) 426, 485 Amur River 65 Anadyr, Gulf of 457, 458 Anarhichus lupus 361 Anatolian Plate 439 Anaximander Ridge 439 Anchoveta, Peruvian 344 Andaman Basin 447, 450 Andaman Islands 447, 450 Andaman Sea 422, 447, 450 coral reefs 159 Andes Mountains 479 andesite 43 Andreanof Islands 458 Andrew Seamount 446 Andrew Tablemount 449 Andros Island 441 Anegada Gap 441 Anegada Passage 441 anemone Antarctic 267 beadlet 266 cloak 267 giant 266 jewel 143, 267 kelp 147 plumose 267 tube 177, 270 anemone shrimp 12–13, 296 anemonefish false clown 360 Maldives 218 angelfish, queen 154, 359 angelshark 323 angiosperms 146, 250 angler 222, 351 deep-sea 225, 350 hairy 350 humpback see common blackdevil Regan’s 351 Anglesey 432 Angola Basin 423, 429, 442, 443 Angria Bank 449 Anguilla anguilla 342 anhinga 132 anhydrite, hydrothermal vents 188 animals 256–57 bottom-living see benthos classification 207–209 diversity 256 reproduction 257 Anjouan 454 Anjuna Beach 111 Ankabna, Tanjona 454 Anna Trough 427 Anning, Mary (1799–1847) 228 Annobón 443 Anoplogaster cornuta 353 Anous stolidus 397 Anseropoda placenta 308 Antalya Basin 439 Antalya, Gulf of 439 Antarctic anemone 267 Antarctic Circumpolar Current 195, 201, 428, 444, 456, 482 Antarctic Coastal Current 201 Antarctic Convergence 201

Antarctic fur seal 403 Antarctic Ice Sheet 46, 482 Antarctic ice shelves 192–93 Antarctic krill 199 Antarctic Peninsula 423, 457, 483, 484 Antarctic Plate 423, 444, 445, 482 Antarctica 45 Antarctic Canyon 484 anthozoans 261 Antialtair Seamount 436 Anticosti, Île d’ 431 anticyclones 55 and downwelling 60 Antillean manatee 132, 133 Antilles 440 Antipathes pennacea 270 Antipodes Islands 481 Anton Bruun Ridge 454 Anurida maritima 304 Anvers Island 484 Aphrodita aculaeta 274 Aplysia punctata 286 Apogon aureus 359 Appendicularian 319 Aptenodytes forsteri 383 Aptenodytes patagonicus 382 Apulian Plateau 439 Aqaba, Gulf of 448 Arabian Basin 422, 447, 448, 449 Arabian Gulf 99 Arabian Peninsula 422, 446 Arabian Plate 423, 448 Arabian Sea 422, 447, 448, 449 Arafura Sea 422, 451, 456, 472, 473 Arafura Shelf 456, 472 Arcachon Lagoon, Cap Ferret 110 archaea 232, 233 archaeocyathids 227 archerfish, banded 131 Archipiélago de Camagüey 441 Archipiélago de Sabana 441 Arctic Basin, circulation 201 Arctic char 346 Arctic Ocean 424–25 circulation 200–201 deep-water 201 surface 200 currents 425 depth 169 formation 45 ocean floor 424 salinity 65 sea-ice 63, 199, 424 winds 425 Arctic tern, migration 220 Arctocephalus australis 403 Arctocephalus gazella 403 Ardea cinerea 390 Arenaria interpres 395 Arenas, Punta de 444 Arenicola marina 274 Argentine Basin 423, 429 Argo Fracture Zone 447, 455 Argyropelecus aculeatus 347 Aristotle’s lantern 307 Arnhem Land 472 Arnhem, Cape 472 Arothron stellatus 367 arthropods 290–92 anatomy 290 classification 208, 292 feeding 290 growth 291 lifestyle 292 reproduction 292, 294 Aru, Kepulauan 472 Aruba Gap 441

ASCAT 54 Ascension Fracture Zone 423, 429, 443 Ascension Island 185, 442, 443 Ascophyllum nodosum 239 Asia 425 asthenosphere 42 Astra racing yacht 57 Astrid Ridge 429 Astrobranchion adhaerens 309 Atacama Trench see Peru–Chile Trench Atafu Atoll 476 Atia 476 Atka Island 458 Atlantic cod 348 Atlantic Conveyor 61, 62–63, 430 Atlantic flyingfish 352 Atlantic guitarfish 333 Atlantic herring 344 Atlantic jackknife clam 281 Atlantic mackerel 365 Atlantic Ocean 428–31 central 442–43 circulation 428 depth 169 east 437 icebergs 195, 428 north 430 northwestern 431 ocean floor 428 opening 45 temperature 31, 34 water density layers 35 winds 428 Atlantic Plate 440 Atlantic puffin 399 Atlantic Ridley turtle 371 Atlantic sailfish 365 Atlantic salmon 346 Atlantic saury 352 Atlantic thorny oyster 280 Atlantic torpedo 334 Atlantic–Indian Basin 422, 429, 446 Atlantic–Indian Ridge 423, 429, 446, 482 Atlantis Fracture Zone 429, 436 Atlasov Island 460 atmosphere, Earth 41, 43, 226 atmospheric cells 54 atmospheric circulation 54 Atol das Rocas 442 atoll formation 152 atoll, raised 158 Atrolium robustum 319 Attu Island 458 ATVs see all-terrain vehicles Auckland Islands 481 auklet crested 399 least 399 auks 380 Aulostomus maculatus 356 Aurelia aurita 262 Austral Fracture Zone 477 Australes, Îles 476 Australia, southeast 480 Australian giant cuttlefish 289 Australian pelican, Coorong Lagoon 121 Australian Plate 423, 446, 451, 472, 473, 480 Australian sea lion 404–405 autonomous underwater vehicle 187, 485 autotomy 286 Aves Ridge 441 avocet, pied 394 Awaji Island 83 ayre see tombolo

INDEX Azores 185, 423, 436, 437 Azores Plateau 436, 437 hotspot 437 Azores–Biscay Rise 429, 436, 437 Azov, Sea of 439

B Bab el Mandeb 448 backshore 106 bacteria 232, 233 Baffin Basin 423, 425, 426, 429 Baffin Bay 195, 423, 425, 426, 428 Baffin Island 423, 426 Bagre marinus 345 Bahama Banks 156 Bahama Basin 441 Bahama Escarpment 441 Bahamas 440 Pink Sands Beach 108 Bahia Seamount 442 Bahía, Islas de la 440 Baja California 469 Baker Island 476 Bakutis Coast 485 Balabac Strait 465 Balaena mysticetus 408 Balaenoptera acutorostrata 409 Balaenoptera musculus 412 Balearic Basin 438 Balearic Islands 438 baleen 412 Bali 451 Bali Sea 451 Balistoides viridescens 366 Ball’s Pyramid 481 ballan wrasse 142 Balleny Islands 456, 483, 485 Balleny Seamounts 485 Baltic Sea 119, 429, 432, 433 depth 169 wind farming 434, 435 Baltica 44 bamboo, sea 148 Bamburgh Beach, tidal range 79 Banaba 467, 473 Banâs, Râs 448 Banc d’Arguin 110 Banda Sea 422, 451, 456, 465, 466, 472 banded archerfish 131 banded coral shrimp 217 banded snake eel 343 banded-iron formation 43 bandfish, red 359 Bangka, Pulau 451, 465 Bangladesh, sea-level rise 91 bank reefs 152 Banks Island 423, 424, 426, 473 Banks Peninsula 481 Banks Rise 424, 426 Banks Shelf 424, 426 bannerfish, longfin 160, 161 Banzare Seamounts 447, 483 bar, baymouth 93 Baranof Island 459 Barbados Trough 441 barbels 345 beluga sturgeon 340 gafftopsail sea catfish 345 nurse shark 323 barchans, Curonian Spit 119 Barclays Adventurer racing yacht 57 Barcoo Tablemount 481 Bardin Seamount 454 Barents Plain 425 Barents Sea 422, 425, 427 phytoplankton bloom 427 Barents Trough 425, 427 Barentsøya 425, 427 Barmade Bank 433 Barnacle Acorn 294 Gooseneck 294 barnacles 292

Barra, Sound of 148 Barracuda Fracture Zone 423, 429 Barracuda Ridge 441 Barracuda, Great 365 Barrel Sponge 260 barrel waves 28–29 barrel-eye 345 barrier islands 93 Hatteras Island 95 Barrier Reef 440 barrier reefs 152 barriers, tidal 105 Barrow Island 451 Barrow, Point 424 basalt 42, 48 Giant’s Causeway 95 Bashi Channel 465, 466 basins, sedimentary 45 basket stars 306 basking shark 170, 328 Bass Strait 112, 447, 456, 480 Bassas da India 454 Bassas de Pedro Bank 449 basslet, orange fairy 162–63 Batabano, Golfo de 441 Batavia Seamount 447, 451 batfish, polka-dot 350 Bathurst Island 424, 426, 472 Bathurst, Cape 424, Bathypterois grallator 347 Batterbee, Cape 483 Bauer Basin 423, 457, 479 Bauer Fracture Zone 479 Bauer Scarp 479 Bauld, Cape 431 Bay of Bengal 134, 450 Bay of Biscay 437 Bay of Fundy 80, 126, 431 mud-shrimp 126 salt marsh 124 Bay of Pigs 133 Baydaratskaya Guba 425 baymouth bar 93 Bazaruto Achipelago 158 Bazaruto, Ilha do 454 beach black volcanic 112 dissipative 106, 108 Cox’s Bazar Beach 111 Jeffreys Bay 110 Ninety Mile Beach 112 drift-aligned 106 embayed 106, 112, 113 Anjuna Beach 111 gravel 107 olivine crystals Mahana Beach 470–471 pocket 106, 109, 112 raised 89, 96 reflective 106, 107 storm 109 swash-aligned 106 beach cusps 106 beach face 106 beach morning-glory 252 beach nourishment 105 beach plants 242 beaches 106–107 composition 107 types 106 zones 106 beadlet anemone 266 Beagle Channel 444 beaked sea snake 374 bear Alaskan brown 129 polar 25, 199, 402 threat of global warming 91 Bear Peninsula 484 Beata Ridge 441 Beaufort Gyre 200, 425 Beaufort Island 485 Beaufort Sea 423, 424, 426 Beaufort Shelf 424 Beaufort Slope 424 bee hummingbird 133 bee, dune snail 304 beetle, intertidal rove 304 Beggiatoa species 232

Behaim Seamount 484 Belém Ridge 442 Belgica Bank 425, 427 Belgrano Bank 484 Belitung, Pulau 451, 465 Belize Barrier Reef 133 Belize coast mangroves 133 Belle Île 437 Belle Isle 431 Belle Isle, Strait of 431 Bellingshausen Island 445 Bellingshausen Plain 423, 457, 483, 484 Bellingshausen Sea 423, 457, 483, 484 Bellona Plateau 473, 481 Bellona Valley 480, 481 beluga sturgeon 340 beluga whale 116, 199, 413 migration 221 bengal tiger 134 Bengal, Bay of 422, 447, 450 Benguela Current 59, 98, 148, 428, 442, 443 Benham Plateau 465, 466 Benin, Bight of 443 benthos 216–217 burrowing 217 fixed 216 mobile 216 symbiosis 217 Bering Canyon 458 Bering Sea 422, 424, 456, 457, 458, 461 Bering Strait 201, 422, 424, 457, 458 Beringa, Ostrov 458 Beringia land bridge 46 Berkner Bank 484 Berkner Island 483, 484 berm 106, 107 Bermuda Platform 156 Bermuda Rise 429, 441 Biafra, Bight of 443 Bib 348 Big Sur, tectonic uplift 103 bigeye jack see bigeye trevally bigeye trevally 360, 362–63 bigfin reef squid 279 bignose unicornfish 364 Bikini Atoll 161, 467 bill adaptation, sea birds 378 Bill Baileys Bank 430, 432 Bioco, Isla de 443 biodiversity continental shelves 140 coral reefs 154–55, 211 Shiraho Reef 160 hotspots 211 Loch Carron 211 Saba Bank 211 sea-ice 199 seagrass beds 146 seamounts 175, 211 biogenic sediment 180 bioluminescence 36, 224–25, 233, 263 common piddock 281 deep-sea cucumber 312 disguise 224 light production 224 lures 225 stoplight loosejaw 347 vampire squid 289 biomass pyramid 212 bioturbation, mud 313 birds 378–80 anatomy 378 breeding 209, 380 classification 209, 380 feeding 379 habitat 378 migration 380 birds of prey 380 Birgus latro 297 Biscay Plain 429, 437 Biscay, Bay of 437 Biscoe Islands 484 Bismarck Archipelago 466 Bismarck microplate 423, 472

Bismarck Sea 422, 456, 466, 472 bivalves 279 anatomy 276 feeding 278 movement 277 Bjørnoya 425, 427 Bjornöya Bank 425, 427 Black Coast 484 black mangrove 130, 132, 135 Black Sea 422, 429, 439 Black Shields 255 black skimmer 398 black smokers 188, 478 black tar lichen 255 black tufted lichen 255 black-browed albatross 185, 201, 378, 387 black-footed albatross 386 black-hawk, common 133 black-legged kittiwake 397 black-lip pearl oyster 280 black-winged stilt 394 blackdevil, common 351 blackdragon, Pacific 347 blackfin icefish 361 Blake Abyssal Plain 441 Blake Basin 441 Blake Escarpment 441 Blake Plateau 428, 441 Blake Spur 441 Blake-Bahama Ridge 441 Blanc, Cap 438 bleaching coral 153, 158, 159, 160, 161 effect of El Niño 68 Bledius spectabilis 304 blenny spiny-headed 16–17 tompot 364 blindfish, gelatinous 183 bloom algal, Chesapeake Bay 116 plankton 33, 37, 164, 169, 427 blubber 400 blue buttons 262 blue mussel see common mussel blue ridge coral 160 Blue Ridge Seamount 465 blue shark 332 blue swimming crab 301 blue whale 412 migration 417 blue-footed booby 391 blue-green algae 233 blue-rayed limpet 147, 148 blue-ringed octopus 288 blue-spotted stingray 334 bluecheek butterflyfish 359 bluestripe snapper 161, 359 blunt-nosed chimera see spotted ratfish bluntnose sixgill shark 325 Bo Hai 464 Bobaomby, Tanjona 454 bobbit worm 274 Bode Verde Fracture Zone 429, 442, 443 Bogorov Seamount 461 Bohadschia graffei 312 Bohai 464 Bohai Wan 464 Bohol 465, 466 Bohol Sea 465, 466 boiler reef 156 boiling point, water 31 Boknafjorden 433 Bolbometopon muricatum 361 Bollons Tablemount 457, 481, 483 Bon, Cap 438 Bonaire 441 Bonaire Basin 441 Bonaparte Seamount 443 Bone Basin 451, 472 Bone, Teluk 451, 472 bonefish 341 Bonellia viridis 314 bonin petrel 388 Bonin Ridge 464, 466

Bonin Trench 456, 464, 466 booby blue-footed 391 brown 391 Boothia Peninsula 424, 426 Boothia, Gulf of 424, 426 bootlace worm 273 Bora-Bora 476 Bora-Bora, Society Islands 88, 92, 161, 456 Borchgrevink Coast 485 Borden Island 424, 426 Borden Peninsula 426 Boreas Plain 425, 427 bores see tidal bores boring sponge 217 Borneo 422, 451, 456, 465 Bornholm 433 Bosporus 439 Bothnia, Gulf of 427, 433 Botryllus schlosseri 319 bottom-living animals invertebrates 313 see also benthos Bougainville Island 473 boundary currents 59 Bounty Islands 481 Bounty Trough 481 Bowers Bank 458 Bowers Basin 458 Bowers Ridge 458 Bowers Seamount 458, 459 bowhead whale 408 box jellyfish 264 boxfish, spotted 366 Brabant Island 484 brachiopods, Cambrian 227 Brahmaputra delta 134, 450 brahminy Kkite 393 bramble shark 323 Branchiostoma lanceolatus 319 Bransfield Strait 444, 484 Branta bernicla 381 brant goose 150, 381 Brazil Basin 423, 429, 442 Brazil Current 59, 428, 442, 444 breadcrumb sponge 259 breakers plunging 77; see also barrel waves; tube waves spilling 77 breakwaters 105 breezes, offshore and onshore 55 Breidhafjördhur 430 bristletail shore 304 sea 304 bristleworms 274 Bristol Bay 457, 459 Bristol Channel 432, 437 Britain 423, 425 brittlestar common 309 mangrove 131 brittlestars 177, 306 broad fish tapeworm 272 Brodeur Peninsula 424, 426 Broken Ridge 422, 447 Brosme brosme 349 brown bear, Alaskan 129 brown booby 391 brown noddy 397 brown pelican 214, 379, 380, 391 brown seaweeds 238–39 brown sargassum 235 Bruce Ridge 445, 484 Brunt Ice Shelf 484 brush-turkey, red-billed 135 Bryan Coast 484 Bryopsis plumosa 246 bryozoan gelatinous 305 pink lace 305 bryozoans 305 bubble shell 286 Buenos Aires 118 Bufoceratias wedli 350 Buka Island 473 bull kelp 150, 151 Bulldog Bank 454

495

496

INDEX bullhead shark 323 bullhead, long-spined 357 Bullina lineata 286 Bunce Seamounts 449 Buorkhaya Guba 425 buoyancy animals 256 fish 337 Burdwood Bank 444, 445 Burke Island 484 Burks, Cape 485 Burma Plate 450 Buru, Pulau 451, 465, 466, 472 bushy black coral 270 butterflyfish bluecheek 359 milletseed 161 button mangrove 130 by-the-wind sailor 214 Bylot Island 425, 426 Byramgore Reef 449 byssus threads 280

C C-Quester submersible 173 Cabo de Gata 438 Cabo San Juan 443 Cabot Strait 431 cactus seaweed 247 Cadiz, Gulf of 437 Calabar Canyon 443 Calappa angusta 297 Calarca Bank 441 calcareous ooze 180, 181 calcium carbonate 67, 180, 181 compensation depth 181 sclerites 260 calcium, in seawater 32 Calidris alpinus 395 California Current 58, 59, 66, 457 California, Gulf of 457, 469 California, temperature 31 California sea lion 403 Callorhinchus milii 324 Callorhinus ursinus 403 Calothrix crustacea 233 calving, iceberg 192, 195 Cambrian ocean life 227 plate tectonics 44 Camões Seamount 449 camouflage bony fish 338 photophores 36, 224 Campbell Island 480, 481, 457 Campbell Plateau 422, 457,480, 481, 483 Campeche Bank 440 Campeche Canyon 440 Campeche Escarpment 440 Campeche, Bay of 440 Canada Basin 423, 424, 426 Canada Plain 424 Canaries Current 428, 440, 442 Canary Basin 436 Canary Islands 423, 437 Canaveral, Cape 441 Cancer pagurus 300 Cancun 132 candy stripe flatworm 271 Canisteo Peninsula 484 Canterbury Bight 481 Canton City see Guanghzou canyon submarine 176 Monterey 469 Cap Ferret 110 Cape Basin 423, 429 Cape Bathurst, Cape 426 Cape Breton Island 431 Cape Cod 431 salt marshes 126 Cape Creus 96 Cape Hatteras 95 lighthouse 95 Cape Horn 444

cape penguin see jackass penguin Cape Prince Alfred 424, 426 Cape Verde Basin 423, 429 Cape Verde Islands 423 Cape Verde Plain 429 Cape Verde Terrace 429 Cape York Peninsula 472 capelin 345 Capelinhos volcano 437 capillary waves 76 Caranx sexfasciatus 360 Carapus acus 349 carbon cycle 67 carbon dioxide early Earth 43 in oceans 67 in seawater 32, 33 carbon sink 33, 67 carbonates, continental shelf 141 Carboniferous, plate tectonics 44 Carcharius taurus 328 Carcharodon carcharias 329 Carcinus maenas 300 Cardigan Bay 432 cardinalfish 131, 135 ring-tailed 359 Cardno Tablemount 443 Caretta caretta 370 Cargados Carajos Bank 454 Caribbean Plate 440 Caribbean reef shark 229 Caribbean Sea 423, 428, 440, 441, 478 depth 169 Caribbean spiny lobster, migration 220 Carlsberg Ridge 185, 422, 447, 448, 449 carnation coral 265 Carnegie Ridge 478 Caroline Islands 456, 466 Caroline Plate 423, 472 Caroline Ridge 466 Carpentaria, Gulf of 472 carpetshark 323 Carpilius maculatus 300 Carpophyllum flexuosum 150 carrageen moss see Irish moss carrageenan 245 cartilaginous fish 322–23 caruncles 312 Caryophyllia smithii 269 Carysfort Reef 156 Cascadia Basin 457, 459 Caseyr, Raas 446, 449 caspian tern 397 Cassiopea andromeda see Cassiopea xamachana Cassiopea xamachana 264 cassiterite, Andaman Sea 450 Casuarina 243, 253 Casuarina equisetifolia 253 catamarans, ocean yacht racing 57 catastrophe, iron 40 catfish 339 gafftopsail sea 345 striped 256, 345 Catoche Tongue 440 Catshark, Chain 329 Caucasus Escarpment 439 caudofoveates 279 Caulerpa racemosa 247 Caulerpa taxifolia 247 Caulophryn jordani 350 caves 93 as habitat 143 caviar 340 cavoline, three-tooth 286 Cavolinia tridentata 286 Cay Sal Bank 441 Cayman Ridge 441 Caymen Trench 169, 441 cays, Caribbean Sea 440 Ceara Plain 429, 442 Ceará Ridge 442 Cebu 465, 466 Cedros Trench 457, 469 Cedros, Isla 469 Celebes 422, 451, 456, 465, 466, 472

Celebes Basin 465, 466 Celebes Sea 422, 456, 465, 466 cells atmospheric 54 convection 41, 42, 44, 48 Ferrel 54 Hadley 54 Langmuir 61 polar 54 Celtic Sea 432, 437 Celtic Shelf 429, 432, 437 Cenozoic, ocean life 228 Central Atlantic Ocean 442–43 Central Basin Trough 465, 466 Central Bay, San Francisco 123 Central Kara Plateau 425 Central Pacific Basin 422, 457, 476 Central Slope 440 cephalopods 279 anatomy 276 chromatophores 277 feeding 278 movement 277 reproduction 279 Cepola macrophthalma 359 Ceram Sea 465, 466, 472 Cerastoderma edule 281 cerata, Polybranchid 286 Cerianthus membranaceous 270 Ceryle rudis 399 Cestium veneris 317 cetaceans 400–401 Cetorhinus maximus 328 Ceylon Plain 422, 447, 450, 451 Chaenocephalus aceratus 361 Chaetoceros danicus 237 Chaetodon semilarvatus 359 Chaetognatha 317 Chagos Archipelago 447, 455 Chagos Bank 455 Chagos Trench 447, 455 Chagos–Laccadive Plateau 422, 446, 447, 448, 449, 455 Chain catshark 329 Chain Fracture Zone 429, 442, 443 Chain moray eel 342 Chain Ridge 446, 449 chalk, erosion, White Cliffs of Dover 96 Chalkidiki 439 Challenger Deep 171, 456, 467 Challenger Fracture Zone 423, 457 Challenger Plateau 480, 481, 483 Challenger, HMS 171 champignon (mushroom rock) 158 Changjiang Estuary see Yangtze Estuary Channel Islands 432, 437, 469 Chanos chanos 344 Chao Phraya River, discharge into South China Sea 465 Chapman, Cape 424, 426 char, Arctic 346 Charcot Island 484 Charcot Seamounts 437 charge imbalance 30 Charlie-Gibbs Fracture Zone 423, 429, 436 Charonia tritonis 285, 309 Chatham Islands 457, 481 Chatham Rise 457, 480, 481, 483 Chauliodus sloani 346 Chaunax endeavouri 351 Cheetham, Cape 485 Cheilopogon heterurus 352 Cheju Strait 464, 466 Cheju-do 460, 464, 466 chelicerates 292 Chelidonichthys cuculus 358 Chelonia mydas 112, 370 chemistry, seawater 32–33 Cherbaniani Reef 449 Chesapeake Bay 114, 116, 431 Cheshskaya Guba 427 Chesil Bank 109 Chesil Beach 109

Chichagof Island 459 Chidley, Cape 426 Chilara taylori 349 Chile Basin 423, 457, 479 Chile Rise 423, 457 Chile Trench 444 Chile, fiordlands 103 Chimaera monstrosa 324 chimera blunt-nosed see spotted ratfish plownose 324 chimeras 322–323 chimneys, hydrothermal vents 188 Chinese white dolphin 122 Chinook Trough 468 chinstrap penguin 383 Chionis alba 394 Chíos 439 Chirikof Basin 458 Chironex fleckeri 264 chirostylus crab 179 chiton, lined 289 chitons 279 Chlamydoselachus anguineus 325 chloride ions 32 chlorophyll plants 242 satellite measurement 187 chloroplasts 237, 248 Choiseul 473 Chondrus crispus 245 chop and swell waves 76 chordates, classification 209 Choyo Seamount 466 Christmas Island 451 Christmas Ridge 457, 476 Christmas tree worm 217, 275 chromatophores 288 cephalopods 277 chromists 234–235 chromodorid sea slug 286 Chromodoris lochi 286 chrysophyta 237 Chukchi Plain 424 Chukchi Plateau 424 Chukchi Sea 422, 424, 458 Chukotskiy Peninsula 424 Chukotskiy Poluostrov 458 Chukotskiy, Mys 458 Churchill Peninsula 484 Chuuk Islands 466 cichlid, Mayan 133 ciliates 236 Cilicia Trough 439 Ciona intestinalis 318 circulation atmospheric 54 effect of El Niño/La Niña 68–69 oceanic Antarctic ice shelves 193 Arctic Ocean deep-water 201 surface 200 Atlantic Ocean 430 Bay of Bengal 450 and climate change 46, 65 deep-water 61, 201 Langmuir cells 61 Southern Ocean 201 surface 58–59, 200 underwater 60–61 and water density 35 see also currents, ocean Circumpolar Current 46 creation 45 Cirrhipathes species 270 cladistics 206 Cladococcus viminalis 237 cladogram 206 Cladophora mirabilis 247 cladophora, giant 247 clam giant 276, 281, 282–83 Pacific razor 129 clapper rail 127 Clarence, Isla 444 Clarion Fracture Zone 423, 457, 469

Clarion Island 469 Clark Basin 441 classification 206–209 Clatsop Spit 93 clay sediment 180, 181 cleaner wrasse 361 Cleidopus gloriamaris 352 cliff, undercut 93 cliffs underwater 143 uplifted 89 climate change and Arctic Ocean salinity 65 Atlantic Conveyor 61, 62–63, 430 Gondwana breakup 46 Mesozoic 46 ocean circulation 46 and sea-level 45, 88 Clipper Round the World Yacht Race 57 Clipperton Fracture Zone 423, 457, 476 cloak anemone 267 cloud formation 64 satellite monitoring 187 von Karman vortices 52–53 clownfish 24, 217 Clupea harengus 344 cnidarians 260–61 anatomy 260 classification 261 reproduction 261 zooxanthellae 261 cnidocytes 260 CO2 carbon cycle 67 early Earth 43 in oceans 67 in seawater 32, 33 coastlines drowned 88 emergent 89 coasts 86–87, 92–93 artificial 92, 99 breezes 55 classification 92 defenses 105 fringing reef 92 marine-deposition 93 pollution 141 primary 92 and sea-level change 88–89, 92 secondary 92 volcanic 92 wave-erosion 93 Coats Island 426 Cobb Hotspot 459 coccolithophore 181, 237 coccoliths 237 Cochlearia officinalis 252 cockle, common edible 281 cockling, Morecambe Bay 127 Coco-de-Mer Seamounts 454 coconut palm 243, 253 Cocos Basin 422, 447, 450, 451 Cocos Islands 451 Cocos nucifera 253 Cocos Plate 423, 478 Cocos Ridge 478 cod Atlantic 348 overfishing 212 Cod, Cape 431 Codium fragile 246 Codium tomentosum 247 coelacanth 339, 340, 455 Indonesian 340 Coelenterata see cniderians Coeloplana astericola 317 coffinfish 351 coho salmon 346 migration 220 cold accretion 40 cold currents 66 cold seeps 189 cold-water coral 153, 179 Coleopa frigida 304 Coleroon Estuary 134

INDEX collared kingfisher 399 Colombian Basin 441 Colombian Trench 478 Colón Ridge 457, 478 colonial sea squirt 319 colonies, invertebrate 256 Colossendeis australis 293 color change, cuttlefish 277 color, sea 36, 37 Colpomenia peregrina 238 Colpophyllia natans 269 Columbia Bay 112 Columbia, Cape 425 Colville Ridge 481 Colvocoresses Reef 449 comb jelly creeping 317 predatory 317 comets, as source of water 43 commensalism 217, 292 sea-star shrimp 308 Committee Bay 424, 426 Commodore Reef 465 common black-hawk 133 common blackdevil 351 common bluestripe snapper 359 common bottlenose dolphin 123, 414 common brittlestar 309 common diving petrel 389 common dolphin 26–27, 414 common edible cockle 281 common eider 381 eiderdown 381 common fangtooth 353 common glasswort 250, 251 common jellyfish, larva 214 common limpet 284 common lobster 297 common loon 386 common murre 14, 378–79, 398 common mussel 280 common periwinkle 285 common piddock 281 common prawn 296 common seafan 265 common sea lavender 252 common sea squirt 318 common seal 404 common shelduck 381 common shore crab 300 larva 214 common skate 333 common sole 366 common squid 289 common stargazer 364 common tern 128 Comoro Basin 446, 454 Comoros 446, 455 compensation depth, calcium carbonate 181 Conception Bank 437 concretions, mineral, Moeraki Beach 112 Condylactis gigantea 266 Conger conger 342 conger eel 342 Congo Fan 429, 443 Congo River 443 Congo River estuary 114 Constantine, Cape 459 consumers 212 continental crust 42 continental drift 44–45 continental rise 177 continental shelf 140–41 geology 141 continental slope 176 convection cells, mantle 41, 42, 44, 48 convergent plate boundary 48 conveyor global ocean 61, 62–63, 430 see also Atlantic Conveyor Cook Inlet 459 Cook Islands 477 Cook Strait 481 Cook Strait, currents 79 Cook, Captain James (1728–79) 123, 445, 477

Cookie Cutter Shark 326 Coorong Lagoon 121 Copacabana Beach 108 copepod, cyclopoid 294 copepods 170 copper shark 213 Cora Diva Bank 449 coral blue ridge 160 bushy black 270 carnation 265 daisy 268 dendrophyllid 269 devonshire cup 269 fast-pulse 265 giant brain 269 hump 268 lophelia 178, 179, 269 Mediterranean red 266 jewelry 260 mushroom 269 mushroom leather 264 organ pipe 264 table 268 whip 270 coral reefs 138–39, 152–55 biodiversity 154–55 destruction 155, 160, 179 zones 154–55 Coral Sea 422, 456, 473, 480 Coral Sea Basin 456, 472 Coral Sea Islands 472, 480 coral shrimp, banded 217 coral weed 245 Coral Triangle 211 coralline sponge 259 Corallium rubrum 260, 266 corals bleaching 153, 158, 159, 160, 161 effect of El Niño 68 cold-water 153, 179 hurricane damage 71 reef-building 260–61 anatomy 260 stony 153, 158 warm-water 153 cordgrass saltmeadow 126 smooth 124, 126, 127 Cordilleran Ice Sheet 46 core, Earth 40–41 Corfu 439 Coriolis effect 54 water 58 wind 55, 70 cormorant great 393 guanay 380, 392 Cornish kelp forest 148 cornish sucker 352 Cornwallis Island 424, 426 Coronation Gulf 424, 426 Corryvreckan Whirlpool 81 Corsica 438 Corvo 436 Corynactis viridis 267 Coryphaena hippurus 360 Coryphaenoides acrolepis 349 Coscinodiscus granii 235 Cosmoledo Group 454 Costa Blanca 438 Costa Brava 438 Costa del Sol 438 Costa Verde 437 Côte d’Azur 438 Cotton’s seaweed 245 Couch’s goby 148 Coulman Island 485 Courland Lagoon 433 cow shark 323 cowrie, tiger 285 Cox’s Bazar Beach 111 Cozumel, Isla 440 crab blue swimming 301 chirostylus 179 common shore 300 larva 214 dungeness 123

crab cont. edible 300 ghost 301 hermit 134, 267 reef 297 horseshoe 290, 293 Hydrothermal Vent 189 Japanese spider 297 long-legged spider 300 nodose box 297 orange fiddler 301 pea 217, 300 porcelain 291, 297, 298–299 red, migration 302, 303 robber 158, 297 sand bubbler 290 spotted reef 300 velvet 292 crabeater seal 405 Crary Bank 485 Creagrus furcatus 396 creeping comb jelly 317 crested auklet 399 Cretaceous ocean life 228 plate tectonics 45 Cretan Trough 439 Crete 439 Crete, Sea of 439 Crimea Escarpment 439 Crimean Peninsula 439 crinoids, fossil 311 crocodile American 132, 133, 377 Cuban 133 estuarine 135, 377 Indo-Pacific 377 Morelet’s 132 Nile 134 saltwater 136–37, 369, 377 crocodiles 368–69 Crocodylus acutus 377 Crocodylus porosus 136–37, 377 crocus, sand 242 crofter’s wig 239 crown of thorns starfish 158, 161, 307, 309 Crozet Basin 422, 446 Crozet Islands 446, 482 Crozet Plateau 446 Cruiser Tablemount 436 crust Earth continental 41, 42, 44 oceanic 41, 42, 44, 48 crustaceans 292 Cruz, Cabo 441 Cryptocentrus cinctus 364 Cryptoclidus eurymerus 228 ctenidia 277 Ctenophora 317 Cuban crocodiles 133 Cuban gar 133 Cuban hutia 133 cuckoo wrasse 361 reproduction 338 cucumber deep-sea 312 edible sea 312 sea 144, 181, 223, 312 Culcita novaeguineae 308 Cumberland Peninsula 426 Cumberland Sound 426 Curaçao 441 Curonian Lagoon 119 Curonian Spit 119 currents ocean 45 Aghulas Current 446, 447, 455 Alaska Current 457, 459 Aleutian Current 459 Antarctic Circumpolar Current 195, 201, 428, 444, 456, 482 Antarctic Coastal Current 201 Arctic Ocean 425 Atlantic Conveyor 61, 62–63, 430

currents cont. Atlantic Ocean 428 Benguela Current 59, 98, 148, 428, 442, 443 boundary 59 Brazil Current 59, 428, 442, 444 California Current 58, 59, 66, 457 Circumpolar Current 46 creation 45 cold 66 East Greenland Current 59, 425, 427, 430 Equatorial Countercurrent 442, 446, 447, 451, 473, 477 Equatorial Undercurrent 442, 473 Falklands Current 444 Guiana Current 428, 442 Gulf Stream 31, 66, 428, 431, 440 Atlantic Conveyor 63 map by Benjamin Franklin 59 heat transfer 31, 58, 66 Humboldt Current 376, 456, 457, 478, 479 Indian Ocean 447, 451 interaction 59 Jan Mayen Current 427 Kuroshio Current 58, 59, 66, 456, 457, 459, 460, 464, 467 Labrador Current 59, 116, 195, 426, 431 Liman Current 150 Malvinas current 59 Mesozoic 46 North Atlantic Drift 59, 66, 427, 428, 430, 431, 432 Atlantic Conveyor 63 North Equatorial Current 428, 440, 446, 447, 456 Norwegian Atlantic Current 425, 432 Oyashio Current 59, 457, 460 Pacific Ocean 456, 457 Peruvian Current 66, 344, 457 South Equatorial Current 442, 446, 447, 451, 455, 456, 473, 477, 479 Southern Ocean 482 surface 58–59, 66 Transpolar Current 200, 201, 424, 425 Tsushima Current 150, 464 warm 66 rip 110 subsurface 60 tidal 79 turbidity 176 cushion star 308 cusk-eel, spotted 349 cuskeel 183 cuttlefish Australian giant 289 eggs 279 color change 277 Cuvier Basin 447, 451 Cuvier Plateau 447, 451 Cuvier’s beaked whale 413 cyanobacteria 226, 232, 233, 255 Cyclades 439 Cycliophoran 316 cyclones 52–53, 55, 70–71 East China Sea 464 Haiyan 72–73 Timor Sea 451 and upwelling 60 see also hurricanes cyclopoid copepod 294 Cyclopterus lumpus 358 Cyclozodion angustum 297 Cyerce nigricans 286

Cymbula compressa 148 Cyphoma gibbosum 285 Cypraea tigris 285 Cyprus Basin 439

D D‘Entrecasteax Islands 472 Dacia Seamount 437 Dahlak Archipelago 448 daisy coral 268 Daito Ridge 464, 466 Dallas Reef 465 Dalmatia 438 Damar, Kepulauan 472 Dampier Seamount 443 damsel fish see sergeant major Dana Fracture Zone 479 Danish Straits 432 Danube Cone 439 Danube delta 439 Danzig, Gulf of 433 Dao 465 Dao Phu 465 Dardanelles 439 Dardanus megistos 297 Darien mangroves 135 Darien, Gulf of 441 dark zone 168, 171, 219 Darnley, Cape 483 Darwin Mounds 179 Darwin, Charles (1809–82) 294, 444 Dasyatis americana 334–335 Davidson Bank 458 Davie Ridge 446, 454 Davis Coast 444 Davis Sea 483 Davis Seamounts 429 Davis Strait 423, 426, 429 Dawhat Sawqirah 449 De Soto Canyon 440 dead man’s fingers 216, 264 Dead Sea 439 Dead Sea, salinity 35 Dean Island 485 Deccan Traps 455 decompression, divers 35 Deep Flight submersibles 173 Deep Rover submersible 223 deep sea red prawn 296 deep-sea angler 225, 350 deep-sea cucumber 312 deep-sea habitat 222–223 food 223 pressure 222 see also abyssal plain; abyssal zone; dark zone deep-sea jellyfish 262 deep-sea sediment 180, 182, 223 Deepflight Super Falcon submersible 173 Deepsea Challenger submersible 173 defenses, coastal 105 Del Cano Rise 446 Delaware Bay 431 Delgada Fan 469 Delgado, Cabo 446, 454 Delphinapterus leucas 413 Delphinus delphis 414 Deltaworks, Netherlands, stormsurge barriers 105 Demerara Plain 423, 429 Dendronephthya species 265 Dendrophyllia species 269 dendrophyllid coral 269 Denmark Strait 423, 425, 429, 430 Denmark Strait 430 density, seawater 35 Denson Seamount 459 deposition, coasts 93 depression see cyclones depth oceans 169 satellite estimates 187 Dermochelys coriacea 113, 371

497

498

INDEX Derwent Hunter Guyot 481 Deryugina Basin 461 deserts, ocean 219 Desmarestia aculeata 238 Desventurados, Islas de los 479 Deutschland Canyon 484 Devil’s Hole 433 devil’s-claw, grand 253 Devon Island 425, 426 Devon Ria Coast 96 Devon Shelf 425, 426 Devon Slope 425, 426 Devonian ocean life 227 plate tectonics 44 Devonshire cup coral 269 dhows 449 Diadema savignyi 310 Diadema setosum 310 Diamantina Fracture Zone 447 diamond-backed terrapin 126 diamonds, Namibia 443 diatoms 169, 181, 234, 235 siliceous 33 Dickins Seamount 459 Dictyocha fibula 237 Diego Garcia 455 Diego Garcia Atoll 159 differentiation, Earth structure 40, 41, 42–43 Digul River 135 bioluminescence 225 sunlit zone 169 Diodon hystrix 367 Diomedea exulans 387 Diphyllobothrium latum 272 Dipterus batis 333 Dirk Hartog Island 451 discharge, river 32, 63, 65, 200, 424, 465 Discovery Basin 448 Discovery Tablemounts 429 dissipative beach 106, 108, 110, 111, 112 diurnal tides 78 divergent plate boundary 48 Divided Flatworm 272 diving (human) decompression 35 effect on environment 475 free 168 scuba 173, 475 tourism 475 Dixon Entrance 459 DNA 206, 226 archaea 232 Doberai 465 Dodecanese 439 dog whelk 284 dogfish shark 323 dogfish, piked 325 Dogger Bank 432, 433 doldrums 428, 457 Doldrums Fracture Zone 429 Dolicholaimus marioni 314 Dollerman Island 484 dolphin Chinese white 122 common bottlenose 123, 414 common 26–27, 414 Indo-European humpback 414 Irrawaddy 135 La Plata 118 long-snouted spinner 414 Risso’s 414 Dolphin and Union Strait 424, 426 dolphinfish 360 dolphins, echolocation 37, 400 Dominica Passage 441 Donegal Bay 432 Dongjin estuary 129 Dorchester, Cape 426 Doubtful Sound 123 Dover Strait 433 White Cliffs 96, 180 Dover, Strait of 433 downwelling 60 epicontinental seas 45 Greenland Sea 427

Drachiella spectabilis 245 Dragonfish 224 Drake Passage 423, 429, 444, 457, 482 Drake Passage 444, 482 Dreadnought Bank 450 drift-aligned beach 106 drift, continental 44–45 Dronning Maud Land 484 drowned valleys 88, 148 Ducie Island 477 duck, Magellanic flightless steamer 381 ducks 380 Dufek Coast 485 dugong 134, 150, 158, 401, 419 importance of seagrass 146 see also paddle weed Dugong dugon 419 Dumbo octopus 288 Dumont D’Urville Sea 483 Dumshaf Plain 425, 427 Dundee Island 444, 484 dune buggies, effect on sand dunes 113 dune snail bee 304 dunes see sand dunes Dungeness crab 123 Dungeness Spit (Washington State, US) 113 Dungeness, Punta 444 dunlin 395 Durdle Door 92 Durgin Seamount 459 Dustin Island 484

E eagle Singapore bald see Brahminy kite white-bellied sea 37 Eagle Ray 158, 160, 204 Earth atmosphere 41, 43 convection 41 differentiation 41, 42–43 formation 40–41 internal heat 40 origin of life 226 rotation 54 structure 41, 42–43 earthquakes 49 Gulf of California 469 Japan 460, 463 Peru–Chile Trench 479 East Atlantic red gurnard 358 East Australian Current 66, 456, 457, 480 East Azores Fracture Zone 429, 436, 437 East Black Sea Escarpment 439 East Cape 481 East Caroline Basin 456, 466 East China Sea 422, 456, 464, 466 East Falkland 444 East Greenland Current 59, 425, 427, 430 East Indiaman Ridge 447, 451 East Mariana Basin 456, 466 East Mexico Shelf 440 East Novaya Zemlya Trough 425, 427 East Pacific Rise 175, 185, 456, 478, 480 East Pacific Rise 423, 457, 469, 478, 479, 483 East Scotia Basin 429, 445, 482 East Scotia Ridge 445 East Sea 422 East Sea/Sea of Japan see 150, 460 East Sheba Ridge 449 East Siberian Sea 422, 424 East Tasman Plateau 480 East Thulean Rise 436

East Wind Drift 195 Easter Fracture Zone 423, 457, 479 Easter Island 457, 479 Easter Island Fracture Zone 479 eastern box turtle 126 Eastern Mediterranean 438 Eastern Scheldt Estuary 119 storm surge-barrier 104 Eastward Knoll 441 Eauripik Rise 466 Ebrié Lagoon 121 Ebro Fan 438 ecdysis 291 Echeneis naucrates 360 Echidna catenata 342 Echiniscoides sigismundi 316 Echiniscoides water bear 316 Echinoderes aquilonius 316 echinoderms 306–307 anatomy 306 classification 208, 306 defense 307 feeding 307 reproduction 307 Echinodiscus auritus 310 Echinus esculentus 310 Echninocardium cordatum 311 echolocation 37, 400 Ecklonia maxima 148 Ecklonia radiata 150 ecotourism 475 eddies 79 Edgeøya 425, 427 Ediacaran fauna 226 edible crab 300 edible sea cucumber 312 edible sea urchin 310 Edward VII Peninsula 485 eel banded snake 343 Chain moray 342 conger 342 European 342 gulper 343 ribbon 342 sand 364, 399 slender snipe 342 spotted garden 343 eelgrass 148, 150, 250 Eelpout 189 eels 339 migration 220 see also Sargasso Sea Efate 473 Egeria Fracture Zone 447, 455 Egmont, Cape 481 egret great 125 little 390 Pacific reef 390 reddish 132 egrets 380 Egretta garzetta 390 Egretta sacra 390 eider common 381 eiderdown 381 Eights Coast 484 Eirik Ridge 429 Ekman spiral 58 Ekman transport 58, 60 Ekman, Walfrid (1874–1954) 58 El Niño 68 Peru–Chile Trench 479 El Niño Southern Oscillation 34, 68, 456 electrons 30 elephant fish see plownose chimaera Elephant Island 444, 484 elephant seal 222 collecting salinity and temperature data 61 Northern 405 pressure adaptations 35 Eleuthera Island 441 Ellef Ringnes Island 426 Ellesmere Island 423, 425, 426

Ellsworth Land 483, 484 Elops saurus 341 Eltanin Fracture Zone 423, 457, 483 embayed beach 106, 111, 112, 113 Emiliania huxleyi 237 emperor penguin 190–91, 192– 93, 379, 383, 384–385 Emperor Seamounts 422, 457, 458, 461, 468 Emperor Trough 468 Emydocephalus annulatus 375 endemic species 218 Enderbury Island 476 Enderby Plain 422, 446, 483 Endurance Canyon 484 Endurance Fracture Zone 444 Endurance Ridge 445, 484 energy cycles 212 Enewetak Atoll 161, 467 English Channel 432, 433, 437 formation 96 English Coast 484 Engraulis ringens 344 Enhalus acoroides 149 Enhydra lutris 402 Enhydrina schistosa 374 Ensius directus 281 Entelurus aequoreus 356 Enteroctopus dofleini 288 Enteromorpha species 246 Entrada, Punta 444 Eocene, plate tectonics 45 epicontinental seas 45 Epinephelus tukula 358 Eptatretus burgeri 319 Eptatretus stouti 319 Equatorial Countercurrent 442, 446, 447, 451, 473, 477 Equatorial Undercurrent 442, 473 Eratosthenes Tablemount 439 Erben Tablemount 469 Eretmochelys imbricata 370 Erimo Seamount 461 erosion coastal defenses 105 wave 93, 96–97 erosion gully 176 Erromango 473, 481 Error Tablemount 449 Eschrichtius robustus 408 Espichel, Cabo 437 Espiritu Santo 473 Estados, Isla de los 444 estuaries 114–15 environment 115 formation 114 inverse 122 tectonic, San Francisco Bay 123 types 114 Ethmodiscus rex 237 Etmopterus spinax 326 Etna 438 Etolin Strait 458 Eubalaena glacialis 408 Euboea 439 Eucheuma cottonii 245 Eucrossorhinus dasypogon 327 Eudyptes chrysolophus 383 Eudyptula minor 383 Eugenia, Punta 469 eukaryotes 207, 226 Eulalia viridis 274 Euphausia superba 295 Euphrates see Tigris Euphrates Delta Euramerica 44 Eurasian oystercatcher 378, 394 Eurasian Plate 437, 438, 439, 448, 451, 460 Europa, Île 454 Europe 425 European eel 342 European otter 402 European oyster 279 European sturgeon 340 Eurythenes 223

Euxine Plain 439 Evadne nordmanni 293 Evans Strait 426 evaporation 64–65 inverse estuary 122 evaporites, continental shelf 141 Everard, Cape 480 Everglades 132–33 evolution, parallel 45 Exmouth Plateau 447, 451 Explorer Plate 459 Explorer Seamount 459 exquisite lined flatworm 272 extinction, mass 228, 229 Exuma Sound 441 Exuma Valley 441 Exxon Valdez oil spill 459 eyelight fish 352

F FAD see Fish Attracting Device Faeroe Bank 430, 432 Faeroe Gap 430, 432 Faeroe Islands 425 Faeroe Shelf 430. 432 Faeroe–Iceland Ridge 430, 432 Faeroe–Shetland Trough 425, 430, 432 Faial 436 Fair Isle 433 fairy prion 388 fairy tern see white tern Fakaofo Atoll 476 Falkland Escarpment 429 Falkland Islands 423, 444, 482 Falkland Plateau 429, 444, 445 Falkland Trough 444 Falklands Current 444 Falmouth Bay 148 false clown anemonefish 360 Falster 433 fan, outwash 176 fangtooth 171, 223 common 353 Fantgataufa 477 Faraday Fracture Zone 436 Farallon Plate 459 Farewell Island 484 Farewell, Cape 481 faros 159 Farquhar Group 454 Fartak, Ra’s 449 fast ice 198 fast-pulse coral 265 Fastnet Race 57 fault scarps 98 faults Red Sea Coast 98 transform 442 Faxaflói 430 feather star passion flower 311 tropical 311 feather stars 306 Fernando do Noronha Plain 442 Ferrat, Cap 438 Ferraz Ridge 442 Ferrel cells 54 Ferris Seamount 479 fetch 76 fiddler crab, ritual display 301 Fieberling Tablemount 469 Fifty Fathoms Flat, The 449 Fiji 422, 457 Fiji Plate 473 Fiji Plateau 473 Filchner Ice Shelf 484 Filchner–Ronne Ice Shelf 484 filefish, scrawled 366 Fimbul Ice Shelf 484 Finland, Gulf of 433 fins, fish 336 Fiordland 481 fiordlands, Chile 103 fiords 88, 114, 115, 140 Alaska 459 fire urchin 307

INDEX firefly squid 36, 224 first-year ice 198 fish anadromous 220 bony 336–39 anatomy 336 buoyancy 337 camouflage 338 classification 209, 339 hunting 338 protection 338 reproduction 337 senses 337 swimming 336 cartilaginous 322–23 anatomy 322 classification 209, 323 hunting senses 323 reproduction 323 catadromous 220 classification 209 jawless 209, 227, 318 lobe-finned 227 migration 220 vision 36 Fish Attracting Device 215 fish farming 336, 355 fish-eagle, Madagascar 134 Fisher Bank 432 Fisher Strait 426 fisheries continental shelf 140, 165 continental slope 176 Gulf of California 469 sand eel 165, 355, 399 fishing 355 bycatch 355 damage to deep-water reefs 179, 355 deep-sea 354 East China Sea 464 hazard to wildlife 355, 379 industrial 355 traditional 355, 451, 465 fishing cat 134 Fiske, Cape 484 Fisterra, Cabo 437 flaccid green seaweed 246 flagella 234 flame shell 144, 145 flamingo tongue 285 flamingo, greater 132, 133 flashlight fish 224 flatback turtle 371 flatfish 339 flatworm acoel 271 candy stripe 271 divided 272 exquisite lined 272 imitating 272 Thysanoon 272 flatworms 271 Fleet Lagoon, Chesil Bank 109 Flemish Cap 436 flesh sponge 259 flightless rail 158 Flint Island 476 floating objects, as habitat 215 floats, gas-filled 256 flooding, coastal defenses 105 Flores 436, 451, 472 Flores Basin 451, 472 Flores Sea 451, 472 Florida Escarpment 440 Florida Keys 441 Florida manatee 133 Florida Plain 440 Florida Reef Tract 156 Florida-Hatteras Slope 441 Florida, Straits of 441 flower urchin 307, 310 Flustra foliacea 305 Fly River 135 flyingfish, Atlantic 352 fog over cold currents 66 northern Chile 66 San Francisco 67 Skeleton coast 66, 98, 443

Fogo Island 431 Foncia racing trimaran 57 food chain 33, 212 food web 212 food-energy pyramid 212 food, at depth 223 football jersey worm 273 foraminifera 108, 181, 237 foreshore 106 Formentera 438 Fortune Bank 454 Four North Fracture Zone 442 Foveaux Strait 481 Fox Islands 458 Foxe Basin 426, 428 Foxe Channel 426 Foxe Peninsula 426 Fragum erugatum 111 Fram Basin 425 Franklin Island 485 Franklin, Benjamin (1706–90) 59 Franz Josef Land 422, 425, 427 Fraser Island 480 Fratercula arctica 399 frazil ice 198 Fred Seamount 446, 454 free diving 168 freezing point, seawater 35, 198 Fregata minor 390 French Frigate Shoals, near-atoll 161 Freshfield, Cape 485 freshwater global 64 inflow 65 Fria, Cape 443 Friesian Islands 433 frigatebird, great 380, 390 frilled shark 323, 325 fringes, coastal, biodiversity 140 fringing reef 152 Frobisher Bay 426 Frøya Bank 433 Fuerteventura 437 Fugløya Bank 425, 427 fugu see pufferfish Fukushima nuclear power plant 463 fulmar, northern 388 Fulmarus glacialis 388 Funafuti 473, 476 Funafuti Atoll, sea-level rise 91 Fundy, Bay of 431 fungi 254 Fungia scruposa 269 fur seal Antarctic 403 New Zealand 123 northern 403 South American 403 Furbelows 148 Furneaux Group 480 Futuna, Île 473, 476 Fyn 433

G gabbro 42 Gabès, Golfo de 438 Gadus morhua 348 gafftopsail sea catfish 345 Gaidropsaurus mediterraneus 349 Gakkel Ridge 424, 425 Galapagos Fracture Zone 423, 457, 476 Galapagos Islands 92, 423, 457, 478 hot spot 478 influence of Peruvian Current 66, 478 lava flow 21 marine iguana 376, 478 Galapagos penguin 218, 478 Galapagos Rise 457, 479 Galeocerdo cuvier 332 Galicia Bank 437 Gallego Rise 457

Galway Bay 432 Gambia Estuary 120 Gambia Plain 429 Gambier Islands 477 Ganges delta 134, 177, 452–453 Ganges Fan 422, 447, 450 Ganges, Mouths of the 450 gannet, northern 378, 380, 391 gar, Cuban 133 garden eel, spotted 343 Gardner Pinnacles 468 Garofalo Whirlpool 82 gas deposits Bass Strait 112, 480 East China Sea 464 sedimentary basins 45 South China Sea 465 gas, in seawater 33 Gascoyne Plain 447, 451 Gascoyne Seamount 481 Gaspé, Péninsule de 431 Gasterosteus aculeatus 357 gastropods 279 anatomy 276 feeding 278 movement 277 Gastrotrich 316 Gavia immer 386 Gazelle Basin 481 Gazi Bay 149 Gecarcoidea natalis, migration 302, 303 geese 380 Geiranger Fiord 115 Gela Basin 438 gelatinous blindfish 183 gelatinous bryozoan 305 Gelidium foliaceum 244 Genoa, Gulf of 438 George Bligh Bank 430, 432 George V Coast 485 George VI Sound 484 Georges Bank 431 Georgia, Strait of 459 geotube 105 Gerupuk Bay 149 Gettysburg Seamount 437 Geyser Reef 454 gharial 134 ghost crab 301 Giacomini Seamount 459 giant anemone 266 giant brain coral 269 giant cladophora 247 giant clam 276, 281, 282–83 giant kelp 146–47, 151, 238, 240–41 destruction by purple sea urchin 310 sea otters 402 giant leaf worm 272 giant mussel shrimp 295 giant octopus 288 giant pyrosome 256, 319 giant sea spider 293 giant triton 285, 309 Giant’s Causeway 94–95 Gibbs Seamount 441 Gibraltar, Strait of 429, 437, 438 Gibson Seamount 459 Gigantocypris muelleri 295 Gilbert Ridge 467, 473 Gilbert Seamounts 457, 459 gills, fish 336 Gippsland Lakes 112 Giraud Seamount 454 Gironde Estuary 120 Gizhiginskaya Guba 461 glacials 46 glacial cycle 88 glaciation Alaskan mudflats 129 Chilean fiordlands 103 Puget Sound 102 Glacier Bay 459 glaciers 192, 194, 195 global warming, Peruvian Andes 91 glass squid 289

glasswort common 250, 251 The Wash 128 Glaucium flavum 252 Global Explorer ROV 172 global ocean conveyor 61, 62–63, 430 global warming Antarctic ice-shelf breakup 487 Arctic Ocean 65 Atlantic Conveyor 61, 62–63, 430 and sea-level change 88, 91, 487 global water cycle 64–65 Globicephala melas 418 Glossobalanus samiensis 314 Glottidia albida 315 Goban Spur 432, 437 goblin shark 329 goby Couch’s 148 yellow shrimp 364 Gofar Fracture Zone 478 Gold Coast 480 golden dune moss 249 Golden Gate channel 123 tide rip 82 golden jellyfish 10–11 Golfingia vulgaris 314 Gomera 436 Gonâve, Golfe de la 441 Gondwana 44, 45 breakup 482 climate change 46 Falkland Islands 445 Goniocorella dumosa 179 Goniopora djiboutiensis 268 Good Hope, Cape of 423, 482 Goodhope Bay 458 goose, brant 150, 381 goosefoot starfish 308 gooseneck barnacle 294 Gorda Plate 459 Gorgonia ventalina 265 gorgonin 265 Gorringe Ridge 437 Gotland 433 Gotland Basin 433 Goto-retto 464, 466 Gough Fracture Zone 423, 429, 482 Gould Coast 485 Graciosa 436 Graham Land 484 Grampus griseus 414 Grand Bahama Canyon 176 Grand Banks 431 Grand Banks of Newfoundland 429 Grand Cayman, “stingray city” 335 grand devil’s-claw 253 Grand Prix de Fécamp Yacht Race 57 Grande Comore 454 Grande, Bahía 444 granite 42 Seychelles 455 Grant Island 485 gravel beach 107 seabed 144 gravitation, Earth 40 gray heron 390 gray lichen 255 gray nurse shark see sand tiger shark gray reef shark 229 gray seal 404 Humber Estuary 119 gray-headed albatross 201 grease ice 198 gray whale 408 migration 417 Great Abaco 441 Great Abaco Canyon 441 Great Australian Bight 422, 447 Great Bahama Bank 156, 441 Great Bahama Canyon 441

Great Bahama Island 441 Great Barracuda 365 Great Barrier Reef 161, 162–63, 422, 456, 472, 473, 480 great black-backed gull 396 Great Blue Hole 157 great cormorant 393 great egret 125 Great Fisher Bank 433 great frigatebird 390 Great Ice Barrier 192 Great Inagua 441 Great Lakes 423 Great Meteor Tablemount 429, 436 Great Northern Diver 386 Great Salt Marsh, Cape Cod 126 Great Scallop 280 Great Shearwater 389 Great Skua 398 Great White Shark see White Shark Great Yangtze Bank 464, 466 Greater Antilles 423, 428, 440, 441 Greater Flamingo 132, 133 Greater Pipefish 146 Greater Weever 364 grebes 380 green algae 125, 248 Green Humphead Parrotfish 361 Green Paddle Worm 274 Green Sand Beach 470–471 Green Turtle 112, 158, 370 importance of seagrass 146 greenhouse gas 67 Greenland 423, 425 Greenland Coast 24–25 Greenland Fracture Zone 425, 427 Greenland Ice Coast 94 Greenland Ice Sheet 46, 430 global warming prediction 91 Greenland Plain 425, 427 Greenland Sea 423, 424, 425, 427 Greenland Shark 326 Greenland–Iceland Rise 341, 430 Grenada Basin 441 Grenadier, Pacific 349 Grey Islands 431 Grijalva Ridge 478 Grimpoteuthis plena 288 Gröll Seamount 442 Groote Eylandt 472 Ground Shark 323 grounding line 192 groundwater 64 Grouper, Potato 358 groynes 105 Gruinard Bay, post-glacial rebound 96 Guacanayabo, Golfo de 441 Guadalcanal 473 Guadalupe Seamount, biodiversity 211 Guadalupe, Isla 469 Guadeloupe Passage 441 Guafo Fracture Zone 457 Guaíba estuary 117 Guanay cormorant 380, 392 Guanghzou 122 guano 392 see also Jackass penguin Guantanamo Bay 441 Guatemala Basin 423, 457, 478 Guayaquil, Gulf of 478 Guérande salt marsh 128 Guevara Seamounts 445 Guiana Current 428, 442 Guinea Basin 423, 429, 443 Guinea Current 443 Guinea, Gulf of 429, 443 guitarfish, Atlantic 333 Gulf of Aden 448 Gulf of Alaska 459 Gulf of Aqaba, coral reef 158 Gulf of Bothnia 432 Gulf of California 469 Gulf of Corryvreckan 81

499

500

INDEX Gulf of Finland 432 Gulf of Guinea 443 tectonic triple junction 443 Gulf of Maine 431 Gulf of Mexico 116, 117, 440 Gulf of Odessa 439 Gulf of Oman 448 Gulf of St. Lawrence 116, 431 Gulf of Thailand 465 Gulf of Tongking 465 Gulf Stream 31, 66, 428, 431, 440 Atlantic Conveyor 63 map by Benjamin Franklin 59 gulfweed 235 gull great black-backed 396 herring 396 ivory 397 laughing 397 swallow-tailed 396 gulls 380 gully, erosion 176 gulper eel 343 gurnard, East Atlantic red 358 Gusinaya Bank 427 Guyot, Arnold Henry (1807–84) 174 guyots 174, 184 Gydanskiy Poluostrov 425 Gygis alba 397 Gymnodinium pulchellum 236 gypsum 32 gyres ocean 58 Arctic 424 Atlantic 428, 442 Comoros 455 Guatemala Basin 478 Gulf of Alaska 459 Indian Ocean 446 North Pacific 469 Pacific Ocean 456 South Pacific 477, 479 Southern Ocean 482, 483 upwelling and downwelling 60

H H2O molecule 30 Ha Long Bay, karst 102 hadal zone 168, 171, 219 Hadley cells 54 Haematopus ostralegus 394 hagfish 182, 318, 319 Japanese 319 Pacific 319 hairy angler 350 Haiyan, typhoon 72–73, 467 Haliaeetus leucogaster 393 Haliastur indus 393 halibut, Pacific 123 Halichoerus grypus 404 Halichondria panicea 259 Haliclona fascigera 259 Haliclystus auricula 262 Halimeda opuntia 247 Haliotis rufescens 284 halite 32 Halobacterium salinarium 233 Halobates 214, 292 Halobates sericeus 304 halocline 35 Halodule wrightii 148 halophiles 233 Halophilia ovalis 251 halophytes 249, 251 Halosphaera viridis 248 Hamelin Pool 150 hammerhead shark 322–23 scalloped 332 Hapalochlaena maculosa 288 Haplophryne mollis 351 harbor porpoise 418 harbor seal see common seal Hardanger Fiord 119 harlequin ghost pipefish 356 harlequin shrimp, molting 291

harlequin sweetlips 359 harp seal 404 harrier marsh 128 northern 126 Hastigerina pelagica 237 hatchetfish 224 lovely 347 Hatteras Island 95 Havelock Island 450 Hawaii lava coast 103 Hawaiian Archipelago 49, 161, 468 circulation 468 hawksbill turtle 158, 370, 372–73, 474 hazard from fishing 355 headlands, erosion 93 heat capacity 31 heat, internal, early Earth 40, 41 heating, solar 54, 66 Heinrich Events 195 Heliopora coerulea 160 Hellenic Trough 169, 439 hemocyanin 277 hemolymph 290 Hennediella heimii 249 Heptranchias perlo 325 Hercules ROV 173 hermaphrodites 279 Hermissenda crassicorni 286 Hermissenda sea slug 286 hermit crab 134 heron gray 390 madagascar 134 herons 380 herring gull 396 herring, Atlantic 344 herrings 339 Heterochone calyx 260 Heteroconger hassi 343 Heterodontus portusjacksoni 327 Hexabranchus sanguineus 287 Hexanchus griseus 325 highfin lizardfish 177 Hikurangi Trench 480 Himantopus himantopus 394 Himantura uarnak 333 Hippocampus bargibanti 357 Hippocampus hippocampus 356 Hirondella gigas 183 Histrio histrio 351 HMS Challenger 171 Hokkaido 460 Holacanthus ciliaris 359 holoplankton 214 Holothuria edulis 312 Homarus gammarus 297 Homotrema rubrum 108 honeycomb worm 275 Hong Kong Harbor 99 Honshu 460, 462–463 Hoorn Island 444 Hoplostethus atlanticus 353 hormogonia 233 Hormosira banksii 239 horn shark 323 horned-poppy, yellow 252 hornwrack 305 horseshoe crab 290 American 293 horseshoe worm 313, 314 hotspots 49, 174, 184 Azores Plateau 437 Cobb 459 Galapagos Islands 478 Hawaii 161, 468 Kerguelen 451 Marquesas Islands 477 Marshall Islands 467 Pacific Ocean 456, 468 Réunion 49, 455 hound needlefish 352 Huang He see Yellow River Humber Estuary 119 Humboldt Current 376, 456, 457, 478, 479 see also Peruvian Current Humboldt squid 277

hummingbird, bee 133 hump coral 268 humpback angler see common blackdevil humpback whale 408, 410–11, 416 feeding 200–201 migration 417 song 37, 409 humphead parrotfish 160 green 361 Hunter Ridge 473 Huon Peninsula New Guinea 472 tectonic uplift 102 hurricanes 70–71 Andrew 1992 133 coastal effects 71 development and structure 70 Frances 2004 71 Lili 2002 440 Rita 2005 73 Huso huso 340 Hutia, Cuban 133 Hybrid Remotely Operated Vehicle (HROV) 173 hydrocarbons cold seeps 189 as food source 179, 189 see also gas deposits; oil deposits hydrogen atoms 30 hydrogen bonds 30–31 hydrogen sulfide, hydrothermal vents 188 hydroid, stinging 262 Hydrolagus colliei 324 hydrologic cycle 64–65 hydrothermal vent crab 189 hydrothermal vents 32, 185, 188–189 archaea 232 East Pacific Rise 478 fauna 189 Pompeii worm 171 hydrozoans 261 Hydrurga leptonyx 405 Hyperoodon ampullatus 413 hyphae 254

I Iapetus Ocean 44 Iberian Plain 423, 429, 437 Ibiza 438 ice density 31 fast 198 first-year 198 frazil 198 grease 198 multi-year 198 pack 198 pancake 198 ice ages last 46–45 and sea-level change 46, 88–89 Big Sur 103 Gruinard Bay 96 ice breakers 199, 424, 485 Ice Coast, Greenland 94 ice lead 199 ice platelets 198 ice rafting 195, 198 ice see sea-ice ice shelves Antarctic 192–93, 484, 485 breakup 487 satellite monitoring 187, 487 ice-sheets 64, 88 Antarctic 46, 482 icebergs 194–95, 424 B-15 485 calving 192, 195 detection 195 Labrador Current 431 satellite monitoring 187 Southern Ocean 482

icefish, blackfin 361 Iceland 423, 425 Iceland Basin 423, 429, 430, 432 Iceland Plateau 425, 427, 430 ichthyosaur 228 icon star 308 Iconaster longimanus 308 Idiacanthus antrostomus 347 igneous rocks 42 iguana, marine 368, 376, 478 Imarssuak Channel 429 imitating flatworm 272 impact crater, Chesapeake Bay 116 Inca tern 397 Indian Ocean 446–47, 451, 454–55 circulation 446, 447, 451 depth 169 ocean floor 446 winds 447 Indian Plate 423, 446, 448, 450, 455 Indo-European humpback dolphin 414 Indo-Pacific crocodile see saltwater crocodile Indomed Fracture Zone 446 Indonesian coelacanth 340 Indus Fan 447, 449 Indus River 448 infantfish, snout 161 ink, octopus defense mechanism 288 Inland Sea 83, 464, 466 Inner Hebrides 432 Inner Islands 454 insects 292 inshore hagfish see Japanese hagfish Institut Okeanologii Rise 461 Integrated Ocean Drilling Program 41 interference, wave 76 interglacials 46 internal waves 76 intertidal habitat 78 intertidal rove beetle 304 inverse estuaries 122 invertebrates 256 Investigator Ridge 422, 447, 451 Invisible Bank 450 Iodictyum phoneniceum 305 Ionian Basin 439 Ionian Islands 439 Ionian Sea 438, 439 ions, in seawater 32 Ipomoea imperati 252 Ireland 423 Ireland Trough 432 Irish moss 245 Irish Sea 432 iron banded-iron formation 43 Earth’s core 41 in seawater 33 iron catastrophe 40 Irrawaddy dolphin 135 Irrawaddy, Mouths of the 450 irrigation, Murray River 121 Isakov Seamount 466 Iselin Bank 485 Iselin Seamount 485 Ishigaki Island 160 Isistius brasiliensis 326 island arc formation 48, 464, 467, 468 island chains 49, 456, 477, 480 Islas Orcadas Ridge 482 Islas Orcadas Rise 429, 445 Istiophorus albicans 365 ivory gull 397 Iwo–Jima Ridge 464, 466, 467 Izembek Lagoon 150 Izu Spur 464, 466 Izu Trench 464, 466 Izu-shoto 464, 466

J jabiru stork 131, 132 jackass penguin 383 jaeger, parasitic 398 Jaguar Seamount 454 Jamaica Channel 441 James Island, Gambia Estuary 120 James Ross Island 484 Jan Mayen 425, 427 Jan Mayen Current 427 Jan Mayen Fracture Zone 425, 427 Jan Mayen Island 427 Jan Mayen Ridge 425 Japan Basin 456, 460, 461 Japan Trench 422, 456, 460, 461, 464 Japan, Sea of 422 Japan, Sea of/East Sea 456, 464, 466 Japanese hagfish 319 Japanese spider crab 297 japweed 239 Jarvis Island 476 Jason Peninsula 484 Jason-2 satellite 187 Java 422, 447, 451, 456 Java Ridge 447. 451 Java Sea 422, 451, 456 Java Trench 169, 183, 422, 446, 447, 451 Jaza’ir Farasan 448 Jazirah 465 Jazirah Doberai 466, 472 Jeffreys Bay 110 jelly weed, small 244 jellyfish box 261, 264 common, larva 214 deep-sea 262 golden 10–11 moon 262 stalked 262 upside-down 264 jellyfish 260–61 jewel anemone 143, 267 jewelry, coral 260 Jodies Basin 485 John Dory 353 Johnson Sea-Link submersible 173 Johnston Atoll 468 Joinville Island 444, 484 Jones Sound 426 Joseph Bonaparte Gulf 472 Juan de Fuca Plate 423, 459 Juan de Fuca, Strait of 459 Juan Fernández, Islas 479 Juby, Cap 437 Junceella fragilis 265 Jurassic ocean life 228 plate tectonics 45 Jutland Bank 432, 433 Jutland, sand dunes 109 Juventud, Isla de la 441 Jylland 433

K Kaburakia excelsa 272 Kachchh, Gulf of 449 Kai, Kepulauan 472 Kamchatka Basin 458, 461 Kamchatka Peninsula 422, 456, 458, 460, 461 Kamchatka Terrace 458 Kamchatskiy Zaliv 458, 461 Kammu Seamount 457, 468 Kanton 476 Kap Hoorn see Cape Horn Kara Sea 422, 425, 427 Kara Strait 425, 427 Karaginskiy Zaliv 458, 461 Karaginskiy, Ostrov 458 Karkinitt, Gulf of 439 Karpathos 439

INDEX karst Ha Long Bay 102 Krabi Coast 99 Kashevarov Bank 461 katabatic wind 193 Kathetostoma laeve 364 Kathiawar Peninsula 449 Kattegat 432, 433 Kaua‘i 468 Kavachi volcano 472 Kazan-retto 464, 466 keel-billed toucan 132 keelworm 143 Kellett, Cape 424, 426 kelps 234 kelp Asian 150 bull 150, 151 giant 146–47, 151, 238, 240– 41 destruction by purple sea urchin 310 sea otters 402 split-fan 148 sugar 148 kelp anemone 147 kelp fly 290, 304 kelp forests 146–47, 148 kelp limpet 148 kemp Ridley turtle see Atlantic Ridley Turtle Kenai Peninsula 459 Kerala backwaters 121 Kerch Strait 439 Kerguelen 447, 483 Kerguelen Hotspot 451 Kerguelen Plateau 422, 447, 482, 483 Kermadec Islands 476, 481 Kermadec Ridge 481 Kermadec Trench 422, 457, 476, 481 Kermadec–Tonga Trench 480 keys see cays Khambhat, Gulf of 449 Khayyam Seamount 469, 478 Kiel Bay 433 Kiel Canal 432 Kikori River 135 Kilauea, volcano 38–39, 103, 468 killer whale 415 Kinabatangan Mangroves 135 King Island 480 king penguin 382 King Peninsula 484 king ragworm 275 king scallop see great scallop King William Island 424, 426 kingfisher collared 399 pied 399 red-breasted paradise 135 kingfishers 380 Kingman Reef 476 Kings Trough 436, 437 kinorhynchs 313 Kiritimati 476 Kiska Island 458 kite, Brahminy 393 kittiwake, black-legged 397 Kitty Hawk Seamount 465 Klaipeda Strait 119 Knipovich Ridge 425, 427 Knipovich Seamount 442 knotted wrack 239 Knowles, Cape 484 Knox, Cape 459 Ko Samui 465 Kodiak Island 457, 459 Kodiak Seamounts 459 Kolbeinsey Ridge 425, 430 Komandorskiye Ostrova 458, 461 Komoë River 121 Korea Bay 464 Korea Strait 460, 464, 466 Korean Plateau 460, 464 Korff Ice Rise 484 Koro Sea 473, 476, 481 Kosrae 467 Kotzebue Sound 424

Kowloon Peninsula 99 Kra, Isthmus of 465 Krabi Coast 99 krait, sea, yellow-lipped 368, 374 krill Antarctic 199, 291, 295 and water temperature 291 Kronotskiy Zaliv 458, 461 Kronprinsesse Martha Kyst 484 Kure Atoll 468 Kuril Gap 461 Kurile Basin 456, 461 Kurile Harbor seal 460 Kurile Islands 422, 456, 460, 461 Kurile Trench 422, 456, 458, 460, 461 Kuroshio Current 58, 59, 66, 456, 457, 459, 460, 464, 467 Kuroshio Extension 456, 459 Kuskokwim Bay 458 Kvitøya 425, 427 Kwajalein Atoll 161, 467 Kyushu 456, 460, 464, 466 Kyushu-Palau Ridge 456, 464, 465, 466, 467

L L’Haridon Bight 111 La Nao, Cabo de 438 La Niña 69 La Palma 436 La Palma, Canary Islands 437 La Pérouse Seamount 454 La Perouse Strait 461 La Plata dolphin 118 Labrador Basin 423, 429 Labrador Current 59, 116, 195, 426, 431 Labrador Sea 423, 429 Labroides dimidiatus 361 Labrus mixtus 361 labyrinthulids 254 Labyrinthuloides species 254 Laccadive Islands 447, 448, 449, 455 ladyfish 341 Laeso 433 Laetmogone violacea 312 Lagoa dos Patos 117 lagoons coastal 115 coral reef 152, 154 Laguna de Términos 148 Laguna Madre 117 Laguna San Ignacio 123 Laizhou Wan 464 Lake Alexandrina 121 Lake Okeechobee 132 Laminaria hyperborea 148 Laminaria ochroleuca 148 Laminaria pallida 148 Laminaria saccharina 148 Laminariales 146, 238 lamp shell 315 lampern 319 Lampetra fluviatilis 319 lamprey 318 Humber Estuary 119 river see lampern sea 319 Lampris guttatus 348 Lana‘i 468 Lancaster Sound 426 Lancaster Trough 426 lancelet 319 anatomy 318 land uplift, and sea-level change 88–89 Land’s End 432, 437 Landlady’s Wig 238 Langebaan Lagoon 148 Langmuir circulation cells 61 lanternfish 233 spotted 347 lanternshark, velvet belly 326 Lanzarote 437

Laptev Sea 422, 425 Larosterna inca 397 Larsen Ice Shelf 192, 193, 486, 487 Larsen Ice Shelf 484 Larsen Sound 424, 426 Larus argentatus 396 Larus atricilla 397 Larus marinus 396 Lasaea rubra, in black tufted lichen 255 Lassiter Coast 484 Latady Island 484 lateral-line 323, 336 Laticauda colubrina 374 Latimeria chalumnae 340 Latimeria menadoensis 340 Lau Basin 473, 476, 481 Lau Group 473, 476, 481 Lau Ridge 473, 476, 480, 481 laughing gull 397 Laurasia 45 Laurentia 44 Laurentian Fan 431 Laurentian Trough 431 Laurentide Ice Sheet 46, 431 lava basaltic 38–39, 42 sand 112 pillow 185, 456 lava flow Galapagos Islands 21 Hawaii 38–39, 103 Laver 245 laverbread 245 Lavoisier Island 484 Laysan Island 468 Lazarev Sea 429, 482 Leach’s storm petrel 389 leaf-scaled sea snake 375 leafy seadragon 356 least auklet 399 least tern 126 leatherback turtle 113, 371 migration 220 Leeward Islands 441 lemon shark 323 lemon sponge 259 Lena River, discharge into Arctic Ocean 200, 424 Lena Seamount 446 Lena Trough 425, 427 leopard seal 405 Lepadogaster lepadogaster 352 Lepidochelys kempi 371 Leptonychotes weddell 405 Les Pitons, St. Lucia 95 Lesbos 439 Lesser Antilles 440, 441 volcanic arc 95 Lesser Sunda Islands 451, 472 Lessonia variegata 150 Leucetta species 259 Levantine Basin 439 levees, New Orleans 73 Leven Bank 454 Lexington Seamount 465 Leyte 465, 466 Liaodong 464 lichen 254 black tar 255 black tufted 255 gray 255 yellow splash 255 Lichina confinis 233 Lichina pygmae 255 life ocean, history 226–229 origin 226 Ligeti Ridge 445, 484 light-mantled sooty albatross 386 light, wavelength 36–37 Lighthouse Reef 156–57 Ligia oceanica 295 Ligurian Sea 438 Liman Current 150 limestone Amalfi Coast 97 chemical erosion see karst limey petticoat 238 Limonium vulgare 252

limpet blue-rayed 147, 148 common 284 kelp 148 slipper, sex change 279 Limos 439 limpets, feeding 278 Limpopo River 158 Limulus polyphemus 293 Lincoln Sea 425 Lindesnes 433 Line Islands 457, 476 lined chiton 289 Lineus longissimus 273 Lingga, Kepulauan 451, 465 linguid brachiopod 315 Linnaean hierarchy 206 Linnaeus, Carolus (1707–78) 206 lionfish 357 Red Sea 158, 210 Lisburne, Cape 424 Lisianski Island 468 lithosphere 42 Litke Trough 425, 427 Little America Basin 485 Little Bahama Bank 156, 441 little egret 390 little penguin 383 Littorina littorea 285 live sharksucker 360 lizard, water monitor 134 lizardfish highfin 177 reef 347 lizards 368–69 lobe-finned fish 227 see also coelacanth Lobodon carcinophagus 405 lobster Caribbean spiny, migration 220 common 297 Norway 145 packhorse 15 spiny 297 squat 143, 175, 178, 179 violet-spotted reef 230–31 Loch Carron, biodiversity 211 Lofoten Maelstrom 80 loggerhead turtle 370 Loligo vulgaris 289 Lolland 433 Lombok Basin 451 Lombok, seagrass 149 Lomonosov Ridge 425 Lomonsov Ridge 424 London Reefs 465 Londonderry, Cape 451, 472 Long Bay 441 Long Island 431, 441 long-finned pilot whale 418 long-legged spider crab 300 long-snouted spinner dolphin 414 long-spined bullhead 357 long-spined sea urchin 310 longfin bannerfish 160, 161 longnose sawshark 326 longshore drift 93, 106 Lontra felina 402 Lookout, Cape 431 loon, common 386 loons (sea birds) 378–379, 380, 391 Lopez, Cap 443 lophelia coral 178, 179, 269 Lophelia pertusa 153, 178, 179, 269 Lophius piscatorius 351 Lord Howe Island 480, 481 Lord Howe Rise 422, 456, 481 Lord Howe Seamounts 481 Los Roques Basin 441 Los Roques, Islas 441 Lost Dutchmen Ridge 451 Loubet Coast 484 Lougheed Island 424, 426 Louisiade Archipelago 472, 473 Louisiade Plateau 473 Louisville Ridge 422, 457, 476, 480, 481

lovely hatchetfish 347 Low Country, South Carolina 127 Loyalty Islands 473, 481 luciferin 224 lugworm 125, 274, 313 Luidia ciliaris 308 Luitpold 484 lumpsucker 147, 358 lures, bioluminescent 225 Lutjanus kasmira 359 Lutra lutra 402 Luzon 465, 466 Luzon Ridge 465, 466 Lyddan Island 484 Lyra Basin 466 Lyra Reef 466, 473

M Mabahiss Fracture Zone 455 macaque, rhesus 134 macaroni penguin 383 Macclesfield Bank 465 Mackenzie Bay 422, 483 Mackenzie King Island 424, 426 Mackenzie River delta, discharge into Arctic Ocean 63 mackerel shark 323 mackerel, Atlantic 365 Macquarie Island 481 Macquarie Ridge 456, 480, 481 Macrocheira kaempferi 297 Macrocystis pyrifera 238, 310 Macronectes giganteus 388 Macropodia rostrata 300 Madagascar 422, 446, 455 mangroves 134 Madagascar Basin 422, 446, 454 Madagascar fish-eagle 134 Madagascar heron 134 Madagascar Plateau 422, 446, 454 Madagascar teal 134 Madeira 436 Madeira Plain 423, 429, 436 Madeira Ridge 436 Madeleine, Îles de la 431 Madingley Rise 454 Madrakah, Ra’s 449 Madrepora oculata 179 maelstrom 80 maerl 144, 148, 245 Maewo 473 Mafia 454 Magellan Rise 476 Magellan Seamounts 456, 466 Magellan, Ferdinand (c.1480– 1521) 444, 456, 477 Magellan, Strait of 444 Magellanic flightless steamer duck 381 Magellanic penguin 383 magma 42, 185 magnesium, in seawater 32 magnetite, in cetacean brains 417 magnificent feather duster 275 Mahabiss Fracture Zone 447 Mahana Beach see Green Sand Beach, Papakolea Beach Maine, Gulf of 431 Majorca 438 Majuro Atoll 161, 467 Makarov Basin 424, 425 Makarov Seamount 456, 466 Makassar Strait 451, 456, 465, 472 Makran Coast 449 Malacca, Strait of 447, 450, 465 Malacosteus niger 347 Malaita 473 Malay Peninsula 447, 465 Malden Island 476 Maldives 159, 447, 448, 455 Maldives anemonefish 218 Malekula 473 Malin Head 432 Mallorca Channel 438 Mallotus villosus 345

501

502

INDEX Malta Channel 438 Malta Plateau 438 Malta Trough 438 Malvinas current 59 mammals 400–401 anatomy and physiology 400 breeding 400 classification 209, 401 conservation 400 exploitation 400 feeding 400 Man, Isle of 432 managed retreat 105 manatee Antillean 132, 401 Florida 133 importance of seagrass 146 West African 418 West Indian 419 mandarin fish 337, 364 Mangaia 476 manganese nodule 182 mangrove black 130, 132, 135 button 130 red 130, 132 white 130, 132 mangrove brittlestar 131 mangrove jack 135 mangrove kingfisher see collared kingfisher mangrove monitor 377 mangrove swamps 130–131 biodiversity 131 formation 130 plants 130 mangroves aerial roots 135 Gazi Bay 149 Madagascar 134 New Guinea 136–37 as tsunami protection 134 Manihiki Plateau 457, 476, 477 Manila Trench 465 Manjuari 133 Mannar, Gulf of 450 Mansel Island 426 Manson Bank 485 Manta birostris 335 manta ray 158, 160, 335 mantle Earth 41 convection cells 41, 42, 44 sampling 41 Manus Island 466, 472 Manus Trench 466, 472 Mapmaker Seamounts 422, 456, 467 Maracá, Ilha de 442 Maracaibo, Lake 441 Marajo Island 118 Marajó, Ilha de 442 Maranhao Seamount 442 Marcet, Alexander (1770–1822) 32 Marcus Island 466 Margarita, Isla de 441 Marguerite Bay 484 Mariana Islands 467 Mariana Ridge 466 Mariana Trench 169, 171, 183, 422, 456, 466, 467 Marie Byrd Land 485 Marie Celeste Fracture Zone 447, 455 marine otter 402 marine skater 292, 304 marine terraces 89, 103 marine-deposition coasts 93 Marmara, Sea of 439 Marquesas Fracture Zone 423, 457, 477 Marquesas Islands 423, 457, 477 marram grass 107, 109, 113, 243, 251 marsh elder 127 marsh harrier 128 marsh periwinkle 127 marsh samphire see common glasswort

marsh wren 127 Marshall Islands 161, 467 Marshall Seamounts 457, 467 marshes, as tidal barrier 105 Marsili Seamount 438 Martaban, Gulf of 450 Martha’s Vineyard 431 Martin Peninsula 484 Martin Vaz, Ilhas 442 Martinique Passage 441 Mascarene Basin 422, 446, 454, 455 Mascarene Islands 454 Mascarene Plain 446, 454, 455 Mascarene Plateau 422, 446, 454, 455 Mascaret tidal bore 120 Masirah, Jazirat 449 Masirah, Khalij 449 Masoala, Tanjona 454 mass extinction 228, 229 Mastigias 10–11 Mastocarpus stellatus 245 Matagorda Bay 115 Mathematicians Seamounts 457, 469 Maud Rise 429 Maui 468 Mauna Loa volcano 112, 468 Maupihaa, Society Islands 161 Maupiti, Society Islands 161 Mauritius 446, 455 Mauritius Trench 454 mauve stinger 225, 263 Mawsonite 226 Maxwell Fracture Zone 436 Mayan Cichlid 133 Mayotte 454 McClintock Channel 424, 426 McClure Strait 424, 426 Mecklenburg Bay 433 Medina Bank 438 Mediterranean Basin, history 45 Mediterranean bath sponge 259 Mediterranean monk seal 404 Mediterranean red coral 266 jewelry 260 Mediterranean Ridge 439 Mediterranean Sea 422, 423, 429, 437, 438–39 depth 169 evolution 45 Mednyy Seamount 458, 461 Mednyy, Ostrov 458 medusae 260–61 Megachasma pelagios 328 Megalops atlanticus 341 Megamouth Shark 328 Megaptera novaeangliae 408 Meghna delta 134 meiofauna 313 Melanesia 422, 456, 472–73 Melanesian Basin 422, 456, 467 Melanocetus johnsonii 351 Melita Bank 438 Mellish Rise 473, 480 Mellish Seamount 468 melting point, water 31 melting, impact, early Earth 40 Melville Island 424, 426, 472 Melville Peninsula 424, 426 Melville Trough 424, 426 Menard Fracture Zone 423, 457, 483 Mendaña Fracture Zone 423, 457, 479 Mendeleyev Plain 424 Mendeleyev Ridge 422, 424 Mendocino Fracture Zone 423, 457, 468, 469 Mendoza Rise 479 Mentawai Basin 451 Mentawai Ridge 451 Mentawai Trough 451 Mentawai, Kepulauan 451 merganser, red-breasted 381 Mergui Terrace 450 Mergus serrator 381 meristem 233 mermaid’s wineglass 247

meroplankton 170, 214 Mesozoic climate 46 giant marine reptiles 228 Messina, Strait of 438 Meta Incognita Peninsula 426 metamorphic rock 42 meteorite impact crater, Chesapeake Bay 116 Meteosat satellite 187 methane cold seeps 189 as food source 179 methane-fixing bacteria 189 METOP-A 54 Metridium senile 267 Mexico Basin 440 Mexico, Gulf of 423, 428, 440 Michelson Ridge 466 microalgae 248 Micronesia 422, 456, 466, 467 Mid-Atlantic Ridge 184, 185, 423, 424, 428, 429, 430, 436, 437, 442, 443, 482 Mid-Indian Basin 422, 447, 451, 455 Mid-Indian Ridge 422, 446, 447, 455 Mid-Ocean Canyon 429, 436 Mid-Ocean Channel 423 mid-ocean ridges 42, 174, 182, 185 creation of oceanic crust 48 and sea-level change 88 Mid-Pacific Mountains 422, 456 Mid-Pacific Seamounts 467, 468 Middle America Trench 423, 457, 469, 478 Midway Islands 161, 457, 468 migration 220–21 birds 380 red crab 302, 303 tracking 220 vertical 221 wedge-tailed shearwater 389 whales 417 milkfish 339, 344 Millennium Island 476 Miller Seamount 459 milletseed butterflyfish 161 Milne Seamounts 436 Minack Theatre 109 Minami Daito Basin 464 Minas Basin 126 Minch, The 432 Mindanao 465, 466 Mindoro 465, 466 minerals hydrothermal vents 188 in seawater 32 Minicoy Island 449 minke whale 409 Minorca 438 Mirim Lagoon 117 Mirounga angustirostris 405 Mirtoo Pelagos 439 Mississippi Estuary 116 Mississippi Fan 440 Mississippi Slope 440 Mississippi-Alabama Shelf 440 Mitsukurina owstoni 329 mixed estuary 114 Mnemiopsis leidyi 317 moai, Easter Island 479 Moeraki Beach 112 Mohéli 454 Mohns Ridge 425 Mohorovicic discontinuity (Moho) 42 Mola mola 367 molecules, water 30–31 mollusks 276–79 anatomy 276 classification 208, 279 feeding 278 lifecycles 279 movement 277 reproduction 279 respiration 277 sense organs 277

Moloka‘i 468 Molokai Fracture Zone 423, 457, 468, 469 Molokini Island 49 molting, arthropods 291 Molucca Sea 451, 465, 466, 472 Moluccas 451, 456, 465, 466, 472 Mona Canyon 441 Mona Passage 441 Monachus monachus 404 Mondego, Cabo 437 monitor lizard mangrove 377 water 134, 377 monkey proboscis 135 rhesus macaque 134 spider 132 monkfish see angler Mono Rise 441 Monodon monocerus 413 monoplacophorans 279 monsoon, Indian 54, 446, 450, 473 Monterey Bay 469 kelp forest 151 Monterey Canyon 469 Monterey Fan 469 Montevideo 118 Moon formation 40 influence on tides 78–79 moon jellyfish 262 moon snail 217 moonfish see opah Moonless Mountains 457, 469 Moorea 476 Moorea, Society Islands 161 moray eel, chain 342 Moray Firth 432 Morecambe Bay 127 Morelet’s crocodile 132 morning-glory, beach 252 Mornington Abyssal Plain 423, 457, 483 Moro Gulf 465, 466 Moro Reef 468 Morotai, Pulau 465, 466 Morris Jesup, Kap 425 Morus bassanus 391 mosaic sea star 308 mosasaurs 228 Moskenstraumen see Lofoten Maelstrom Mosquito Bank 441 Mosquito Coast 441 moss golden dune 249 saltmarsh 249 seaside 249 Southern beach 249 mosses 249 Mouchoir Passage 441 Mount Desert Island 94 Mount St. Helens, volcanic eruption 184, 459 Mozambique Channel 422, 446, 454, 455 Mozambique Escarpment 446, 482 Mozambique Plateau 422, 446, 454 mud bioturbation 313 seabed 144 mud dragon 316 mud-shrimp, Bay of Fundy 126 mudflats 124 Alaskan 129 Guérande 128 Minas Basin 126 Morecambe Bay 127 Saemangeum Wetlands 129 The Wash 128 Wadden Sea 127 see also common glasswort mudskipper 135 Muelleriella crassifolia 249 Muertos Trough 441 multi-year ice 198

multihulls, ocean yacht racing 57 Munidopsis serricornis 178 Munk, Walter (born 1917) 37 Murex pecten 284 Murmansk Rise 427 Murray Fracture Zone 423, 457, 468, 469 Murray Ridge 447, 449 Murray River 121 Murray Seamount 459 murre, common 14, 378–79, 398 Mururoa 477 Musashi Banks 461 mushroom coral 269 mushroom leather coral 264 Musicians Seamounts 457, 468 Mussau Trench 466 mussel common 280 ribbed 127 mutualism 217, 292 Myctophum punctatum 347 Myrichthys colubrinus 343 Myripristis vittata 352 Mys Alevina 461 Mys Aniva 461 Mys Enkan 461 Mys Olyutorskiy 461 Mys Shipunskiy 461 Mys Sivuchiy 461 Mys Taygonos 461 Mys Terpeniya 461 Mys Tolstoy 461 Mys Yelizavety 461 Mys Yuzhnyy 461 Mytilus edulis 280 Myxine glutinosa 319

N Namibia Plain 429 Nankai Trough 464, 466 Nansen Basin 422, 425 Nansen Fracture Zone 424 Nansen, Fridjtof (1861–1930) 201 Nantucket Island 431 Nares Plain 423, 429, 441 Nares Strait 425, 426 Naruto Whirlpool 83 narwhal 413 Nashville Seamount 441 Naso vlamingii 364 Nassau 476 Natal Basin 422, 446, 454, 455 Natator depressus 371 National Oceanic and Atmospheric Administration, hurricane monitoring 70 natterjack toad 125 Natuna Sea 451, 465 Natuna, Kepulauan 465 Naturaliste Fracture Zone 447 Naturaliste Plateau 447 Naucrates ductor 360 nautilus (cephalopod) 33, 288 Nautilus pompilius 288 Nautilus, (US submarine) 199 Navarin, Mys 458 Navarino, Isla 444 navigation animal 221 whales 417 Nazareth Bank 454 Nazca Plate 478, 479 Nazca Ridge 423, 457, 479 Neanthes virens 275 neap tides 79 Near Islands 458 nearshore 106 Nebrius ferrugineus 327 Necker Island 468 Necker Ridge 468 needle rush 127 needlefish, hound 352 Needles Overfalls 82 Negros 465, 466

INDEX nekton 165, 214 sunlit zone 170 Neman River, discharge 119 nematodes 313 Nemaya Zemyla 422 nemertean worms 273 Nemichthys scolopaceus 342 Neoceratium tripos 236 Neocrinus decorus 311 Neogene, ocean life 228 neptune grass 251 Neptune’s necklace 239 Nereocystis luetkeana 150 neuston 168 Nevel’skoye Seamount 461 New Britain 472 Trench 472 New Britain Trench 472 New Caledonia 456 New Caledonia Basin 480, 481 New Caledonia Trough 473, 481 New England Seamounts 429 New Georgia Islands 473 New Georgia Sound 473 New Guinea 422, 456, 465, 466, 472 New Guinea flightless rail 135 New Guinea mangroves 135 New Guinea Trench 466, 472 New Hebrides Ridge 481 New Hebrides Trench 457, 473, 481 New Ireland 466, 472 New Zealand 422, 457, 480, 483 New Zealand fur seal 123 Newenham, Cape 458 Newfoundland 423, 431 Newfoundland Basin 423, 429, 436 Newfoundland Seamounts 436 Newman Island 485 Nias, Pulau 451 Nicaraguan Rise 441 nickel, Earth’s core 41 Nicobar Islands 159, 447 nictating membrane, sharks 323 Niger delta 443 Niger Fan 429, 443 Nihoa 468 Nile crocodile 134 Nile Delta, deposition 97 Nile Fan 439 Ninety Mile Beach 111, 112 Ninetyeast Ridge 422, 446, 447, 450, 451 Ningaloo Reef, whale sharks 328 Nipponnemertes pulcher 273 nitrates, in seawater 33 nitrogen early Earth 43 in seawater 33 nitrogen-fixing bacteria 233, 243 Nitrosomonas 232 Noctiluca scintillans 236 green algae 248 noddy, brown 397 nodose box crab 297 nodule, manganese 182 Nordaustlandet 425, 427 Norfolk Island 481 Norfolk Ridge 457, 481 nori 245 North American Plate 423, 437, 458 North Atlantic Drift 59, 66, 427, 428, 430, 431, 432 Atlantic Conveyor 63 North Australian Basin 447, 451 North Cape 425, 427 North Channel 432 North Equatorial Current 428, 440, 446, 447, 456 North Fiji Basin 422, 457, 473, 481 North Island 457, 481, 483 North Jutland Dunes 109 North Kanin Bank 427 North Kenya Bank 454 North Makassar Basin 451, 465

North New Hebrides Trench 473 North Oki Bank 461, 464 North Pole 424, 425 North Sea 119, 423, 429, 432, 433 depth 169 Northwest Cape 451 Northwest Passage 426 North, Cape 431 northern bluefin tuna 365 northern bottlenose whale 413 Northern Cook Islands 457, 476 northern fulmar 388 northern fur seal 403 northern gannet 378, 380, 391 northern harrier 126 northern Mariana Islands 467 northern right whale 408 Northern Spencer Gulf Estuary 122 Northland Plateau 481 Northwest Georgia Rise 445 Northwest Hawaiian Ridge 468 Northwest Pacific Basin 422, 456, 458, 460, 461, 466 Northwest Slope 440 Northwind Plain 424 Northwind Ridge 424 Norton Plain 458 Norton Sound 458 Norvegia, Cape 482, 484 Norwegian Atlantic Current 425, 432 Norwegian Basin 423, 425, 427, 429, 433 Norwegian Sea 423, 425, 427, 429, 430, 432, 433 tidal races 80–81 Norwegian Trench 425, 432, 433 Nosy Be 454 Nosy Glorieuses 454 Nosy Sainte Marie 454 notch, wave-cut 93 Noto-hanto 461 notosaurs 228 Notre Dame Bay 431 Nottingham Island 426 nourishment, beach 105 Nova Scotia 431 Nova Trough 457, 476 Novaya Zemlya 425, 427 Novosibirskiye Ostrova 422, 425 Nucella lapillus 284 nudibranchs see sea slugs Nuku Hiva 477 Nukunonu Atoll 476 Numenius phaeopus 395 Nunivak Island 458 nurseries, kelp forests and seagrass beds 147 Nusa Tenggara 160 Nutibara Trough 441 nutrients cycle 212 in seawater 33 Nyasa, Lake 454

O O‘ahu 468 O‘Gorman Fracture Zone 478 O2, in seawater 32, 33 Oarfish 348 Oates Bank 485 Ob’ Trench 447 Obelia, bioluminescence 224 Obruchev Rise 458, 461 Obruchev Seamount 461 Obskaya Guba 425 ocean circulation, polar 200–201 ocean deserts 219 ocean floor plate tectonics 48–49 structure 42

ocean gyres 58 ocean sunfish 215, 367 ocean temperature satellite monitoring 187 and sea-level 88 ocean trenches 183 ocean warming 192 ocean winds 54–55 ocean yacht racing 56–57 ocean-air interface 168, 214 oceanic crust 42 recycling 48 Oceanites oceanicus 389 Oceanodroma leucorhoa 389 Oceanographer Fracture Zone 423, 429, 436 oceanography, satellite 186–87 oceans acidification 67 depth, average 169 depth, satellite estimates 187 evolution 44–45 life, history 226–29 origin 42–43 world 422–23 zones depth 168–71, 219 geographical 218 life 218–19 ocelli 277 Octocoral 175 octopus blue-ringed 288 dumbo 288 giant 288 Ocypode saratan 301 Odden ice tongue 427 Odobenus rosmarus 403 Odontodactylus scyllarus 295 Oeno Island 477 offshore breezes 55 Ogasawara Trough 464, 466 Ogasawara-shoto 464, 466 Ogcocephalus radiutus 350 Oikopleura labradoriensis 319 oil deposits Atlantic Ocean 428 Beaufort Sea 426 continental slope, UN Convention on the Law of the Sea 177 evaporite traps 141 Gulf of Guinea 443 Gulf of Mexico 428, 440 Niger Delta 443 North Sea 428, 432 Persian Gulf 448 Sakhalin Island 460 Sea of Okhotsk 460 sedimentary basins 45 South China Sea 465 Timor Sea 451 Oithona similis 294 Okhotsk Plate 423, 460 Okhotsk, Sea of 422, 456, 458 Oki Bank 461 Oki Ridge 461, 464 Oki Trough 461, 464 Oki-shoto 461, 464 Okidaito Ridge 464, 465, 466 Okinawa 464, 466 Okinawa Trough 464, 466 Öland 433 Old Harry Rocks 93 Old Sow Whirlpool 80 Oléron, Île d’ 437 olive sea snake 375 Olympus Knoll 436 Olyutorskiy Zaliv 458, 461 Olyutorskiy, Mys 458 Oman Basin 449 Oman, Gulf of 446, 449 Ona Basin 444 Oncorhynchus kisutch 346 onshore breezes 55 Onslow Bay 441 Ontong Java Rise 456, 466, 472, 473

ooze biogenic 180, 181 calcareous 180, 181 deep sea 223 siliceous 181 opah 348 Oparin, Aleksandr I. (1894–1980) 226 Ophiothrix fragilis 309 Opisthoproctus soleatus 345 Opsanus tau 349 orange fairy basslet 162–63 orange fiddler crab 301 orange river 443 orange roughy 175, 353 orange sea pen 266 orange, cabo 442 Orchestia gammarellus 295 Orcinus orca 415 Oregon National Dunes 113 Oresund Bridge 432 organ pipe coral 264 Orkney Deep 445, 484 Orkney Islands 432 Orona 476 Orozco Fracture Zone 469, 478 Ortegal, Cabo 437 Orville Coast 484 Osborn Plateau 447, 451 Oscillatoria willei 233 osculum 260 Oshawa Seamount 459 Osmerus eperlanus 345 Osmia aurulenta 304 Osprey 393 Ostracion meleagris 366 Ostrov Belyy 425 Ostrov Beringa 461 Ostrov Bol’shevik 425 Ostrov Bol’shoy Lyakhovskiy 425 Ostrov Iturup 461 Ostrov Karaginskiy 461 Ostrov Kolguyev 427 Ostrov Komsomolets 425 Ostrov Kotel’nyy 425 Ostrov Kunashir 461 Ostrov Mednyy 461 Ostrov Novaya Sibir’ 424 Ostrov Oktyabr’skoy Revolyutsii 425 Ostrov Paramushir 461 Ostrov Sakhalin 422, 456, 461 Ostrov Simushir 461 Ostrov Urup 461 Ostrov Vrangelya 424 Ostrovnoy Seamount 461 Otranto, Strait of 439 otter European 402 marine 402 sea 151, 401, 402 Otway, Cape 480 Outer Bailey 430, 432 Outer Hebrides 430, 432 outwash fan 176 overfalls 79, 82 overfishing 348 cod 212 sand eel 399 Owen Fracture Zone 446, 448, 449 Oxycomanthus bennetti 311 oxygen origin 43 in seawater 32, 33 oxygen atoms 30 Oyashio Current 59, 457, 460 oyster Atlantic thorny 280 black-lip pearl 280 European, over-exploitation 279 oyster plant 243 oyster thief 238 oyster toadfish 349 oystercatcher, Eurasian 378, 394 oysters Chesapeake Bay 116 pearl formation 277 Ozbourn Seamount 476, 481

P P’enghu Liehtao 464 Pachyptila turtur 388 Pacific angel shark 326 Pacific blackdragon 347 Pacific gray whale 123, 460 Pacific grenadier 349 Pacific hagfish 319 Pacific halibut 123 Pacific Ocean 456–57, 467, 468, 469, 477, 478, 479 circulation 456, 457 depth 169 El Niño/La Niña 68–69 Northwestern 460–61 ocean basin 456 Ring of Fire 174, 184, 456, 458 temperature 34 winds 457 Pacific Plate 184, 423, 456, 458, 460, 469, 472, 473, 480 Pacific razor clam 129 Pacific reef egret 390 Pacific salmon 459 Pacific stilt-mangrove 252 Pacific-Antarctic Rise 480 Pacific–Antarctic Ridge 422, 457, 483 pack ice 198 packhorse lobster 15 paddle weed 251 paddle worm, green 274 Padina gymnospora 238 Padre Island 117, 440 Paelopatides grisea 223 Pagodroma nivea 388 Pagophila eburnea 397 Pagophilus groenlandicus 404 Pagurus prideaux 267 painted ray 333 Pakicetus 228 Palaeo-Tethys Sea 44, 45 Palaeogene, ocean life 228 Palaeomon serratus 296 Palau 456 Palau Sumba 472 Palau Trench 465, 466 Palawan 465 Palawan Trough 465 Palk Strait 450 palm, coconut 243, 253 Palmas, Cape 443 Palmeirinhas, Ponta das 443 Palmerston 476 Palmyra Atoll 476 Palos, Cabo de 438 Panama Basin 478 Panama Canal 440, 441, 444 Panama Fracture Zone 478 Panama, Gulf of 478 Panay 465, 466 pancake ice 198, 427 Pandion haliaetus 393 Pandora Bank 473 Pangea 44, 45 Panikkar Seamount 449 Pantar Island 160 Panthalassic Ocean 44 Panulirus argus 297 Papakolea Beach see Green Sand Beach, Mahana Beach Papua Plateau 472 Papua, Gulf of 472 Papuan swiftlet 135 Parablennius gattorugine 364 Paracel Islands 465 parallel evolution 45 parasitic jaeger 398 parasitism 217, 292 Parazoanthus anguicomus 270 Paría, Gulf of 441 Parker Seamount 459 Parnaíba Ridge 442 parrotfish green humphead 361 humphead 160 Parry Islands 424, 425, 426

503

504

INDEX Passamaquoddy Bay 80 passion flower feather star 311 Patagonian Ice Sheet 46 Patagonian Ice-fields 103 Patagonian Shelf 444, 445 patch reefs 152 Pate Island 454 Patella vulgata 284 Patton and Gilbert Seamounts 459 Patton Escarpment 469 Patton Seamount 459 pea crab 217, 300 peacock mantis shrimp 295 peanut worm 313, 314 Pearl and Hermes Reef 468 Pearl River Estuary 122 pearlfish 349 pearls, formation 277 pebbles, beach 107 Pecten maximus 280 pedicellariae, sea urchin 307 pedicle 315 Pedro Bank 441 Pedro Escarpment 441 Peel Sound 424, 426 Pegea confoederata 319 Pelagia noctiluca 263 pelagic sea birds 378 pelagic zone 164–65 Pelamis platurus 374 Pelecanoides urinatrix 389 Pelecanus occidentalis 391 pelican Australian, Coorong Lagoon 121 brown 214, 379, 380, 391 pelicans 380 Peloponnese 439 Pemba 446, 454 penguin 380 adelie 379 chinstrap 383 emperor 190–91, 192–93, 379, 383, 384–385 Galapagos 218 jackass 383 king 382 little 383 macaroni 383 Magellanic 383 rockhopper 444 penguins 380 Peninsula Brunswick 444 Péninsule d‘Ungava 426 Pennell Bank 485 Penrhyn 476 Penrhyn Basin 457, 476 Pentecost 473, 481 Penzhinskaya Guba 461 Periclemenes brevicarpalis 296 Periclimenes soror 308 peridotite 42 period, wave 76 Periphylla periphylla 262 periwinkle common 285 marsh 127 Pernambuco Basin 429, 442 Pernambuco Plateau 442 Pernambuco Seamounts 442 Persian Gulf 446, 448, 449 Peru Basin 422, 423, 447, 457, 479 Peru–Chile Trench 423, 457, 478, 479 Peruvian anchoveta 344 Peruvian Current 66, 344, 457 see also Humboldt Current Pervenets Canyon 458 Peter I Island 484 Peters Ridge 459 petrel bonin 388 common diving 389 Leach’s storm 389 snow 388 southern giant 388 Wilson’s storm 389 petrels 380

Petrobius maritimus 304 Petrocelis cruenta see Mastocarpus stellatus Petrolisthes lamarckii 297 Petromyzon marinus 319 Phaethon aethereus 390 Phalacrocorax bougainvillii 392 Phalacrocorax carbo 393 phalarope, red 380, 395 Phalaropus fulicarius 395 Pheonix Islands 457 Philippine Basin 422, 456, 465, 466, 467 Philippine Plate 464, 467 Philippine Sea 422, 456, 464, 465, 466, 467 Philippine Trench 456, 465, 466 Philippines 422, 456 Phoca vitulina 404 Phocoena phocoena 418 Phoebastria albatrus 386 Phoebastria nigripes 386 Phoebetria palpebrata 386 Phoenix Islands 476 Pholas dactylus 281 Phoronis hippocrepia 314 phosphates, in seawater 33 phosphorescence 225 Photoblepharon palpebratum 352 photocytes 224 photophores 36, 224, 233, 289, 346, 347 photosynthesis 36, 248 early Earth 43, 226 oxygen production 33 sunlit zone 168, 169 Phycodurus eques 356 Phyllidia pustulosa 22-23 Phyllospadix 151 Phymatolithon calcareum 245 Physeter macrocephalus 412 phytoplankton 214 at seamounts 174–75 Barents Sea 427 food chain 33, 199, 212, 213 Antarctic Convergence 201 photosynthesis 36 sunlit zone 169–70 surface layer 168 see also diatoms; dinoflagellates; microalgae Pichavaram Mangrove Wetland 134 Pico 436 Pico del Teide volcano 437 Pico Fracture Zone 436 piddock, common 281 pied avocet 394 pied kingfisher 399 Pierre Brazza Seamounts 443 piked dogfish 325 pilchard, South American 344 pillow lava 185, 456 pilot whale, long-finned 418 pilotfish 360 pinch bug 175 Pinctada margaritifera 280 pineapplefish 352 pink lace bryozoan 305 Pink Sands Beach 108 pinnipeds 400–401 early 228 Pinnothere pisum 300 Pioneer Fracture Zone 469 pipefish greater 146 harlequin ghost 356 snake 356 piracy, Strait of Malacca 450 Pisces IV submersible 173 Pisonia grandis 253 Pitcairn Island 457, 477 Piton de la Fournaise 455 Placentia Bay 431 placoderms 227 placodonts 228 plaice 366 plain abyssal 176, 177, 182 sediment 140, 182

planetesimals 40 plankton 170, 214, 317 bioluminescent 225 classification 207 see also phytoplankton; zooplankton plankton cycle 164 plants aquatic 243 beach 242 classification 207 coastal 250 dune 243, 250 flowering 146, 250 intertidal 243 marine 242–43 diversity 242 plate tectonics Cambrian 44 Carboniferous 44 Cretaceous 45 Devonian 44 Eocene 45 Jurassic 45 ocean floor 48–49 platelets, ice 198 plates tectonic 44–45, 174, 183, 423 boundaries 48–49 Ring of Fire 184 platforms, wave-cut 89 Plectaster decanus 308 Plectorhinchus chaetodonoides 359 Plenty, Bay of 481 plesiosaurs 228 Pleuronectes platessa 366 Pliny Trench 439 pliosaurs 228 Plotosus lineatus 345 plownose chimera 324 plover, gray 394 plumose anemone 267 plunge divers (sea birds) 378–79, 391 plunging breakers 77 see also barrel waves, tube waves Pluvialis squatorola 394 pneumatophore 130 pocket beach 109, 112 Pockington Trough 472, 473 pogonophoran worm 315 Pohnpei 467 Poinsett, Cape 483 polar bear 25, 199, 402 threat of global warming 91 polar cells 54 polar easterlies 54, 425 Pole Plain 425 polka-dot batfish 350 Pollicipes polymerus 294 pollution Chesapeake Bay 116 coastal 141 coral reefs 153, 155, 156 Curoman Lagoon 119 Ebrié Lagoon 121 effect on yellow splash lichen 255 Exxon Valdez oil spill 459 Klaipeda Strait 119 New Guinea mangroves 135 Nusa Tenggara 160 Pearl River Estuary 122 Venetian Lagoon 120 Poluostrov Kanin 427 Poluostrov Taymyr 425 Poluostrov Yamal 425 Polybranchid 286 polychaetes 274 polyclad flatworms see flatworms Polynesia 457, 476, 477 polynyas 199 Polyprion americanus 358 polyps, reef-building coral 153, 260 Pomeranian Bay 433 Pompeii worm 171, 275 Poor Knights Islands 150 poppy, yellow horned 252 porcelain crab 291, 297, 298–299

Porcupine Bank 432, 437 Porcupine Plain 429, 436 Porcupine Seabight 437 porcupinefish 367 Porites lobata 268 pororoca tidal bore 118 Porphyra dioica 245 Porpita porpita 262 porpoise, harbor 418 Port Jackson shark 327 Porthcurno Beach 109 Portlock Bank 459 Portuguese man-of-war 214, 256 Portunus pelagicus 301 Posidonia australis 150 Posidonia oceanica 251 post-glacial rebound 88, 96 Postelsia palmaeformis 238 potassium, in seawater 32 potato grouper 358 Pourtales Escarpment 441 Powell Basin 444, 484 Pratt Seamount 459 prawn common 296 deep sea red 296 prawn farming 296 Precambrian, ocean life 226 precipitation 64–65 predators, top 212 predatory comb jelly 317 pressure underwater 35, 171 deep-sea animals 171, 222 pressure-system winds 55 effect of El Niño/La Niña 68–69 Prestrud Bank 485 prevailing winds 54, 58 priapula worm 314 Priapulus caudatus 314 Pribilof Islands 458 prickly redfish 312 primary consumers 212 primary producers 212 Prince Albert Peninsula 424, 426 Prince Albert Sound 424, 426 Prince Charles Island 426 Prince Edward Fracture Zone 446, 482 Prince Edward Islands 431, 446, 482 Prince of Wales Island 424, 426, 459 Prince of Wales Strait 426 Prince Patrick Island 424, 426 Prince Regent Inlet 424, 426 Prince William Sound 459 Príncipe 443 prion, fairy 388 Prionace glauca 332 Pristiophorus cirratus 326 Pristis pectinata 333 Pro-Form racing yacht 57 proboscis monkey 135 Prochloron, symbiosis with Colonian Sea Squirt 319 producers, primary 212 productivity 213 Proliv Longa 424 Proliv Vil’kitskogo 425 Prosqualodon davidi 228 Prostheceraeus vittatus 271 Protector Basin 444 Protector Shoal 445 protists 207, 214, 234 protoplanetary disc 40 Providence Reef 454 Prydz Bay 447 Pseudanthias squamipinnis 358 Pseudobiceros bedfordi 272 Pseudobiotus magalonyx 316 Pseudobiotus water bear 316 Pseudoceros dimidiatus 272 Pseudoceros imitatus 272 Pseudocolochirus violaceus 312 pterobranch worm 314 Pterodroma hypoleuca 388 Pterois volitans 357

pteropods 180, 181 pterosaurs 228 Ptilometra australis 311 Ptilosarcus gurneyi 266 Ptolemy Seamounts 439 Puerto Rico Trench 169, 183, 428, 429, 441 pufferfish, star 367 puffin, Atlantic 399 Puffinus gravis 389 Puffinus tenuirostris 389 Puget Sound, glaciation 102 Pukapuka 476 Punalu’u Beach 112 Punta Gallinas 441 Punta Patiño Nature Reserve 135 Puperita pupa 284 purple sea fan 156 purple sea urchin 310 Pusa hispida 404 pygmy seahorse 357 Pygoscelis antarctica 383 Pyrenocollema halodytes 255 pyrosome, giant 256, 319 Pyrostremma spinosum 319 Pyura spinifera 319

Q Qamar, Ghubbat al 449 Qeqertarssuaq 425, 426 Qeshm 449 quartz 42 shocked 116 quaternary consumers 212 Quebrada Fracture Zone 478 queen angelfish 154, 359 Queen Charlotte Islands 457, 459 Queen Elizabeth Islands 423, 424, 425, 426 Queen Maud Gulf 424, 426 queen scallop 140 Queensland Plateau 472 Quest Fracture Zone 444 quicksand Alaskan mudflats 129 Morecambe Bay 127 QuikScat satellite 187 Quinn Seamount 459 Quôc 465

R Rabaul caldera, New Britain 472 rabbit fish 324 Race, Cape 431 racing, ocean yacht 56–57 Radarsat satellite 187 radioactive decay 40 radiolarians 181, 234, 237 radula 278 Rae Strait 424, 426 rafting, ice 195, 198 ragged tooth shark see sand tiger shark ragworm, king 275 ragworms 217 Rai’atea, Society Islands 161 rail clapper 127 flightless 158 zapata 133 rainbands 70 rainfall 64 raised beach 89, 96 Raja undulata 333 Ralik Chain 467 Ramalina siliquosa 255 Raman Guyot 449 Rapa Nui see Easter Island Rarotonga 476, 477 Rat Islands 458 Ratak Chain 467 ratfish, spotted 324

INDEX Rathlin Island 81 Raukumara Plain 481 ray eagle 158, 160, 204 manta 158, 160, 335 painted 333 spotted eagle 335 rays anatomy 322 reproduction 323 Raz, Pointe du 437 razorfish 357 Ré, Île de 437 rebound, post-glacial 88, 96 Recurvirostra avosetta 394 recycling, nutrient 212 red abalone 284 red bandfish 359 red coral, Mediterranean 266 red crab, migration 302, 303 red mangrove 130, 132 red phalarope 380, 395 Red Sea 422, 446, 448 coral reefs 158 Red Sea Fault Coast 98 Red Sea lionfish 158, 210 red seaweeds 244–45 red tide toxin 164, 236, 237 red-billed brush-turkey 135 red-billed tropicbird 390 red-breasted merganser 381 red-breasted paradise kingfisher 135 reddish egret 132 redfish Laguna Madre 117 prickly 312 Reed Bank 465 reef crest 154–55 reef flat 154, 155 reef hermit crab 297 reef lizardfish 347 reef zones 154–55 reef-forming sponge 260 reefs coral 152–55 biodiversity 154–55 cold-water 179 destruction 155, 160 formation 153 warm-water 153 zones 154–55 reflective beach 106, 107 refraction, wave 77 Regalecus glesne 348 Regan’s angler 351 Reinga Ridge 481 Reinga, Cape 481 Remotely Operated Vehicle (ROV) 173 Global Explorer 172 Hercules 173 Renaud Island 484 Rennell 473 reproduction, animals 257 reptiles 368–69 anatomy 368 classification 209, 369 exploitation 368 feeding 368 giant, Mesozoic 228 habitat 368 reproduction 369 Researcher Seamount 441 residence time, ion 32 Resolution Island 426 reticulate whipray 333 retreat, managed 105 Réunion 446, 454 Réunion, hot spot 49, 455 Revillagigedo Islands 469 Reykjanes Basin 423, 429, 430 Reykjanes Ridge 423, 429, 430 Rhabdopleura compacta 314 Rheic Ocean 44 rhesus macaque 134 Rhinobatos lentiginosus 333 Rhinochimaera pacifica 324 Rhinocodon typus 328 Rhinomuraena quaesita 342

rhinophores 286 Rhir, Cap 437 rhizoids 249 Rhizophora stylosa 252 Rhodes 439 Rhodes Basin 439 Rhodophyta 244 Rhône Fan 438 rias 88 Devon Coast 96 Falmouth Bay 148 Tasmania 88 ribbed mussel 127 ribbon eel 342 ribbon worm 273 Richardson Hills 441 ridges mid-ocean 42, 174, 182, 185 and sea-level change 88 ridging, ice 198 Rifleman Bank 465 rift shrimp 189 Riftia pachyptila 315 rifting 44–45 Red Sea 44, 98 Riga, Gulf of 433 right whale 408 Southern, migration 417 Riiser–Larsen Ice Shelf 192–93, 484 Ring of Fire, Pacific Ocean 174, 184, 456, 458 ring-tailed cardinal fish 359 ringed seal 404 Rio de la Plata 118 Rio Grande Fracture Zone 423, 429 Rio Grande Rise 423, 429 Rio Jacui 117 rip currents 110 ripples 76 rise, continental 177 Rissa tridactyla 397 Risso’s dolphin 414 Ritchie Bank 454 river lamprey see lampern Rivera Fracture Zone 469, 478 rivers Amazon 118, 440, 65 Ambodibonara 134 Amur 65 Brahmaputra 134, 450 Changjiang see Yangtze Chao Phraya 465 Coleroon Estuary 134 Congo 114, 443 Danube 439 Digul 135 Dordogne 120 Gambia 120 Garonne 120 Ganges 134, 177, 450 Huang He see Yellow River Humber 119 Indus 448 Kikori 135 Komoë Lena 200, 424 Limpopo 158 Mackenzie 63 Mississippi 116 Murray 121 Neman 119 Niger 443 Nile 97 Orange 443 Ouse 119 Paraná 118 Pearl 122 Plate Estuary 118 St. Lawrence 116, 431 Scheldt 104, 119 Susquehanna 116 Trent 119 Uruguay 118 Vellar 134 Xi Jiang 122 Yangtze 122, 464 Yellow 464 Roaring Forties 54

robber crab 158, 297 Robbie Ridge 476 Robertson Island 484 Roca, Cabo de 437 Rochebonne, Plateau de 437 Rocher Percé 431 rock springtail 304 Rockall 430, 432 Rockall Bank 429, 430, 432 Rockall Trough 432 Rocket, Sea 242 rockhopper penguin 444 rockling, shore 349 rocks formation 42 igneous 42 metamorphic 42 seabed 142–43 sedimentary 42 Rodgers Seamount 442 Rodinia 44, 227 Rodrigues 447, 455 Rodrigues Ridge 455 Rodsand II 435 Roe Bank 450 Roes Welcome Sound 426 Roggeveen Basin 423, 457, 479 rogue waves 76 Romanche Fracture Zone 429, 442 Ronne Basin 484 Ronne Ice Shelf 423, 483, 484 Ronne–Filchner Ice Shelf 192 Roo Rise 451 Roosevelt Island 483, 485 rorquals 409 Rosalind Bank 441 roseate spoonbill 132 Rosemary Bank 430, 432 Ross Bank 485 Ross Ice Shelf 192, 422, 457, 483, 485 Ross Island 485 Ross Sea 422, 457, 483, 485 Ross, Sir James Clark (1800–62) 192, 485 Røst Bank 425, 427, 433 Rothschild Island 484 rotifers 317 roughy, orange 175, 353 round stingray 334 roundworm 314 ROV see remotely operated vehicle (ROV) Rowley Shelf 447, 451, 472 Rowley Shoals 451, 472 Royal Bishop Banks 465 Royal Charlotte Bank 442 Royalist Bank 465 ruddy turnstone 395 Rugen 433 Ruppert Coast 485 Ruppia maritima 148 Rydberg Peninsula 484 Rynchops niger 398 Ryukyu Islands 464, 465, 466 Ryukyu Ridge 464, 466 Ryukyu Trench 422, 456, 464, 465, 466, 467 Ryurik Seamount 449

S “sea gliders” 187 “stingray city” 335 Saaremaa 433 Saba Bank, biodiversity 211 Sabellaria alveolata 275 Sabellastarte magnifica 275 Sable Island 431 Sable, Cape 431 sablefish 176 saccoglossans 247 Saccopharynx lavenbergi 343 Saccorhiza polyschides 148 Sacculina 217, 290 Sado 464 Sado Ridge 461, 464

Saemangeum Wetlands 129 Saffir–Simpson scale (hurricane categories) 71 Sagar Kanya Seamount 449 Saguenay Fiord 116 Sahul Banks 451, 472 Sahul land bridge 46 Sahul Shelf 447, 451, 472 Sailfish, Atlantic 365 sailing long-haul 55 ocean yacht racing 56–57 sailor’s eyeball 247 Saint Elias, Cape 459 Saint Helena 443 Saint Helena Fracture Zone 429, 443 Saint Lawrence Island 458 Saint Matthew Island 458 Saint Paul Fracture Zone 429, 442 Saipan 466 Sakhalin Island 460 Sakhalinskiy Zaliv 461 Sakishima-shoto 464, 466 Sala y Gomez 479 Sala y Gomez Ridge 457, 479 Saldanha Bay 148 Salicornia europaea 251 Salinas, Ponta das 443 salinity 35 Arctic Ocean 65 Baltic Sea 432 Black Sea 439 Coorong Lagoon 121 Dead Sea 35 early oceans 43 Eastern Mediterranean 438 epicontinental seas 45 and freezing point of seawater 35 Gulf of Mexico 440 Gulf of Thailand 465 inverse estuary 122 Laguna de Términos 148 under ice shelves 193 and underwater circulation 60 see also salt, in seawater Salisbury Island 426 Salmo salar 346 salmon 339 Atlantic 346 coho 346 migration 220 Pacific 459 salmon farming 336, 346 salp 319 salt in seawater 32, 35 see also salinity salt harvesting, Guérande 128 salt marsh moss 249 salt marshes 124–25 Bay of Fundy 124 biodiversity 125 Cape Cod 126 conservation 125 fauna 125 formation 124 Guérande 128 Minas Basin 126 Morecambe Bay 127 Saemangeum Wetlands 129 South Carolina Low Country 127 the Wash 128 Wadden Sea 127 zones 124 salt pans, Guérande 128 salt-wedge estuary 114, 116, 118 saltation 107 Saltenfiord 81 saltmeadow cordgrass 126 Saltstraumen, tidal race 81 saltwater crocodile 135,136–37, 369, 377 saltwater, global 64 Salûm, Gulf of 439 Salvelinus alpinus 346 Samar 465, 466

Samoa 457 Samoa Basin 457, 476 samphire, marsh see common glasswort San Agustin, Cape 465, 466 San Andreas Fault 123, 469 San Andrés Trough 441 San Cristobal 473 San Francisco Bay 123, 469 influence of California Current 67, 469 tide rip 82 San Lucas, Cabo 469 San Martin Canyon 484 San Pablo Bay 123 sand beach 107 black volcanic 112 seabed 144 sand belt, Nile Delta 97 sand bubbler crab 290 sand crocus 242 sand dollar 306, 310 sand dunes 107 Banc d’Arguin 110 Cap Ferret 110 Curonian Spit 119 destabilization 113 Ninety Mile Beach 112 North Jutland 109 Oregon National Dunes 113 Skeleton Coast 98, 100–101 stabilization 105 see also marram grass sand eel 364 commercial fisheries 165, 355, 399 sand hopper 295 sand scour 143 sand spits 93, 108, 110 Dungeness Spit 113 sand tiger shark 328 sandflats 124 Minas Basin 126 sandpiper semipalmated 126 spoon-billed 129 Sangir, Kepulauan 465, 466 Santa Cruz Basin 473 Santa Cruz Islands 473 Santa Inés, Isla 444 Santa Isabel 473 Santa Maria 436 Santaren Channel 441 Santorini 439 Santos Plateau 429 São Jorge 436 São Miguel 436 São Roque, Cabo de 442 São Tomé 443 São Vicente, Cabo de 437 Sarawat mountain escarpment 98 Sarcophyton trocheliophorum 264 Sardinia 438 Sardinia Terrace 438 Sardinia–Corsica Trough 438 Sardinops sagax 344 Sargasso Sea 170, 423, 429, 440, 441 European eel 342 Sargassum muticum 239 Sargassum natans 235 sargassum, brown 235 sargassumfish 170, 215, 351 Sarmiento Ridge 479 Sars Bank 444 sastrugi 193 satellite oceanography 186, 187 Envisat 187 Meteosat 187 QuikScat 187 Radarsat 187 Saunders Coast 485 Saury Seamount 441 saury, Atlantic 352 Savai’i 473, 476 Savu Basin 451, 472 Savu Sea 451, 472 sawfish, smalltooth 333

505

506

INDEX sawshark 323 longnose 326 Saya de Malha Bank 455 scales, fish 336 scallop great 280 queen 140 scalloped hammerhead shark 332 Scandinavian Ice Sheet 46 Scarba 81 scatterometer 54, 187 scavengers, deep-sea 182, 223 scavenging, herring gull 396 Schistidium maritimum 249 Schoppe Ridge 459 Scilly Isles, influence of North Atlantic Drift 63 Scilly, Isles of 432, 437 sclerites 260 Scomber scombrus 365 Scomberesox saurus 352 Scorpaena plumieri 358 scorpionfish 216 spotted 358 Scotia Arc 445 Scotia Plate 423, 444, 445 Scotia Sea 423, 429, 444, 445, 482, 484 Scott Canyon 485 Scott Coast 485 Scott Island 485 Scott Seamounts 485 Scott, Cape 459 scour, sand 143 scrawled filefish 366 scrimshaw 401 scurvy-grass 252 Scyliorhinus retifer 329 sea anemones, anatomy 260 sea apple 312 sea arch 92 sea bamboo 148 sea beech 244 seabed rocky 142–43 sandy 144–45 sea birds anatomy 378 breeding 380 classification 380 feeding 379 habitat 378 migration 380 threat from fishing 379 sea bristletail 304 sea butterfly see three-tooth cavoline sea cave 93 sea color 37 sea cow see manatee sea cow, Steller’s 419 sea cucumber 144, 181, 223, 306, 312 sea daisies 306 sea eagle, white-bellied 393 sea fan common 265 purple 156 sea goldie 152–53, 358 sea grapes 247 sea hare 286 sea ivory 255 sea knolls 174 sea krait, yellow-lipped 368, 374 sea lamprey 319 sea lavender 124 common 252 sea lettuce 246 sea lily 223, 306, 311 sea lion Australian 404–405 Californian 403 South American, breeding colonies 401 sea lions, anatomy and physiology 400 sea mayweed 243 sea mouse 144, 274 Sea of Azov 439

Sea of Cortez see Gulf of California Sea of Japan/East Sea 150, 460, 461 Sea of Marmara 439 Sea of Okhotsk 460, 461 sea otter 151, 401, 402 sea oxeye 127 sea palm 238 sea pen 144 orange 266 slender 266 sea pink 250 sea potato 311 sea rocket 242 sea skaters 30 sea slater 295 sea slug chromodorid 286 hermissenda 286 sea slugs 22–23, 247, 277 sea smoke 59 sea snakes 368–69 beaked 374 leaf-scaled 375 olive 375 turtle-headed 375 yellow-bellied 374 sea sparkle 236 sea spider, giant 293 sea spiders 292 sea squirt colonial 319 common 318 star 319 sea stack 93 Marinha Beach 97 Twelve Apostles 20, 99 sea stars 306 sea strawberry 108 sea tulip 319 sea urchin edible 310 long-spined 310 purple 310 sea urchins 142, 306, 310–311 control by sea otter 151 sea walls 105 sea whip, white 265 sea-ice 31, 198–99, 430, 445 Arctic Ocean 63 Atlantic Conveyor 63 cycle 65 Greenland Sea 427 Northwestern Pacific 460 satellite monitoring 187 Southern Ocean 482 sea-level change 45, 88–89 Acadia National Park 94 Big Sur 103 geological past 89 Gruinard Bay 96 rise Bangladesh 91 global warming 91 Pacific islands 91 southeastern USA 91 see also tides sea-star shrimp 308 seafloor spreading 45 and sea-level change 45 seagrass 146, 243, 250 Gazi Bay 149 Laguna de Términos 148 Lombok 149 meadows 117, 146–47 Monteray Bay 151 Shark Bay 150 seahorse camouflage 135 pygmy 357 short-snouted 356 seal Antarctic fur 403 common 404 crabeater 405 elephant 35, 61, 222 Northern 405 gray 119, 404

seal cont. harbor see seal, common harp 404 Kurile Harbor 460 leopard 405 Mediterranean monk 404 New Zealand fur 123 Northern fur 403 ringed 404 South American fur 403 Weddell 199, 222, 405 seal hunting 426 Sealark Fracture Zone 447, 455 seals, anatomy and physiology 400 seamounts 174–75 at divergent plate boundaries 48 Bermuda Platform 156 biodiversity 211 Emperor, Hawaii 468 Gulf of Alaska 459 Pacific Ocean 467 seas, epicontinental 45 seaside moss 249 seasnail, violet 214, 256 seawater chemistry 32–33 density 35 freezing point 198 effect of salinity 35 gases 33 ions 32 nutrients 33 pressure 35 salinity 35 temperature 34 seaweed Cotton’s 245 flaccid green 246 spectacular 245 seaweed zone 142 seaweeds brown 238–39 green 243, 246 anatomy 246 habitat 246 harvesting 151, 235 see also agar gel; alginate extraction red 244–245 anatomy 244 distribution 244 habitat 244 sea beech 244 secondary consumers 212 sediment biogenic 180, 181 Black Sea 439 continental rise 177 continental shelf 144–45 continental slope 176 deep-sea 180 deposition, Nile Delta 97 Humber Estuary 119 mangrove swamps 133, 134 mixed 144 ocean floor 180–81 terrigenous 180 Tigris Euphrates Delta 99 see also mud; sand; silt sediment plain 140, 182 sediment predators 140 sedimentary basins 45 oil deposits 45 sedimentary rock 42 seeps, cold 189 Seine Plain 437 Seine Seamount 437 seismic monitoring 49 Selat Mentawai 451 Semibalanus balanoides 294 semidiurnal tides 78 semipalmated sandpiper 126 Seneca the Younger, hydrologic cycle 65 Senkaku Islands 464, 466 Sepia apama 289 Seram, Pulau 465, 466, 472 Serendip Seamount 449 sergeant major 360 Sermilik Valley 430

serpent star 309 Sesostris Bank 449 seven arm starfish 308 Severnaya Zemlya 422, 425 Seward Peninsula 424, 458 Sewell Rise 450 Seychelles 422, 446, 455 Seychelles Bank 446, 454, 455 Shackleton Coast 485 Shackleton Fracture Zone 444 shad, allis 344 Shakal, Ras 448 Shandong Bandai 464 Shantarskiye Ostrova 461 Sharbithat, Ras 449 shark basking 170, 328 blue 332 bluntnose sixgill 325 caribbean Reef 229 cookie cutter 326 copper 213 frilled 325 goblin 329 gray nurse see shark, sand tiger gray reef 229 Greenland 326 hammerhead 322–23 lemon 323 megamouth 328 Pacific angel 326 Port Jackson 327 ragged tooth see shark, sand tiger sand tiger 328 scalloped hammerhead 332 sharpnose sevengill 325 tawny nurse 327 tiger 332 whale 256, 328 white 329, 330–31 whitetip reef 332 zebra 327 Shark Bay 451 Shark Bay, Western Australia 111, 150 sharks anatomy 322 attacks on humans 110, 329 classification 323 conservation 322 hunting senses 323 reproduction 323 sharpnose sevengill shark 325 Shatskiy Rise 456, 461 Shcherbakov Seamount 451 shearwater great 389 short-tailed 389 wedge-tailed, migration 389 sheathbill, snowy 394 shelduck, common 381 shelf continental 140–41 geology 141 shelf break 176 Shelikhova Zaliv 461 Shelikof Strait 459 Shell Beach, Shark Bay 111 shells, beach 107 Sherard, Cape 425, 426 Shetland Islands 425, 433 Shikoku 456, 461, 464, 466 Shikoku Basin 456, 464, 466 Shikoku Island 83 Shimada Seamount 469 Shinkai submersible 168 Shinkai 6500 submersible 173 Shipunskiy, Mys 458 shipworm 280 shipwrecks diving 475 as habitat 145 Skeleton Coast 98 Shiraho Reef 160 Shirase Coast 485 Shirshov Ridge 458, 461 shoaling fish 256, 338 waves 77

shocked quartz 116 shore bristletail 304 shore rockling 349 short-snouted seahorse 356 short-tailed albatross 386 short-tailed shearwater 389 shrimp anemone 12–13, 296 banded coral 217 giant mussel 295 harlequin, molting 291 peacock mantis 295 rift 189 sea-star 308 spotted cleaner 290 tozeuma 149 shrimp farming 131, 465 shuga 198 Shumagin Islands 459 Shuyak Island 459 Sian Ka’an Biosphere Reserve 132 Siberia Seamount 461 Siberian Ice Sheet 46 Siboglinum ekmani 315 Sicily 438 Sicily, Strait of 438 Sierra Leone Basin 423, 429, 443 Sierra Leone Rise 442 Sigsbee Escarpment 440 Sigsbee Plain 440 silica 181 hydrothermal vents 188 in sponges 258 siliceous ooze 181 silt 180 Alaskan mudflats 129 River Plate estuary 118 Yangtze Estuary 122 see also sediment Silurian, ocean life 227 Simpson Peninsula 424, 426 Sines, Cabo de 437 Singapore Harbor 92 sink carbon 33, 67 ion 32 sinkhole, Great Blue Hole 157 Siphonaria compressa 148 Siple Coast 485 Siqueiros Fracture Zone 478 Sir Edward Pellew Group 472 sirenians 400–401 early 228 Sirius Bank 442 Sirte Rise 439 Sirte, Gulf of 439 Sivuchiy, Mys 458 Sjaelland 433 Skagerrak 432, 433 phytoplankton bloom 33 skate, common 333 skater, marine 292, 304 skates 323 Skeleton Coast 98, 100–101, 443 Skiathos Island 439 skimmer, black 398 Skjerstadfiord 81 Sklinna Bank 433 Skookumchuck Narrows Tidal Race 82 skua, great see parasitic jaeger Skye, Isle of 432 sleeper shark 323 slender sea pen 266 slender snipe eel 342 slipper limpet, sex change 279 Sloane’s viperfish 346 slope, continental 176 Slough-na-more Tidal Race 81 smalltooth sawfish 333 smelt 339, 345 Smetanin Seamount 461 smokers black 188 white 188 smooth cordgrass 124, 126, 127 Smyley Island 484 snake eel, banded 343

INDEX snake pipefish 356 snapper, bluestripe 161, 359 Snares Islands 481 snout infantfish 161 snow petrel 388 snowball events 46 snowfall 64 Snowhill Island 484 snowy sheathbill 394 Society Islands 161, 457, 476 Society Ridge 476 Socotra 446, 449 sodium chloride 32 sodium ions 32 Sodwana Bay, continental slope 176 Sofala, Baia de 454 SOFAR channel 37 Sognefjorden 433 Sohm Plain 423, 429, 441 solar heating 54, 66 Solar System, early 40 soldierfish, whitetip 352 Solea solea 366 solenogasters 279 Solenosmilia variabilis 179 Solenostomus paradoxus 356 solid-state creep 41 Solomon Basin 473 Solomon Islands 456, 472, 473 Solomon Sea 422, 456, 472 Microplate 472 Somali Basin 422, 446, 449, 454 Somali Current 446, 447 Somateria mollissima 381 Somerset Island 424, 426 Somniosus microcephalus 326 Sonmiani Bay 449 sooty albatross 386 light-mantled 386 sooty tern 184 Sorol Trough 466 Soudan Bank 454 Soufrière Volcano, Monserrat 440 Sound Fixing and Ranging channel (SOFAR) 37 Sound of Barra 148 sound, underwater 37 Sousa chinensis 414 South American fur seal 403 South American pilchard 344 South American Plate 423, 442, 444, 479 South American sea lion, breeding colonies 401 South Atlantic Gyre 428 South Atlantic Plate 445 South Australian Basin 422, 447 South Australian Plain 422, 447 South Bank 433 South Carolina Low Country 127 South China Basin 422, 456, 465 South China Sea 422, 456, 465 South East Point 480 South Equatorial Current 442, 446, 447, 451, 455, 456, 473, 477, 479 South Fiji Basin 422, 457, 473, 476, 481 South Georgia 423, 444, 445, 482 South Georgia Ridge 444, 445 South Georgia Rise 445 South Indian Basin 422, 447, 483, 485 South Indian Gyre 446 South Island 457, 481, 483 South Makassar Basin 451 South Orkney Islands 444, 445, 482, 484 South Pacific Gyre 477, 479 South Pole 483 South Sandwich 445 South Sandwich Fracture Zone 482, 484 South Sandwich Islands 444, 445, 484 South Sandwich microplate 445 South Sandwich Trench 183, 428, 429, 445, 482, 484

South Scotia Ridge 444, 445 South Shetland 484 South Shetland Islands 444, 482, 484 South Shetland Trough 444, 484 South Solomon Trench 473 Southampton Island 426 Southeast Indian Ridge 422, 446, 447, 483 Southeast Monsoon 457 Southeast Pacific Basin 423, 457, 483 southern beach moss 249 Southern Cook Islands 457, 476 southern giant petrel 388 Southern Ocean 482–83 circulation 201, 482, 483 depth 169 icebergs 195 ocean floor 482 winds 482, 483 yacht racing 57 southern right whale 408 migration 417 southern stingray 334–35 Southwest Indian Ridge 422, 446, 455 Southwest Monsoon 446, 447 Southwest Pacific Basin 423, 457, 476, 480, 481, 483 Spaatz Island 484 Spanish dancer 287 specific heat capacity 31 spectacular seaweed 245 Spencer Gulf 122 sperm whale 222, 412 spermaceti 412 Spheniscus demersus 383 Spheniscus magellanicus 383 Sphyraena barracuda 365 Sphyrna lewini 332 spider monkey 132 spilling breakers 77 spiny lobster 297 Caribbean, migration 220 spiny-headed blenny 16–17 spiral wrack 234 Spirobranchus giganteus 275 spits, sand 93, 108, 110, 113 Spitsbergen 423, 425, 427 Spitsbergen Fracture Zone 425, 427 Spitzbergen 31 split-fan kelp 148 Spondylus americanus 280 sponge barrel 260 boring 217 breadcrumb 259 coralline 259 flesh 259 lemon 259 Mediterranean math 259 reef-forming 260 tube 154, 259 sponges 260–61 anatomy 260 Spongia officinalis 259 spookfish 324 brownsnout 171 spoon-billed sandpiper 129 spoonbill, roseate 132 spoonworm 313, 314 Sporades 439 sporangia 249 spotted boxfish 366 spotted cleaner shrimp 290 spotted cusk-eel 349 spotted eagle ray 335 spotted garden eel 343 spotted lanternfish 347 spotted ratfish 324 spotted reef crab 300 spotted scorpionfish 358 Spratly Islands 465 spreading, seafloor 45 Spriggina 226 spring tides 79 springtail 290 rock 304

spurdog see piked dogfish Squalus acanthias 325 squat lobster 143, 175, 178, 179 Squatina californica 326 squid bigfin Reef 171, 279 common 289 firefly 36, 224 glass 289 Humboldt 277 vampire 289 Sri Lanka 422, 447 St. George’s Channel 432 St. Helena 185, 442 St. James, Cape 459 St. Lawrence Estuary 116, 431 St. Lawrence Seaway 431 St. Lawrence, Gulf of 429, 431 St. Lucia Channel 441 St. Lucia, Les Pitons 95 St. Ninian’s Tombolo 108 St. Paul Island 447 St. Peter and St. Paul Rocks 442 St. Vincent Channel 441 St.-Malo, Golfe de 432, 437 stack see sea stack stalked jellyfish 262 standing waves 79, 82 star pufferfish 367 star sea squirt 319 Starbuck Island 476 starfish 306 crown of thorns 158, 161, 307, 309 goosefoot 308 seven arm 308 stargazer, common 364 statocyst 317 steamer duck, Magellanic flightless 381 Steele Island 484 Stefansson Island 424, 426 Stegostoma fasciatum 327 Steller’s sea cow 419 Stenella longirostris 414 Stercorarius parasiticus 398 Stercorarius skua 398 Sterna caspia 397 Stewart Island 481 Stewart Seamount 442, 465 stickleback, three-spined 357 stilt fishing 355 stilt-mangrove, Pacific 252 stilt, black-winged 394 stinger, mauve 225, 263 stinging cells 260 stinging hydroid 262 stingray blue-spotted 334 round 334 southern 144–45, 334–35 Stocks Seamount 442 stonefish 142, 357 stony coral 153, 158 stoplight loosejaw 347 Stor Bank 425, 427 Storfjordrenna 425, 427 stork jabiru 131, 132 wood 132 storm tropical 70–71 see also hurricanes storm beach, Chesil Beach 109 storm petrel Leach’s 389 Wilson’s 389 storm surge 71 storm-surge barriers 105 Eastern Scheldt Estuary 104, 119 Strabo Trench 439 Stradbroke Seamount 481 Strait of Dover 433 Strait of Gibraltar 438 Strait of Hormuz 448 Strait of Magellan 444 Strait of Malacca 450 Strait of Messina 82, 438 Strait of Sicily 438

Straits of Florida 440 Straits of Gibraltar, closure 45 stratification, water, Hardanger Fiord 119 striped catfish 256, 345 stromatolites 150, 226, 232 Strombidium sulcatum 236 Stromboli 438 Strongylocentrotus purpuratus 310 sturgeon Beluga 340 European 340 sturgeons 339 Gironde Estuary 120 subduction 44, 48, 183 subduction zone Aleutian Trench 458 Andaman Sea 450 Cascade Range 459 Coral Sea 473 Hikurangi Trench 480 Java Trench 451 Kermadec–Tonga Trench 480 Lesser Antilles volcanic island arc 95 Middle America Trench 478 Northwestern Pacific 460 Pacific Ocean 456 Peru–Chile Trench 479 Philippine Trench 467 Ryukyu Trench 464, 467 South Sandwich Trench 445 Vityaz Trench 473 submarine canyon 176 submarine volcano 50–51 submarine waterfall 182 submersibles 173 Alvin 168, 171, 173, 182–83 C-Quester 173 Deepflight Super Falcon 173 Deep Rover 223 Deepsea Challenger 173 Hercules ROV 173 Pisces IV 173 Shinkai 168, 173 Shinkai 6500 173 Trieste expedition 168, 183, 467 see also remotely operated vehicle subsidence, and sea-level change 88 Sue Ridge 441 Suez Canal 448 Suez, Gulf of 448 sugar kelp 148 Suisun Bay, San Francisco 123 Sula leucogaster 391 Sula nebouxii 391 Sula, Kepulauan 451, 465, 466, 472 sulfate, in seawater 32 sulfides, hydrothermal vents 188 Sulu Archipelago 465 Sulu Basin 465 Sulu Sea 160, 465, 466 Sulzberger Bay 485 Sumatra 422, 447, 451, 456, 465 Sumba, Pulau 451 Sumbawa 451, 472 Sun early Solar System 40 influence on tides 79 Sunda land bridge 46 Sunda Plate 450 Sunda Shelf 422, 451, 456, 465 Sunda Strait 465 Sunda Trench 446, 447, 450, 451 Sundarbans Mangrove Forest 134, 452–453 sunfish, ocean 215, 367 sunlight 36 sunlit zone 168, 169–70, 219 supercontinents 44 Supertubes, Jeffreys Bay 110 surf zone 106 surf-kayaking 82 surface currents 58–59 surface layer 168 surface tension 30, 31

surfing 77 Jeffreys Bay 110 Tamarindo Beach 113 Surtsey 430 Surtsey Island 185, 430 Surveyor Fracture Zone 457, 468 Surveyor Seamount 459 Susquehanna River 116 Suwarrow 476 Svalbard 427 Sverdrup Islands 424, 425, 426 swallow-tailed gull 396 swamps, mangrove 130–31 Swan Trough 440 swash zone 106 swash-aligned beach 106 swell 76 swiftlet, Papuan 135 swimbladder 256, 337 Sydney-to-Hobart Race 57 Symbion americanus 313, 316 Symbion pandora 316 symbiosis benthos 217 colonial sea squirt 319 giant clam 281 green algae 248 Synanceia verrucosa 357 Synchiropus splendidus 364 Synodus variegatus 347 Syntrichia ruraliformis 249 Syringodium filiforme 148 Syvataya 427 Syvataya Anna Trough 425

T table coral 268 Tabuaeran 476 Tachyeres pteneres 381 Tacloban 72, 73 Tadjoura Trench 448 Tadorna tadorna 381 Taeniura lymma 334 Taganrog, Gulf of 439 Tagus Plain 437 Tahiti 161, 457, 476 Taiwan 422, 456 Taiwan Banks 464, 465 Taiwan Strait 422, 456, 464, 465 Takoma Reef 458 Takuyo-daiichi Seamount 461 Talaud, Kepulauan 465, 466 Tamarindo Beach 113 Tanaga Island 458 Tanega-shima 464, 466 Tanimbar, Kepulauan 472 Tanna 473 tapeworm, broad fish 272 Taranto, Gulf of 439 Tarawa 467 tardigrades see water bears tarpon 341 Tasman Fracture Zone 422, 456, 480 Tasman Plain 456, 480 Tasman Plateau 447, 480 Tasman Sea 422, 456, 480, 481 Tasman, Abel (1603–c.1659) 480 Tasmania 422, 447, 456, 480 tasselled wobbegong 327 tasselweed 148 Tatar Trough 461 Tatarskiy Proliv 461 Taupo Tablemount 481 Taurulus bubalis 357 tawny nurse shark 327 Taylor Column 174 teal, Madagascar 134 tectonic estuary 123 tectonic plates 44, 174, 183, 423 boundaries 48–49 ocean floor 48–49 Ring of Fire 184 tectonic uplift, Big Sur 103 Tectus niloticus 284 Tehuantepec Ridge 478 Tehuantepec, Gulf of 478

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INDEX Tehuantepec, Istmo de 440 Tehuelche Fracture Zone 444–45 temperature ocean 34 effect of El Niño/La Niña 68–69 monitoring 69 satellite monitoring 187 and sea-level 88 and underwater circulation 60 water 31 Ten Degree Channel 450 Tenerife 437 Tenerife Island 437 Tephromela atra 255 Teraina 476 Terceira 436 Terceira Rift 437 Terebratulina septentrionalis 315 Teredo navilis 280 tern Arctic, migration 220 Caspian 397 common 128 fairy see tern, white Inca 397 least 126 sooty 184 white 397 Tern Island 468 terraces, marine 89, 103 terrapin, diamond-backed 126 terrigenous sediment 180 Terrington Marshes 128 tertiary consumers 212 Tethys Ocean 45, 438, 439 see also Palaeo-Tethys Sea Tetraselmis convolutae 248 Teuthowenia pellucida 289 Texas-Louisiana Shelf 440 Thailand, Gulf of 456, 465 Thalassarche melanophrys 387 Thalassia testudinum 148 Thalassodendron ciliatum 149 Thelenota ananas 312 thermocline 34 thermohaline processes 60 Theta Gap 437 Thitu Reefs 465 Thomson Trough 481 Thor Iversen Bank 425, 427 Thracian Sea 439 Three Gorges Dam 122 Three Kings Rise 481 Three Points Spur 443 Three Points, Cape 443 three-spined stickleback 357 three-tooth cavoline 286 Thunnus thynnus 365 Thurston Island 483, 484 thysanoon Fflatworm 272 Thysanozoon nigropapillosum 272 Tiagba village, Ivory Coast 121 tidal barriers 105 tidal bores Mascaret 120 pororoca 118 tidal currents 79 tidal flats 124 Alaskan 129 Minas Basin 126 Morecambe Bay 127 Saemangeum Wetlands 129 South Carolina Low Country 127 The Wash 128 Wadden Sea 127 Yatsu-Higata 129 tidal power 428 tidal races 79, 80–83 tide rip 79, 82 tides 76, 78–79 diurnal 78 monthly cycle 79 neap 79 semidiurnal 78 spring 79 see also waves, ocean Tierra del Fuego 444 tiger cowrie 285

tiger shark 332 tiger, Bengal 134 Tigris Euphrates Delta 99 Tiki Basin 423, 457, 477 Tiktaalik roseae 227 Timbue, Ponta 454 Timor 447, 451, 456, 472 Timor Sea 422, 451, 472 oil deposits 451 Timor Trough 451, 456, 472 Tinaca Point 465, 466 Tinian 466 Tinro Basin 461 Tinro Rise 461 Tintamarre Spur 441 titan triggerfish 366 predator of long-spined sea urchin 310 Titanic disaster 196, 197, 431 toad, natterjack 125 toadfish, oyster 349 Tobago 441 Tobago Basin 441 Todirhamphus chloris 399 Tohoku tsunami 49, 462–463 Tokyo Bay, Yatsu-Higata tidal flat 129 Tolo, Teluk 451 Tomaszeski Seamount 476 tombolo (sand spit) 106, 108, 109 Tomini, Gulf of 451, 465, 472 tompot blenny 364 Tonga 457 Tonga Ridge 473, 476, 480, 481 Tonga Trench 422, 457, 473, 476, 477, 481 Tongatapu Group 473, 476, 481 Tongking, Gulf of 465 Tongue of the Ocean 441 Tonicella lineata 289 top predators 212 top shell 284 Torpedo nobiliana 334 Torres Seamount 478 Torres Strait 472, 473 Torsk 349 Tortuga, Isla de 441 toucan, keel-billed 132 tourism diving 475 Lombok 149 Red Sea 158, 475 Sian Ka’an Biosphere Reserve 132 toxin, red tide toxin 236, 237 Toxopneustes pileoulus 310 Toyama Seamount 461 Toyama Trench 461 tozeuma shrimp 149 Trachinus draco 364 trade winds 54, 428, 447, 457 Traena Bank 433 Traena Deep 433 transform faults 442 Easter Island Fracture Zone 479 transform plate boundary 48 Transkei Basin 446 Transpolar Current 200, 201, 424, 425 trawling, damage to deep-water reefs 179 trenches, ocean 48, 183 Triaenodon obesus 332 Triassic, ocean life 228 Trichechus manatus 419 Trichechus senegalensis 418 Trichodesmium erythraeum 233 trichomes 233 Tridacna gigas 281 Trieste expedition 168, 183, 467 triggerfish titan 366 predator of long-spined sea urchin 310 trilobites 227 trimarans, ocean yacht racing 57 Trindade, Ilha da 442 Trinidad 441

triple junction Azores 437 Gulf of Guinea 443 Indian Ocean 446 tripodfish 223, 347 Trisopterus luscus 348 Tristan da Cunha 185 trochophore, ciliated 279 Tromelin 454 Trondheimsfjorden 433 tropical feather star 311 Tropical Rainfall Measuring Mission 187 tropicbird, red-billed 390 trumpetfish 356 tsunamis 49 2004 Indian Ocean 49, 134, 159, 450 Peru–Chile Trench 479 risk, La Palma Island 437 warning systems 49 Tohoku 462–463 Tsushima 460, 464 Tsushima Basin 460, 464 Tsushima Current 150, 464 Tuamotu Fracture Zone 457, 477 Tuamotu Islands 423, 457, 476, 477 Tuamotu Ridge 457, 476 Tubbataha Reefs 160 tube anemone 177, 270 tube feet 306, 308 tube sponge 154, 259 tube worm, giant 315 tube-riding 77, 110 tubeworm, vent 189 Tubipora musica 264 Tubulanus annulatus 273 Tufts Plain 457 tuna, northern bluefin 365 Tungaru 467, 473 tunicates, anatomy 318 Tunisian Plateau 438 Turbanella species 316 turbidity currents 176, 431 turkeyfish see lionfish turnstone, ruddy 395 Tursiops truncatus 414 turtle Atlantic Ridley 371 eastern box 126 flatback 371 green 112, 158, 370 importance of seagrass 146 hawksbill 158, 370, 372–73, 474 hazard from fishing 355 leatherback 113, 371 migration 220 loggerhead 370 turtle-headed sea snake 375 turtles 368–69 tusk shells 279 Tutuila 476 Twelve Apostles sea stacks 20, 99 twilight zone 168, 170, 219 Tylosaurus crocodiles 352 typhoons 70–71 East China Sea 464 Haiyan 72–73 Philippine Sea 467 see also hurricanes Tyrrhenian Basin 438 Tyrrhenian Sea 438

U Uca vocans 301 Udintsev Fracture Zone 423, 457, 483 Udskaya Guba 461 Ulithi 465, 466 Ulm Plateau 458 Ulothrix flacca 246 Ulva lactuca 246 Umboi Island 472

Umnak Island 458 Umnak Plateau 458 Unalaska Island 458 undersea volcano see submarine volcano Ungava Bay 426 unicornfish, bignose 364 Unimak Island 458 Union Reefs 465 United Nations Convention on the Law of the Sea 177 uplift land 88–89 tectonic Big Sur 103 Huon Peninsula 102 Upolu 473, 476 upside-down jellyfish 264 upwelling 60 nutrient 33, 60, 213 at seamounts 174 effect of El Niño/La Niña 68–69 St. Lawrence Estuary 116 Peru–Chile Trench 479 urchin, flower 310 urchins sea 142, 310–11 control by sea otter 151 Uria aalge 398 Urolophus halleri 334 Ursus maritimus 402 Urticinopsis antarctica 267 Uruguay Canyon 484 US, southeast, predicted sea-level rise 91 USS Nautilus 199, 424

V Vaceletia ospreyensis 259 Valencia Basin 438 Valencia Trough 438 Valencia, Golfo de 438 valleys, drowned 88, 148 Valonia ventricosa 247 vampire squid 289 Vampyroteuthis infernalis 289 Vancouver Island 423, 457, 459 Vancouver, George (1757–98) 102 Vanua Levu 473, 476 Vanuatu 457, 473 Varanus indicus 377 Varanus salvator 377 Vava’u Group 473, 476, 481 Vavilov Seamount 438 veliger larvae 279 Vellar Estuary 134 velvet belly lanternshark 326 velvet crab 292 velvet horn 247 Vema Fracture Zone 429, 447, 455 Vema Gap 441 Vembanad Lake 121 Vendée Globe Challenge 57 Venezuela, Gulf of 441 Venezuelan Basin 441 Venice flooding 90 Lagoon 120, 438 Venice, Gulf of 438 Vening Meinesz Seamounts 451 venom beaked sea snake 374 box jellyfish 264 crown of thorns starfish 307 fire urchin 307 flower urchin 307 pedicellariae 307 rabbit fish 324 vent tubeworm 189 vents hydrothermal 32, 185, 188–89 archaea 232 East Pacific Rise 478 fauna 189 Pompeii worm 171

Venus Comb 284 Venus’s Girdle 317 Vereker Banks 465 Verne, Jules (1828–1905) 80 Veron, Charlie (born 1945) 268 Verrucaria maura 254, 255 Verrucaria serpuloides 254 vertebrates 256 Vestfjorden 425, 427, 433 Vesuvius 438 Vibrio fischeri 233 Victoria Harbor, Hong Kong 99 Victoria Island 423, 424, 426 Victoria Land 485 Viking Bank 433 Viking Trough 430, 432 Vilanandra, Tanjona 454 Vincennes Bay 483 violet seasnail 214, 256 violet-spotted reef lobster 230– 31 viperfish, Sloane’s 346 Virgin Passage 441 Virgularia mirabilis 266 Virik Bank 485 Viscount Melville Sound 426 Viscount Melville Strait 424 Viti Levu 473, 476, 481 Vityaz Trench 473 Vlieland Bank 433 Vohimena, Tanjona 454 Volcán Bank 441 volcanoes Andean 43 Andes 479 at convergent plate boundaries 48 Capelinhos, Azores 437 Gulf of Guinea 443 Hawaii 103, 468 Indian Ocean 455 island chains 49, 464, 468, 480 Java Trench 451 Les Pitons, St. Lucia 95 Lesser Antilles 440 and mass extinction 229 Mediterranean 438, 439 Melanesia 472, 473 Middle America Trench 478 Mount St. Helens 459 as origin of water 43 Pacific Ocean 456 Pico del Teide, Canary Islands 437 Polynesia 477 Ring of Fire 184 Sea of Okhotsk 460 South Sandwich Islands 445 submarine 50–51 undersea 50–51, 174 Volvo Ocean Race 57 von Karman vortices 52–53 Voring Plateau 425, 427, 429, 433 Voronin Trough 425 vortices 79, 80–81, 83 von Karman 52–53 Vostok Island 476 Vridi Canal 121

W Wadden Sea 127 waders 380 Wakame (Asian Kelp) 150 walrus 403 Waminoa species 271 wandering albatross 387 warm currents 66 warm-water coral 153 warming, ocean 192 Wash, the 128 water behavior of light 36–37 density 31 global reservoirs 64 heat capacity 31

INDEX water cont. molecules 30–31 origin 43 properties 30–31 as solvent 32 stratification, Hardanger Fiord 119 surface tension 30 three states 31 water bear Echiniscoides 316 Pseudobiotus 316 water bears 313 water cycle, global 64–65 water flea 293 water monitor 134, 377 water quality, Chesapeake Bay 116 water striders 30 water twister 31 water vapor, early Earth 43 waterfall, submarine 182 waterspouts 71 wave-cut platforms 89 wave-erosion 93 wavelength 76 waves barrel 28–29 breaking 77 giant, effect of El Niño 68 internal 76 ocean 76–77 generation 76 propagation 76 properties 76 refraction 77 rogue 76 shoaling 77 standing 79, 82 see also tsunamis Weddell Sea 484 Weddell Seal 199, 222, 405 wedge-tailed shearwater, migration 389 Wegener, Alfred (1880–1930) 44, 45 Wellington, New Zealand, tides 79 West African manatee 418 West Indian manatee 419

West Mariana Basin 467 West Mariana Ridge 467 West Wind Drift 482 westerlies 54, 425, 428, 447, 457 Western Algarve, marine erosion 97 Western Interior Seaway 45 Western Mediterranean 438 whale beluga 116, 199, 413 migration 221 blue 412 migration 417 bowhead 408, 417 cuvier’s Beaked 413 gray 408 migration 417 humpback 408, 410–11, 416 feeding 200–201 migration 417 song 37, 409 killer 415 minke 409 narwhal 421 northern bottlenose 413 northern right 408 Pacific gray 123, 460 pilot, long-finned 418 southern right 408 migration 417 sperm 222, 412 white see whale, beluga whale shark 256, 328 whale song 37, 409 whale stranding 418 whale watching 123, 417 whales early 228 echolocation 37, 400 migration 417 navigation 417 whaling 401, 408 Faroe Islands 418 South Georgia 445 whelk, dog 284 whimbrel 395

whip coral 270 whipray, reticulate 333 whirlpools 79, 80–83 Strait of Messina 438 White Cliffs of Dover 96, 180 white mangrove 130, 132 white sea whip 265 white shark 329, 330–31 white smokers 188 white tern 397 white whale see beluga whale white zoanthid 270 white-bellied sea eagle 393 whitetip reef shark 332 whitetip soldierfish 352 Wilson’s storm petrel 389 wind farming 435 Baltic 434, 435 windrows, Langmuir circulation cells 61 winds Arctic Ocean 425 Atlantic Ocean 428 Indian Ocean 447 monitoring 54 ocean 54–55 Pacific Ocean 457 polar northeasterlies and southeasterlies 54, 425, 483 pressure-system 55 effect of El Niño/La Niña 68–69 prevailing 54, 58 von Karman vortices 52–53 Roaring Forties 54 role in wave generation 76 southeast monsoon 457 Southern Ocean 482, 483 southwest monsoon 447 trade 54, 428, 447, 457 westerlies 54, 425, 428, 447, 457, 482, 483 wobbegong, tasselled 327 Woese, Carl (born 1928) 232 wolf-fish 361 wood stork 132 world oceans 422–23

worm bootlace 273 football Jersey 273 ribbon 273 worms ribbon 273 roundworms 313 segmented 274 wrack knotted 239 spiral 234 wrasse ballan 142 cleaner 361 cuckoo 361 reproduction 338 wreckfish 358 wrecks see shipwrecks wren marsh 127 zapata 133 Wuhan Bridge 122

X Xaafuun, Raas 449 Xanthoria parietina 255 Xenia elongata 265 Xestospongia testudinaria 260 Xi Jiang River 122

Y yacht racing 56–57 Yaghan Basin 429, 444 Yaku-shima 464, 466 Yamato Basin 460, 461, 464 Yamato Ridge 460, 461, 464 Yamato Seamount 461 Yangtze Estuary 122, 464 Yap 465, 466 Yap Trench 465, 466 Yatsu-Higata tidal flat 129 Yelcho Canyon 484 Yellow Bluff Tide Rip 82 yellow horned-poppy 252

Yellow River, suspended sand 464 Yellow Sea 422, 456, 464, 466 yellow shrimp goby 364 yellow splash lichen 255 yellow-bellied sea snake 374 yellow-lipped sea krait 368, 374 Yermak Plateau 425, 427 Yolanda, typhoon see Haiyan, typhoon York, Cape 472 Yos Sudarso, Pulau 472 Younghusband Peninsula 121 Yucatan Basin 441 Yucatan Channel 440 Yucatan Escarpment 440 Yucatan Peninsula 440 Yukon River 458 Yupanqui Basin 423, 457, 479

Z Zalophus californianus 403 Zambezi Canyon 454 Zanzibar 446, 454 Zapata rail 133 Zapata Swamp 133 Zapata wren 133 Zapiola Ridge 429 zebra nerite 284 zebra shark 327 Zenkevich Rise 461 Zephyr Bank 476 Zephyr Reef 473 Zeus faber 353 Zheng He Seamount 449 Ziphius cavirostris 413 zircon 42 zoanthid, white 270 zooplankton 181, 214, 317 sunlit zone 169–70 vertical migration 221 zooxanthellae 153, 261 Zostera capensis 148 Zostera marina 148, 150 Zubov Seamount 443, 467

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ACKNOWLEDGMENTS

Acknowledgments Dorling Kindersley would like to thank several people for their help in the preparation of this book. At the American Museum of Natural History, Udayan Chattopadhyay was unfailingly helpful and John Sparks provided many valuable comments on the text and images. Georgina Garner and Erin Richards worked on early versions of the contents list. Frances Dipper and Robert Dinwiddie drew up the original lists of species and physical features described in the catalog sections. Additional design work was done by Janis Utton and Pankaj Sharma. Tamlyn Calitz and Amy Walters provided editorial assistance, and Klara Kayser contributed design assistance. Neil Fletcher did additional picture research for the Birds section. For the revised edition, Dorling Kindersley would like to thank: Sneha Sunder Benjamin and Sonam Mathur for editorial assistance; Duncan Turner, Hector Gonzalez, Sanjay Chauhan, Vansh Kohli, Kanika Mittal, and Divya P.R. for design assistance; Liz Moore for picture research; and Will Lach, Alex Navissi, and Mark Siddall at the American Museum of Natural History. PICTURE CREDITS Dorling Kindersley would like to thank the following for their help in supplying images: Romaine Werblow in the DK Picture Library; All at SeaPics.com; All at FLPA; Jonathan Hamston at OSF; Teresa Riley at Getty Images; All at Alamy Images. KEY: (a-above; b-below/bottom; c-center; f-far; l-left; r-right; t-top)

SIDEBAR IMAGES Corbis: David Keaton (Atlas of the Oceans); Jeffrey L. Rotman (Ocean Environments). Getty Images: National Geographic/Raul Touzon (Ocean Life); Photonica/Anna Grossman (Introduction).

1 Getty Images: Taxi/Peter Scoones. 2–3 Getty Images: Stone/Warren Bolster. 4 Corbis: (tc); Lawson Wood (bc). 4–5 Getty Images: National Geographic/Brian Skerry. 5 Getty Images: Image Bank/Mike Kelly (tc). NASA: Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC (cra). 6–7 FLPA: Minden Pictures/Norbert Wu (Background). 8–9 FLPA: Minden Pictures/Chris Newbert, Carrie Vonderhaar. 10–11 Getty Images: Michele Westmorland. 12–13 Oceanwide Images: Gary Bell. 14–15 Getty Images: Caroline Warren. 16–17 David Hall (www.seaphotos.com). 18–19 Marine Wildlife: Paul Kay. 20 Getty Images: Iconica/John W. Banagan. 21 FLPA: Minden Pictures/Frans Lanting. 22–23 Getty Images: Visuals Unlimited, Inc. / Reinhard Dirscherl. 24–25 Corbis: NASA. 26–27 Corbis. 28–29 Getty Images: Taxi/Jason Childs. 30 Alamy Images: Pictor International/ImageState (bc). DK Images: Frank Greenaway (bl). 30–31 Alamy Images: Hawkeye (c). 31 Alamy Images: Bryan & Cherry Alexander Photography (br). DK Images: (fbl); Brian Cosgrove (bc); Zena Holloway (bl). NASA: GSFC/ MODIS Rapid Response Team, Jacques Descloitres (tl); Liam Gumley, MODIS Atmosphere Team, University of Wisconsin-Madison Cooperative Institute for Meteorological Satellite Studies (ca). 32 Alamy Images: David Wall (br). Science & Society Picture Library: Science Museum, London (bl). 33 Alamy Images: PHOTOTAKE Inc./ Carolina Biological Supply Company (bc); Stephen Frink Collection/James D. Watt (ca);Visual&Written SL/Kike Calvo (cra). NASA: Provided by the SeaWiFS Project, Goddard Space Flight Center, and ORBIMAGE (br). 34 NASA: MODIS Instrument Team, NASA Goddard Space Flight Center, (c); The U.S.-French TOPEX/Poseidon mission is managed by JPL for NASA’s Earth Science Enterprise, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena (tr). NASA’s Earth Observatory: Jesse Allen, using JASON-2 data provided courtesy of Akiko Hayashi (NASA/JPL) (tr). 35 Alamy Images: Roger Cracknell (cl); Chris A Crumley (tr). DK Images: Frank Greenaway/

Courtesy of the University Marine Biological Station, Millport, Scotland (crb). SeaPics.com: Bob Cranston (ca). 36 Alamy Images: Brandon Cole Marine Photography (cla); Reinhard Dirscherl (cb). Dive Gallery/Jeffrey Jeffords (www.divegallery.com): (bc). Image Quest Marine: Y. Kito (bl). 36–37 Alamy Images: Visual&Written SL/Takaji Ochi (c). 37 AguaSonic Acoustics: Mark Fischer (crb). Alamy Images: Sue Cunningham Photographic (cra); James Davis Photography (cr); Dinodia Images/ Ashvin Mehta (tr). Science Photo Library: (cb). 38–39 Corbis: Brenda Tharp. 42 Alamy Images: Danita Delimont (c). Corbis: Raymond Gehman (bc). DK Images: Harry Taylor (cra). 43 NASA: JPL (br). Science Photo Library: Bill Bachman (tr). 45 Corbis: Bettmann (tc); David Lawrence (cra). 46 Alamy Images: Norman Price (tr). Planetary Visions (bl). 46–47 Alamy Images: Nordicphotos/ Sigurgeir Sigurjonsson (b). 47 Planetary Visions (tr). 48 DK Images: Colin Keates/Courtesy of the Natural History Museum, London (tr). 49 Alamy Images: Douglas Peebles Photography (br). Woods Hole Oceanographic Instititution: Jayne Doucette (tr). 50–51 Getty Images: AFP/Lothar Slabon. 52–53 Corbis: Image by Digital image © 1996 CORBIS; Original image courtesy of NASA. NASA: Jesse Allen, Earth Observatory. Image interpretation provided by Dave Santek and Jeff Key, University of Wisconsin-Madison. 54 ESA: Eumetsat (cr). 55 Alamy Images: Kos Picture Source (t). DK Images: Peter Wilson (bl). 56 Action Images: Reuters/Carlo Borlenghi. 57 Alamy Images: Kos Picture Source (br). Corbis: Emmanuelle Thiercelin (cr). Getty Images: AFP/Marcel Mochet (tr); Clive Mason (cra). Rex Features: RAAF-AUSTRAL/ Corbis Sygma (crb). Clipper Round the World Yacht Race: Clipper Ventures Plc (cr). 58–59 NASA: Image courtesy the SeaWiFS Project, NASA/ Goddard Space Flight Center, and ORBIMAGE (c). 59 Alamy Images: Chris Linder (br). Corbis: Bettmann (tr). NASA: (cr); Image processed by Robert Simmon based on data from the SeaWiFS project and the Goddard DAAC (c). 60 SeaPics. com: Doug Perrine (bl). 61 S.M.R.U.: Simon Moss (bl). Courtesy of Andreas M. Thurnherr: (br). 62 Getty Images: Nordic Photos/Kristjan Fridriksson. 63 Alamy Images: Bryan & Cherry Alexander Photography (tr); Apex News and Pictures Agency/Tim Cuff (br). Corbis: Lowell Georgia (crb). FLPA: Minden Pictures/Flip Nicklen (c). 64 Alamy Images: Danita Delimont (bl). 65 Corbis: Bettmann (cla); Sygma/Gyori Antoine (bl). Getty Images: Photographer’s Choice/Kerrick James (tr). NASA: Image courtesy Jacques Descloitres, MODIS Land Rapid Response Team at NASA GSFC (clb). NOAA: Michael Van Woert, NOAA NESDIS, ORA (br). NASA: LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC (clb). TopFoto.co.uk: RIA Novosti / Sergey Mamontov (bl). 66 Alamy Images: Aflo Foto Agency (tr); Boating Images Photo Library/ Keith Pritchard (cra); Michael J. Kronmal (br); Tribaleye Images/J Marshall (bl). Corbis: Image by Digital image © 1996 CORBIS; Original image courtesy of NASA (clb). 67 Alamy Images: Mark Lewis (b); PHOTOTAKE Inc./Dennis Kunkel (tc). Getty Images: Photographer’s Choice/Malcolm Fife (tr). Courtesy of US Navy: Photo courtesy of Ian R. MacDonald, Texas A&M Univ. Corpus Christi (cla). 68 Alamy Images: Bill Brooks (cb); Images&Stories (br). Courtesy of Chris Baisan, University of Arizona: (bl). NASA: JPL (cl). NASA: JPL Ocean Surface Topography Team (cl, clb). 69 Corbis: Jonathan Blair (ca); EPA/Josue Fernandez (b). NOAA: Lieutenant Mark Boland, NOAA Corps (cla). Corbis: National Geographic Society / Robb Kendrick (c). Reuters: Reuters Photographer (b). 70 NASA: Image by Jesse Allen, NASA Earth Observatory; data provided by the MODIS Land Rapid Response Team, NASA GSFC (cl); Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC (cr); Jeff Schmaltz, MODIS Rapid Response Team, NASA/GSFC (c). NOAA: Aircraft Operations Center (br). NASA: Jeff Schmaltz, LANCE MODIS Rapid Response Team at NASA GSFC (cl); Lance Modis Rapid Response Team (c). NASA’s Earth Observatory: Jesse Allen (cr). 71 Corbis: EPA/Alejandro Ernesto (bl). OSF/ photolibrary: Warren Faidley (t). SeaPics.com: Doug Perrine (cr). Still Pictures: Michel Gunther (br). 72–73 Corbis: Reuters/Erik De Castro. 73 Corbis: Bryan Denton (crb); Demotix/Herman Lumanog (cra/Typhoon); EPA/Dennis M. Sabangan (cra/Typhoon Haiyan aftermath, cr, br); Reuters/ Erik De Castro (fcrb, crb/Food Drop). NASA: NASA Goddard MODIS Rapid Response Team (cb/Haiyan 8th Nov, cb/Haiyan 11th Nov). Planetary Visions Limited: (cra/Eye of the Storm). 74–75 Getty Images: Lonely Planet Images/Karl Lehmann. 76 Alamy Images: David Gregs (cr); ImagePix (bc).

iStockphoto.com: Dan Brandenburg (cra). NOAA: Captain Andy Chase (bl). OSF/photolibrary: Pacific Stock (crb). 77 Alamy Images: Michael Diggin (clb). Getty Images: Taxi/Helena Vallis (t). iStockphoto.com: Paul Topp (crb). 78 Alamy Images: Mooch Images (clb). 78–79 Getty Images: Robert Harding World Imagery/Lee Frost (b). 80 Alamy Images: Mary Evans Picture Library (br); Ian Simpson (bl). Don Dunbar (www. easternmaineimages.com): (tl) (c). 81 Alamy Images: Malcolm Fife (cb); Peter L. Hardy (bc). Still Pictures: Markus Dlouhy (tr). www.uwphoto.no: Erling Svensen (cl). 82 Alamy Images: Shaughn F. Clements (b); phototramp.com/Maciej Tomczak (cr). 83 Corbis: Dave Bartruff (l); Christie’s Images (br). 84–85 Corbis: Lawson Wood. 86–87 Getty Images: Photonica/Photolibrary.com. 88 Corbis: Yann Arthus-Bertrand (br). NASA: (clb). 89 Corbis: Michael Busselle (bc); Lloyd Cluff (t); Ecoscene/John Wilkinson (clb). DK Images: Colin Keates/Courtesy of the Natural History Museum, London (crb). 90 Rex Features: Sipa Press (SIPA). 91 Alamy Images: Louise Murray (br). Corbis: Matthieu Paley (c); Sygma/Kapoor Baldev (crb). Still Pictures: Bryan Lynas (tc); Mark Lynas (tr) (cr). 92 Alamy Images: Michael Howell (b). Corbis: Yann ArthusBertrand (cra); Jack Fields (c); Frans Lanting (tr). 93 Alamy Images: FLPA (clb); geogphotos (fcla). Corbis: Jim Sugar (bc). iStockphoto.com: Andrew Dorey (ca); Gregor Erdmann (cla). 94 Alamy Images: Jack Stephens (cl). Rob Havemeyer Acadia National Park ME: (tr). 94–95 Steven Russell (www.pbase.com/nodfather): (b). 95 Alamy Images: Eric Nathan (cr). Corbis: Kevin Fleming (tc). DK Images: Jon Spaull (tr). 96 Alamy Images: Atmosphere Picture Library/Bob Croxford (tr). Corbis: Ric Ergenbright (bl). DK Images: Rough Guides/Ian Aitken (crb). www. undiscoveredscotland.co.uk: (cla). 97 Alamy Images: Sean Burke (t); CuboImages srl/Marco Casiraghi (bl). NASA: Johnson Space Center - Earth Sciences and Image Analysis (br). 98 Corbis: Peter Johnson (c); Richard T. Nowitz (br). Wombat Pitts: (cra). 99 Alamy Images: Simon Reddy (cr). Getty Images: Robert Harding World Imagery/Neil Emmerson (b). Mark Kitching: (cl). NASA: Image courtesy Jacques Descloitres, MODIS Land Rapid Response Team at NASA GSFC (tc). 100–101 Corbis: Digital image © 1996 CORBIS; Original image courtesy of NASA. Andy Biggs. 102 Alamy Images: Danita Delimont (bc). Corbis: Bettmann (br). Still Pictures: Christoph Papsch (t). Dr Sandy Tudhope, Institute of Geology and Geophysics, Edinburgh University: (bl). 103 Alamy Images: Danita Delimont (b). Getty Images: Stone/James Randklev (cl). Marco Nero: (cr). 104 WaterLand Neeltje Jans: RWS MD afd. Multimedia. 105 Alamy Images: Florida Images (cr); geogphotos (cra); Rodger Tamblyn (tc). Corbis: Lowell Georgia (bl). Natural Visions: Heather Angel (c). NOAA: NOAA Restoration Center, Chris Doley (cb). Sky Pictures luchtfotografie (www.skypictures.nl): (br). 106 Alamy Images: Patrick Mallette (cl). Getty Images: Altrendo/altrendo nature (tr); Lonely Planet Images/Bethune Carmichael (clb). 106–107 Corbis: Martin Harvey (b). 107 Alamy Images: Guillen Photography (cra); Wildscape (c). DK Images: Shaen Adey (tr); James Stevenson (tl). 108 Alamy Images: Danita Delimont (tc); Peter Lewis (b). Paul Yung: (cr). 109 Alamy Images: Atmosphere Picture Library/ Bob Croxford (bl); imagebroker/Harald Theissen (cla). Corbis: Jason Hawkes (r). DK Images: Geoff Dann (br). 110 Alamy Images: Mark Boulton (tl). Corbis: Tony Arruza (bl);Yann Arthus-Bertrand (cr). 111 Alamy Images: Simon Reddy (tc); Laurie Wilson (b). Corbis: (cr). 112 Alamy Images: Ian Dagnall (tr); Danita Delimont (bc). Corbis: Douglas Peebles (br). DK Images: Lloyd Park (cl). 113 Alamy Images: Jon Arnold Images (crb). Corbis: Neil Rabinowitz (bl). Getty Images: National Geographic/Skip Brown (t). iStockphoto.com: Judi Ashlock (tr). 114 Corbis: Post-Houserstock/Dave G. Houser (cl). 114–115 Alamy Images: Jon Arnold Images/Doug Pearson (c). 115 Alamy Images: Tim Graham (ca). Corbis: (bc). DK Images: Dave King (tr). OSF/photolibrary: Richard Herrmann (cra). 116 Getty Images: Stone/Paul Souders (bl); Stone/ Tom Bean (cr). US Geological Survey: (bc). 116–117 Still Pictures: Guy Boily (t). 117 Corbis: Dale C. Spartas (bl). NASA: Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC (br). 118 Corbis: Reuters/Sergio Moraes (cr). NASA: Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC (b). Still Pictures: Jacques Jangoux (t). 119 Alamy Images: JL Images (tr). Corbis: Sygma/ Annebicque Bernard (bc). Courtesy of Clive Griffin (www.pbase.com/clivegriffin): (clb). Still Pictures: Christiane Eisler (cla). 120 Alamy Images: Jack Sullivan (cr). Pierre-Yves Lagrée, LMM

CNRS Université Paris VI: (t). NASA: Earth Sciences and Image Analysis Laboratory at Johnson Space Center (b). 121 Alamy Images: Karsten Wrobel (tr). Corbis: (clb);Yann Arthus-Bertrand (cla). DK Images: Rob Reichenfeld (crb). 122 Alamy Images: Eddie Gerald (b). Corbis: Carl & Ann Purcell (cr). NASA: Provided by the SeaWiFS Project, NASA/ Goddard Space Flight Center, and ORBIMAGE (tl); Imaginechina (bl). 123 Alamy Images: Tibor Bognar (cl). Corbis: Peter Guttman (br); Galen Rowell (b); Michael S.Yamashita (tr). 124 Alamy Images: Florida Images (crb); Renee Morris (bc). FLPA: Skylight (cl). 125 Corbis: James L. Amos (bc); Carol Havens (t). DK Images: Mike Linley (cr). Getty Images: Photographer’s Choice/Cameron Davidson (bl). Natural Visions: Heather Angel (br). 126 Alamy Images: Jon Sparks (t). Corbis: Rob Howard (bl). Still Pictures: Cal Vornberger (cr). 127 Alamy Images: David Poole (br); J. Schwanke (tr). Corbis: Annie Griffiths Belt (cla); Reuters/ Darren Staples (crb). 128 Alamy Images: Mark Boulton (cb); Rod Edwards (ca); Robert Harding Picture Library Ltd (br). 129 Corbis: Natalie Fobes (b); Steve Kaufman (br). Nial Moores/Birds Korea (www.birdskorea.org): (tc); Mr. Jeon Shi-Jin (cla). 130 Alamy Images: David Hosking (br). Getty Images: National Geographic/Tim Laman (tr). SeaPics.com: Jeremy Stafford-Deitsch (bc). 130–131 Oceanwide Images: Bob Halstead (c). 131 Alamy Images: Danita Delimont (cra); Reinhard Dirscherl (tr). Corbis: Michael S.Yamashita (br). SeaPics.com: D.R. Schrichte (ca). 132 DK Images: Rough Guides/Demetrio Carrasco (br); Peter Wilson (ca). 132–133 SeaPics.com: Masa Ushioda (t). 133 Alamy Images: Mireille Vautier (clb). Corbis: Stephen Frink (br). US Geological Survey: (cra). 134 Alamy Images: Tim Graham (bc). Corbis: (crb);Yann Arthus-Bertrand (ca). 135 Corbis: Arne Hodalic (cl). Getty Images: National Geographic/ Timothy Laman (tr). SeaPics.com: Jeremy StaffordDietsch (bc). Still Pictures: Alan Watson (br). 136–137 naturepl.com: Jurgen Freund. 138–139 naturepl.com: Aflo. Alamy Images: WaterFrame. 140 Alamy Images: Aqua Image (cla). DK Images: Frank Greenaway/Courtesy of the Natural History Museum, London (crb). iStockphoto.com: Ingvald Kaldhussæter (cra). Sue Scott: (bl). SeaPics.com: Mark Conlin (c). 141 British Marine Aggregate Producers Association (www.bmapa.org): (br). Getty Images: Image Bank/Astromujoff (t). OSF/ photolibrary: Michael Brooke (bc). 142 DK Images: Frank Greenaway/Courtesy of the Weymouth Sea Life Centre (bc); Jerry Young (cr). Sue Scott: (cl). SeaPics.com: Mark Conlin (bl). 142–143 David Hall (www.seaphotos.com): (c). 143 Image Quest Marine: Jim Greenfield (crb). Marine Wildlife: Paul Kay (tr). NOAA: Dr. James P. McVey, NOAA Sea Grant Program (bc). Sue Scott: (c). 144 DK Images: Frank Greenaway (ca). Sue Scott: (cl) (bl) (br). 144–145 Getty Images: National Geographic/Bill Curtsinger (t). 145 Alamy Images: Guillen Photography (bl). Sue Scott: (crb) (cra). 146 Alamy Images: Fabrice Bettex (bc); Gavin Parsons (cr). DK Images: Tim Ridley (tl). Marine Wildlife: Paul Kay (cla). Sue Scott: (clb). 147 Corbis: Ralph A. Clevenger (b). OSF/photolibrary: Tobias Bernhard (tc). Sue Scott: (cla) (cra). 148 Corbis: (tl). Sue Scott: (cra) (bl). SeaPics.com: Doug Perrine (crb). 149 Alamy Images: Mark Lewis (b); PNR Photography (crb). Dr. Alberto V. Borges/ Chemical Oceanography Unit from the University of Liège, Belgium: (tr). 150 Alamy Images: Ross Armstrong (tr); Joel Day (clb); Andre Seale (cla). Sue Scott: (bc). US Fish and Wildlife Service National Image Library: Chris Dau (br). 151 SeaPics.com: Phillip Colla. 152 Alamy Images: Danita Delimont (c); Nick Hanna (cl). Corbis: Yann Arthus-Bertrand (cr). 152–153 OSF/ photolibrary: Pacific Stock (c). 153 Dive Gallery/ Jeffrey Jeffords (www.divegallery.com): (tc). JM Roberts, Scottish Association for Marine Science: (crb). SeaPics.com: Clay Bryce (br); James D. Watt (cra). 154 Alamy Images: Michael Patrick O’Neill (bl); Sylvia Cordaiy Photo Library Ltd (tc). DK Images: Jerry Young (clb). 155 Alamy Images: Stephen Frink Collection (cra); Karen & Ian Stewart (c). Dive Gallery/Jeffrey Jeffords (www. divegallery.com): (br). SeaPics.com: Andrew J. Martinez (tl); James D. Watt (bl). 156 Alamy Images: Stephen Frink Collection (bl). Corbis: Stephen Frink (c); Lawson Wood (tc). 157 Corbis: Bob Krist (b). SeaPics.com: Rodger Klein (tr). 158 Alamy Images: Nick Hanna (tr); Martin Harvey (bl); Zute Lightfoot (br). 159 Alamy Images: Steve Allen Travel Photography (tr); Slick Shoots (cr). Corbis: Cordaiy Photo Library Ltd/John Parker (cla). SeaPics.com: Marc Bernardi (b). 160 Alamy Images: Aqua Image (cla). SeaPics.com: James D. Watt (b). Still Pictures: Lynn Funkhouser (cra). 161

ACKNOWLEDGMENTS Alamy Images: Robert Harding Picture Library Ltd (crb); Andre Seale (clb). Corbis: Reuters/Handout (cra). Brian McMorrow: (tr). SeaPics.com: James D. Watt (br). 162–163 Oceanwide Images: Gary Bell. 164 DK Images: Frank Greenaway (clb). NASA: Image and animations provided by the SeaWiFS Project and the NASA GSFC Scientific Visualization Studio (cra). Sue Scott: (tl) (bc) (br). 165 Alamy Images: Jeremy Inglis (br); Andre Seale (bl). Image Quest Marine: Scott Tuason (t). 166–167 Getty Images: Stone/Kim Westerskov. 168 Science Photo Library: Alexis Rosenfeld (bc). 169 DeepSeaPhotography.Com: Kim Westerskov (tc). Image Quest Marine: Peter Parks (br). Science Photo Library: Susumu Nishinaga (cb). SeaPics.com: Ingrid Visser (c). 170 OSF/ photolibrary: (cla); Howard Hall (b). SeaPics.com: Peter Parks/iq3-d (tc). 171 ExploreTheAbyss.Com: Peter Batson (cr) (clb) (bl) (br). Image Quest Marine: Peter Herring (tr). NOAA: Archival Photography by Steve Nicklas, NOS, NGS (c). OSF/ photolibrary: Pacific Stock (tc). 172 Getty Images: National Geographic/Paul Nicklen. 173 Alamy Images: epa european pressphoto agency b.v. (br). DeepFlight: (cra/Deepflight Super Falcon). NOAA: (cr, crb). www.uboatworx.com: David Pearlman (fcra). 174 Science Photo Library: (tr). 175 DeepSeaPhotography.Com: Kim Westerskov (br). NOAA: Image Courtesy of the Deep Atlantic Stepping Stones Science Party, IFE , URI-IAO, and NOAA (bc); Office of Ocean Exploration (cb). Science Photo Library: Dr Ken MacDonald (t). SeaPics.com: Mark Conlin (bl). 176 NOAA: Commander John Bortniak, NOAA Corps (bl); Fisheries Collection (br). Dr. P. J. Ramsay/African Coelacanth EcoSystem Programme: (cl). 177 Alamy Images: Ron Scott (br). ExploreTheAbyss. Com: Peter Batson (bc). NASA: Image provided by the USGS EROS Data Center Satellite Systems Branch (tr). NOAA: OAR/National Undersea Research Program (NURP); University of Connecticut (ca); Ocean Explorer (cb). 178 www. uwphoto.no: Erling Svensen. 179 ExploreTheAbyss.Com: Peter Batson (cra). FLPA: D. P. Wilson (c). Jason Hall-Spencer/Marine Conservation Society: (crb). JM Roberts, Scottish Association for Marine Science: (bc); AWI & Ifremer 2003 (tc) (br). 180 Alamy Images: Travelpix (clb). NASA: Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC (br). NOAA: National Geophysical Data Center (cla). SeaPics. com: David Wrobel (bl). 181 Alamy Images: Phototake Inc./Dennis Kunkel (bc). Image Quest Marine: Peter Parks (t). Science Photo Library: Steve Gschmeissner (cb). SeaPics.com: D.R. Schrichte (br). 182 Alamy Images: Blickwinkel (clb). ExploreTheAbyss.Com: Peter Batson (cla). SeaPics.com: Doug Perrine (bl). Craig Smith & Mike Degruy: (br). 182–183 NOAA: OAR/ National Undersea Research Program (NURP) (c). 183 naturepl.com: David Shale (bl). Naval Historical Foundation, Washington, D.C.: (br). Science Photo Library: US Geological Survey (tr). 184 Alamy Images: Fabrice Bettex (tr). Corbis: The Oregonian/Doug Beghtel (bl). 184–185 Corbis: Yann Arthus-Bertrand (b). 185 Alamy Images: David Tipling (c). Corbis: Cordaiy Photo Library Ltd/John Farmar (ca); Ralph White (tl). Planetary Visions: Lamont-Doherty Earth Observatory (br). 186 Planetary Visions. 187 European Space Agency: Denmann Production (clb). NASA: Canadian Space Agency/National Snow and Ice Data Centre (crb); GSFC (tr) (ca) (cra); JPL (c); JPLCaltech (cb). Science Photo Library: David Vaughan (br). University College London: (cb). 188 Image courtesy of Karen L. Von Damm. Image obtained from the DSV Alvin, with funding provided by the U.S. National Science Foundation: (tr). Science Photo Library: Southampton Oceanography Centre/B. Murton (bl). 188–189 Woods Hole Oceanographic Instititution: (c). 189 ExploreTheAbyss.Com: Peter Batson (tc) (c) (br). Richard T. Lutz: (cr). NOAA: Ocean Explorer (bl). 190–191 FLPA: Minden Pictures/Norbert Wu. 192 Bridgeman Art Library: Royal Geographical Society, London, UK (tr). Corbis: Ecoscene/Graham Neden (cb). 193 Alamy Images: Rosemary Calvert (b); John Digby (tl). SeaPics.com: Franco Banfi (tr). 194 Alamy Images: Blickwinkel (br); Eric Ghost (fbr); K-Photos (tc). M.A. Felton: (bc). NOAA: Michael Van Woert, NOAA NESDIS, ORA (crb). 194–195 Getty Images: Photographer’s Choice/Siegfried Layda (c). 195 Alamy Images: Giles Angel (crb); Nordicphotos/Kristjan Fridriksson (tr). 196 Corbis: Sygma. Science Photo Library: NOAA. 197 Corbis: Bettmann (ca) (cra); Hulton-Deutsch Collection (tr); Ralph White (crb) (cb) (br). Henning Pfeifer: (clb). Rex Features: ITV (ITV/TPC) (c). Science Photo Library: NOAA. 198 Alamy Images: Bryan & Cherry Alexander Photography (fbl) (br). NOAA: Michael Van Woert, NOAA NESDIS, ORA (bl). Courtesy of Don Perovich: (fbr). 198–199 Bryan and Cherry Alexander Photography: (t). 199 Corbis: Bettmann (cra). DK Images: Harry Taylor (crb). NOAA: Michael Van Woert, NOAA NESDIS, ORA (bc) (br). SeaPics. com: John KB Ford/Ursus (c). 200 NASA: Jacques

Descloitres, MODIS Land Rapid Response Team, NASA/GSFC (cl). 200–201 Alamy Images: Brandon Cole Marine Photography (b). 201 Alamy Images: Popperfoto (br). Corbis: Paul A. Souders (tc). SeaPics.com: Bryan & Cherry Alexander (c); iq3-d/Peter Parks (cra). 202–203 Getty Images: Image Bank/Mike Kelly. 204–205 DeepSeaPhotography.Com: Kim Westerskov. 206 Alamy Images: Bruce Coleman/Tom Brakefield (cl/Kingdom); Norma Jospeh (c);Visual&Written SL/ Kike Calvo (cl/Genus). Corbis: Brandon D. Cole (b/ Hagfish). DK Images: (cl/Domain); Martin Camm (cl/Phyllum) (cl/Order) (cl/Family) (cl/Species); Geoff Dann (b/Lamprey) (b/Ray-Finned Fish); Frank Greenaway (b/Cartilaginous Fish); David Peart (cl/ Class). SeaPics.com: Mark V. Erdmann (b/LobeFinned Fish). 207 DK Images: (Fungi); Neil Fletcher (Plants); Dave King (Red Seaweeds); Jane Miller (Animals); Karl Shone (Brown Seaweeds). SeaPics. com: iq3-d/Peter Parks (Protists). 208 DK Images: (Echinoderms); Frank Greenaway (Mollusks); Dave King (Arthropods). 209 DK Images: Jerry Young (Chordates). 210 FLPA: Minden Pictures/Chris Newbert. 211 Conservation International: Robert Thacker (ca); Jeffrey T. Williams/Smithsonian Institution (c). FLPA: Minden Pictures/Norbert Wu (crb). Dr J. Frederick Grassle, Rutgers University: (br). Sue Scott: (tr) (cra). SeaPics.com: Phillip Colla (cb). 212 Still Pictures: Steven Kazlowski (crb). 213 iStockphoto.com: Dan Schmitt (cla). SeaPics.com: Doug Perrine (b). Still Pictures: Bob Evans (tc). 214 DeepSeaPhotography.Com: Kim Westerskov (clb). FLPA: D. P. Wilson (cla). OSF/photolibrary: Mark Jones (br). Sue Scott: (cra) (cr) (bc). 215 M. Boyer/edge-ofreef.com: (bc). OSF/photolibrary: Richard Herrmann (t). SeaPics.com: Masa Ushioda (br). 216 iStockphoto.com: Dan Schmitt (bl). Sue Scott: (tr) (cl) (ca). 216–217 SeaPics.com: Espen Rekdal (b). 217 Dive Gallery/Jeffrey Jeffords (www. divegallery.com): (br). Marine Wildlife: Paul Kay (ca) (cr). Sue Scott: (tr). 218 FLPA: Linda Lewis (cra). Still Pictures: Secret Sea Visions (br); Gunter Ziesler (bl). 218–219 FLPA: Minden Pictures/ Norbert Wu (c). 219 Alamy Images: Danita Delimont (bl). 220 Alamy Images: SCPhotos/Tom & Pat Leeson (bl); Bruce Coleman/Patrice Ricard (fbr). iStockphoto.com: Steffen Foerster (cl). SeaPics.com: Mark Conlin (cra) (clb); Chris Huss (fbl) (br). 221 Getty Images: National Geographic/ Brian J. Skerry (t). OSF/photolibrary: Doug Allan (bl). 222 Alamy Images: Brandon Cole Marine Photography (bc). FLPA: Minden Pictures/Norbert Wu (c). 223 ExploreTheAbyss.Com: Peter Batson (ca) (bl). Charles G. Messing/Nova Southeastern University, Florida: (br). NOAA: OAR/National Undersea Research Program (NURP); Univ. of Hawaii (cra). OSF/photolibrary: Norbert Wu (cla). 224 DK Images: (bl). Image Quest Marine: (c);Y. Kito (br). 224–225 ExploreTheAbyss.Com: Peter Batson (t). 225 ExploreTheAbyss.Com: Peter Batson (cl). OSF/photolibrary: (br). SeaPics.com: iq3d/Peter Parks (cr). 226 DK Images: Colin Keates (bl/above) (bl). Science Photo Library: Ria Novosti (cra); Sinclair Stammers (cl). 226–227 FLPA: Minden Pictures/Fred Bavendam (b). 227 The Academy of Natural Sciences: Ted Daeschler (cl). DK Images: Colin Keates (cla) (tr) (cra); Harry Taylor/Courtesy of the Royal Museum of Scotland, Edinburgh (c). SeaPics.com: Doug Perrine (tl). 228 Alamy Images: Natural Visions/Heather Angel (tc). Bridgeman Art Library: Private Collection (cra). DK Images: Harry Taylor/Courtesy of the Hunterian Museum (University of Glasgow) (c); Harry Taylor/Courtesy of the Natural History Museum, London (bc). OSF/photolibrary: Karen Gowlett-Holmes (br). Science Photo Library: David Parker (clb). 229 Alamy Images: David Fleetham (tc); Stephen Frink Collection/James D. Watt (cra). DK Images: (c/Terrestrial Mammal) (c/ Jawless Fish); Bedrock Studios (c/Armored Fish) (c/ Turtle); Robin Carter (c/Placodont); Neil Fletcher (c/ Penguin); Giuliano Fornari (c/Ichthyosaurus) (c/ Plesiosaur); Jon Hughes (c/Whale); Colin Keates (bl) (c/Cambrian) (c/Ediacaran) (c/Ammonite); Harry Taylor/Courtesy of the Natural History Museum, London (c/Shark); Harry Taylor/Courtesy of the Royal Museum of Scotland, Edinburgh (c/LobeFinned). Getty Images: Science Faction/G. Brad Lewis (br). 230–231 Getty Images: Taxi/Gary Bell. 232 MicroScope/Woods Hole: D. J. Patterson (cb). NOAA: OAR/National Undersea Research Program (NURP); Lousiana Univ. Marine Consortium (cr). Oceanwide Images: Gary Bell (b). OSF/ photolibrary: Phototake Inc/Dennis Kunkel (ca). University of Illinois at Urbana-Champaign: (cra). 233 DK Images: M.I. Walker (tc). Image Quest Marine: Peter Parks (cl). Oceanwide Images: Rudie Kuiter (bc). Still Pictures: Tom E. Adams (cr). Laura K. Sycuro, Fred Hutchinson Cancer Research Center, Seattle: (bl). 234-235 Science Photo Library: Mint Images/Frans Lanting (c). 238 Algaebase.org: M.D. Guiry (cr) (br); John Huisman (cl). Sue Scott: (bl). 239 Alamy Images: Bob Gibbons (t). Algaebase.org: M.D. Guiry (bl). Natural Visions: Heather Angel (br). Sue Scott: (cr). 240–241 Corbis: Ralph A. Clevenger. SuperStock: National Geographic/Mauricio

Handler. 242 Sue Scott: (cra). 242–243 Image Quest Marine: Roger Steene (c). 243 Rob Houston: (bc). Sue Scott: (tc) (cr). 244 naturepl. com: Sue Daly (cr). 246 Algaebase.org: Ignacio Bárbara (cra); Coastal Imageworks/Colin Bates (bc); M.D. Guiry (tr). Sue Scott: (cl) (cr) (br). 247 Alamy Images: Olivier Digoit (cra); Sami Sarkis (br); Kevin Schafer (tl). Algaebase.org: John Huisman (clb). SeaPics.com: Andrew J. Martinez (crb). 248 Natural Visions: Heather Angel (cra) (bc). Charles J. OKelly: (tc). Science Photo Library: Alexis Rosenfeld (c). 249 Natural Visions: Heather Angel (cl). Jonathan Sleath: (bl) (crb); Dr David Holyoak (cra). 250 Alamy Images: Andrew Woodley (cl). Sue Scott: (bl) (cr) (br). SeaPics.com: Jeremy StaffordDeitsch (ca). 251 Alamy Images: Nature Picture Library/Jose B. Ruiz (cl); Wildscape/Jason Smalley (cr). Sue Scott: (cla) (b). 252 Alamy Images: Roger Eritja (tr); Marilyn Shenton (tl). OSF/photolibrary: Kathie Atkinson (br). Sue Scott: (bl). US Geological Survey: Forest & Kim Starr (cl). 253 Corbis: FLPA/Peter Reynolds (tc). DK Images: Richard Watson (bl). FLPA: Minden Pictures/Tui De Roy (tl). OSF/photolibrary: (br). 254 Getty Images: Lonely Planet Images/Grant Dixon (r). MicroScope/Woods Hole: David Patterson, Linda Amaral Zettler, Mike Peglar and Tom Nerad (fcl). Natural Visions: Heather Angel (bc). OSF/ photolibrary: Phototake Inc. (cl). 255 MicroScope/ Woods Hole: David Patterson & Aimlee Laderman (br). Einar Timdal/University of Oslo: (cl) (tr) (cb) (bl). 256 Alamy Images: Brandon Cole Marine Photography (cr); Robert Fried (cla). FLPA: Minden Pictures/Fred Bavendam (bc). Andy Murch/ Elasmodiver.com: (br). OSF/photolibrary: (clb). SeaPics.com: Mark Conlin (crb); Doug Perrine (tr). 257 Alamy Images: Dave and Sigrun Tollerton (cla). FLPA: Minden Pictures/Birgitte Wilms (b). SeaPics. com: Phillip Colla (tc). 258 Alamy Images: Andre Seale (cr). Dr. Frances Dipper: (fcl) (cl) (br). Natural Resources Canda: The Sponge Reef Project (clb). 259 Alamy Images: Wolfgang Pölzer (bl). Dr. Frances Dipper: (tr) (ca) (cb). Keith Hiscock: (tl). Prof. Dr. Joachim Reitner/ Universität Göttingen: (br). Dreamstime.com: Nanisub (c). 260 Alamy Images: Tribaleye Images/J. Marshall (cra). OSF/photolibrary: Pacific Stock/ David Fleetham (bl). SeaPics.com: Mark Conlin (c); Doug Perrine (cla). 260–261 Getty Images: National Geographic/Paul Nicklen (b). 261 Dr. Frances Dipper: (bc). DK Images: Frank Greenaway (cla). OSF/photolibrary: (cr). SeaPics. com: David Wrobel (ca). 262 Alamy Images: Reinhard Dirscherl (crb). Dr. Frances Dipper: (cb). Sue Scott: (bl). SeaPics.com: iq3-d/Chris Parks (t); David Wrobel (bc). 263 Richard L. Lord. 264 Marine Wildlife: Paul Kay (br). SeaPics.com: Jeremy Stafford-Deitsch (cl); Steven Wolper (bc). Still Pictures: Kelvin Aitken (ca). 265 Alamy Images: Andre Seale (clb). Dr. Frances Dipper: (br). NOAA: Mr. Mohammed Al Momany, Aqaba, Jordan (t). SeaPics.com: Doug Perrine (bc). 266 Alamy Images: Michael Patrick O’Neill (cr) (bl); Wolfgang Pölzer (tc). Sue Scott: (c) (crb). 267 Sue Scott: (cl) (tc) (c) (br). SeaPics.com: Franco Banfi (cr). 268 Alamy Images: Aqua Image (cl). OSF/ photolibrary: Tobias Bernhard (b). SeaPics.com: Masa Ushioda (cra). Dr. Charlie Veron/Australian Institute of Marine Science: Photo by Mary Stafford-Smith (c). 269 Alamy Images: Mark Morgan (cl). Dr. Frances Dipper: (crb). Marine Wildlife: Paul Kay (clb). SeaPics.com: Doug Perrine (tr). NOAA: Lophelia II 2012 Expedition, NOAA-OER/BOEM (br). 270 Alamy Images: Nature Picture Library/Jose B. Ruiz (b). Dr. Frances Dipper: (ca). Sue Scott: (t). SeaPics.com: Doug Perrine (cr). 271 Alamy Images: FLPA (c). M. Boyer/edge-of-reef.com: (cr) (bl). OSF/ photolibrary: Tobias Bernhard (tr). Sue Scott: (br). 272 M. Boyer/edge-of-reef.com: (cl) (cla) (bl). Courtesy of John J. Holleman: (crb). Michael D. Miller: (tr) (cr). 273 Image Quest Marine: Peter Parks (cr); Roger Steene (cl). Marine Wildlife: Paul Kay (bl). Kåre Telnes/Seawater.no: (br). 274 Corbis: Lawson Wood (tr). Keith Hiscock: (cb). Image Quest Marine: Roger Steene (ca). Marine Wildlife: Paul Kay (crb). SeaPics.com: Larry Madrigal (cra). 275 Dive Gallery/Jeffrey Jeffords (www.divegallery.com): (c). DK Images: Steve Gorton (cla). ExploreTheAbyss.Com: Peter Batson (br). Dr. Dieter Fiege: (tc) (cra). Image Quest Marine: Jim Greenfield (bl). 276 DK Images: Matthew Ward (c) (clb). SeaPics.com: Clay Bryce (ca). 276–277 Getty Images: Image Bank/Mike Severns (c). 277 Alamy Images: Robert Harding Picture Library Ltd/Sylvain Grandadam (tr). Dive Gallery/Jeffrey Jeffords (www.divegallery.com): (cr) (br). DK Images: Andreas Von Einsiedel (cra). OSF/photolibrary: Karen Gowlett-Holmes (cla) (ca). SeaPics.com: Doc White (c). 278 Alamy Images: Daniel L. Geiger/SNAP (tc); Wildscape/ Jason Smalley (tr). SeaPics.com: Mark Strickland (b). 279 Alamy Images: Nature Picture Library/Jose B. Ruiz (ca). Keith Hiscock: (tr). Image Quest Marine: Peter Parks (cra); Scott Tuason (cr). SeaPics. com: John C. Lewis (tl). Alamy Images: age fotostock (cla). 280 Marine Wildlife: Paul Kay (t). SeaPics.com: Marilyn & Maris Kazmers (bc); Espen

Rekdal (cl). 281 DK Images: Andreas von Einsiedel (ca). FLPA: Minden Pictures/AUSCA/D. Parer & E. Parer-Cook (crb). Jon Moore/Coastal Assessment Liaison & Monitoring, Pembroke: (tl). SeaPics. com: D. R. Schrichte (b). 282–283 Getty Images: Taxi/Pete Atkinson. 284 Alamy Images: Natural Visions/Heather Angel (cl). DK Images: Dave King (tc); Frank Greenaway/Courtesy of the Natural History Museum, London (bc). FLPA: Minden Pictures/Norbert Wu (cra). Image Quest Marine: Roger Steene (crb) (br). Alamy Images: Juniors Bildarchiv GmbH (bc). 285 Alamy Images: LiquidLight Underwater Photography (br). Oceanwide Images: Gary Bell (t). SeaPics.com: James D. Watt (clb). 286 Alamy Images: Carol Buchanan (tl). Dive Gallery/Jeffrey Jeffords (www.divegallery.com): (c). Marine Wildlife: Lucy Kay (cra). NOAA: National Estuarine Research Reserve Collection (br). 287 Alamy Images: Andre Seale (br). FLPA: Minden Pictures/Norbert Wu (t). 288 Corbis: Jeffrey L. Rotman (b). Image Quest Marine: Peter Batson (ca). Oceanwide Images: Gary Bell (cra). SeaPics. com: Doug Perrine (tl); Jeff Rotman (crb). 289 Alamy Images: f1 online (bl). Image Quest Marine: Peter Batson (bc). Oceanwide Images: Gary Bell (t). SeaPics.com: Marc Chamberlain (br). 290 Alamy Images: Daniel L. Geiger/SNAP (cla). DK Images: Colin Keates/Courtesy of the Natural History Museum, London (cra). NHPA: Ken Griffiths (bl). OSF/photolibrary: Barrie Watts (clb). SeaPics.com: Espen Rekdal (tr). 291 Dive Gallery/Jeffrey Jeffords (www.divegallery.com): (b). Image Quest Marine: Jez Tryner (cla) (ca) (cra). NOAA: Jamie Hall (tr). 292 DK Images: Frank Greenaway/Courtesy of the Natural History Museum, London (cra). Image Quest Marine: Roger Steene (tl). naturepl.com: Christophe Courteau (cl). NOAA: Dr. Bradley Stevens (crb). Still Pictures: Fred Bavendam (tr). 293 FLPA: Minden Pictures/Fred Bavendam (r). NOAA: Hopcroft (bl). SeaPics.com: Franco Banfi (cl). 294 Photo Biopix.dk: (bl). iStockphoto.com: Ian Campbell (br). SeaPics.com: Marli Wakeling (tr). 295 Dive Gallery/Jeffrey Jeffords (www. divegallery.com): (cr). Ifremer (www.ifremer.fr): A. Le Magueresse (clb). Natural Visions: Heather Angel (cl). Still Pictures: Everson (br). 296 Dive Gallery/Jeffrey Jeffords (www.divegallery.com): (b). DK Images: Frank Greenaway (cr). OSF/ photolibrary: (cl). Still Pictures: Lynda Richardson (tr). 297 DK Images: Jane Burton (c); Andreas von Einsiedel (bc); Dave King (cra). Image Quest Marine: Masa Ushioda (crb). David Kusner: (tc). OSF/photolibrary: Green Cape Pty Ltd (bl). 298–299 Steve Smithson. 300 DK Images: Jane Burton (bl). Marine Wildlife: Paul Kay (cl) (br). SeaPics.com: Masa Ushioda (cr). 301 Alamy Images: Maximilian Weinzierl (tr). DK Images: Kim Taylor & Jane Burton (cr). Oceanwide Images: Gary Bell (tl). SeaPics.com: David B. Fleetham (b). 302 naturepl.com: Jurgen Freund. 303 Corbis: Roger Garwood & Trish Ainslie (tr). SeaPics.com: Ralf Kiefner (c) (crb). 304 Laurent Dabouineau/University U.C.O. Bretagne Nord, France: (cl). FLPA: Foto Natura/Jef Meul (ca). Nature Portfolio (www.natureportfolio.co.uk): Bob Ford (br). 305 Alamy Images: SNAP/Daniel L. Geiger (cl). Karen Gowlett-Holmes: (crb). Marine Wildlife: Lucy Kay (cra). Sue Scott: (bl) (bc). Kåre Telnes/Seawater.no: (tr). 306 SeaPics. com: Phillip Colla (cl). 306–307 Getty Images: Lonely Planet Images/Michael Aw (c). 307 Alamy Images: David Fleetham (tr). Corbis: FLPA/ Douglas P. Wilson (tc). Sue Scott: (br). SeaPics. com: Marli Wakeling (bl). Still Pictures: P. Danna (cr). 308 Alamy Images: David Fleetham (clb). M. Boyer/edge-of-reef.com: (tr). Marine Wildlife: Paul Kay (crb). Oceanwide Images: Gary Bell (br). Sue Scott: (cla). SeaPics.com: D.R. Schrichte (bl). 309 Dive Gallery/Jeffrey Jeffords (www. divegallery.com): (t). OSF/photolibrary: Tobias Bernhard (bl). Sue Scott: (br). 310 M. Boyer/ edge-of-reef.com: (tr) (cl). Marine Wildlife: Paul Kay (cr). SeaPics.com: David Wrobel (bl). 311 Dr. Frances Dipper: (bl). DK Images: Frank Greenaway (cl); Colin Keates (cr). Richard Ling: (crb). Charles G. Messing/Nova Southeastern University, Florida: (tr). 312 Alamy Images: F. Jack Jackson (clb). Australian Institute of Marine Science: (t). Dr. Jacob Dafni: Dr. A. Diamant (bc). Image Quest Marine: Peter Herring (br); Roger Steene (cra). Corbis: Visuals Unlimited / David Wrobel (br). 313 Alamy Images: Lawrence Stepanowicz (cra). ExploreTheAbyss.Com: Peter Batson (br). OSF/photolibrary: Stephen Foote (bl). SeaPics.com: Andrew J. Martinez (cl). Peter Funch, University of Aarhus: (crb). Science Photo Library: Andrew J. Martinez (br). 314 Corbis: Lawson Wood (clb). FLPA: D. P. Wilson (c). www.uwphoto.no: Erling Svensen (tl) (cra) (br). 315 ExploreTheAbyss.Com: Peter Batson (ca). NOAA: OAR/National Undersea Research Program (NURP); College of William & Mary (tr). SeaPics.com: Scott Leslie (b). Getty Images: Visuals Unlimited / Richard Herrmann (tr). 316 FLPA: Foto Natura/Jan Van Arkel (t). Peter Funch, University of Aarhus: (bl). M. Antonio Todaro, University of Modena e Reggio Emilia: (br).

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ACKNOWLEDGMENTS FLPA: Minden/FN/Jan Van Arkel (cla). 317 Alamy Images: David Fleetham (br). M. Boyer/edge-ofreef.com: (c). ExploreTheAbyss.Com: Peter Batson (tr). Image Quest Marine: Peter Parks (tc). Lyubomir Klissurov: (bl). Still Pictures: Roland Birke (cla). 318 M. Boyer/edge-of-reef.com: (c). ExploreTheAbyss.Com: Peter Batson (cl). Sue Scott: (bc). SeaPics.com: Espen Rekdal (br). 319 M. Boyer/edge-of-reef.com: (cla). Dr. Frances Dipper: (cra). Photo by Per R. Flood © Bathybiologica.no: (bc). Natural Visions: Heather Angel (br). Sue Scott: (ca). SeaPics.com: David Wrobel (clb). 320 Corbis: Brandon D. Cole (crb). ExploreTheAbyss.Com: Peter Batson (tr) (bl). SeaPics.com: Jonathan Bird (br). 321 Corbis: Brandon D. Cole (crb). OSF/photolibrary: (tr); Zig Leszcynski (cla). www.uwphoto.no: Erling Svensen (bl). 322 Alamy Images: Brandon Cole Marine Photography (cra). DK Images: Frank Greenaway (cl); James Stevenson (ca). 322–323 Corbis: Denis Scott (b). 323 DK Images: Frank Greenaway (br); Dave King (tc). SeaPics.com: Doug Perrine (cl) (bc). 324 Janna Nichols: (clb). SeaPics.com: Doug Perrine (tl) (ca). www.uwphoto.no: Erling Svensen (br). 325 Andy Murch/Elasmodiver.com: (cra). OSF/photolibrary: Paul Kay (bl). Still Pictures: Kelvin Aitken (cla) (crb). 326 Alamy Images: Stephen Frink Collection/Marty Snyderman (br). OSF/photolibrary: Gerard Soury (bl). SeaPics. com: Saul Gonor (cra); Espen Rekdal (cla). 327 Alan Chow: (bc). Dr. Frances Dipper: (br). DK Images: Frank Greenaway (bl). Andy Murch/ Elasmodiver.com: (t). 328 Andy Murch/ Elasmodiver.com: (t) (br) (bc). naturepl.com: Bruce Rasner/Jeff Rotman (cl). 329 Alamy Images: Jeff Rotman (cla). DK Images: Harry Taylor/ Courtesy of the Natural History Museum, London (cl). John A. Scarlett: (tr). SeaPics.com: Scott Michael (br); David Shen (clb). 330–331 Steve Bloom Images. OceanwideImages.com: C & M Fallows. 332 OSF/photolibrary: Pacific Stock (br). Powder River Photography/Todd Mintz: (cl). SeaPics.com: Richard Herrmann (tl). 333 Alamy Images: David Fleetham (br); Michael Patrick O’Neill (tl). DK Images: Frank Greenaway (bc). naturepl.com: Jeff Rotman (cr). SeaPics.com: Doug Perrine (crb). 334 Andy Murch/ Elasmodiver.com: (br). SeaPics.com: Randy Morse (cl). 334–335 Marine Wildlife: Alexander Mustard (t). 335 Alamy Images: M. Timothy O’Keefe (c). Image Quest Marine: Carlos Villoch (br). SeaPics.com: Doug Perrine (clb); Tim Rock (br). 336 Alamy Images: WorldFoto (cra). DK Images: Colin Keates/Courtesy of the Natural History Museum, London (clb). 336–337 Alamy Images: Reinhard Dirscherl (c). 337 Alamy Images: Mark Boulton (br). Dive Gallery/Jeffrey Jeffords (www.divegallery.com): (cb). OSF/ photolibrary: David Fleetham (tr). 338 Alamy Images: Reinhard Dirscherl (bl); Stephen Frink Collection (cl); Images&Stories (tr). DK Images: Frank Greenaway (cla). Naoko Kouchi: (cla/ Background). SeaPics.com: Doug Perrine (br). 339 Alamy Images: Blickwinkel (bc). FLPA: Minden Pictures/Fred Bavendam (cl). OSF/photolibrary: Dr. F. Ehrenstrom & L. Beyer (ca) (crb). 340 DK Images: Steve Gorton (clb); Colin Keates/Courtesy of the Natural History Museum, London (tc). Getty Images: Taxi/Peter Scoones (cl). Image Quest Marine: Masa Ushioda (crb). SeaPics.com: Mark V. Erdmann (cr). Andreas Svensson/Norwegian University of Science and Technology: (bl). 341 Marine Wildlife: Alexander Mustard (t). Robert A. Patzner, University of Salzburg, Austria: (br). 342 Ardea: Pat Morris (cb). Rick J. Coleman: (bl). DK Images: (cla). Marine Wildlife: Alexander Mustard (tr). Dr. Volker Neumann: (br). 343 DK Images: (clb). FLPA: Minden Pictures/Norbert Wu (crb). Marine Wildlife: Alexander Mustard (t). 344 Corbis: Paul A. Souders (bl). OSF/photolibrary: Sue Scott (tl). SeaPics.com: Mark Conlin (c); Jeff Jaskolski (br). 345 Alamy Images: FLPA/S. Jonasson (bl); Andre Seale (tl). SeaPics.com: Shedd Aquar/ Ceisel (cr). 346 Alamy Images: Wolfgang Pölzer (b). Getty Images: National Geographic/Paul Nicklen (t). 347 FLPA: Minden Pictures/Norbert Wu (cla). Getty Images: National Geographic/Wolcott Henry (bc). Image Quest Marine: Peter Herring (tr). OSF/photolibrary: Paulo De Oliveira (bl). 348 DK Images: Frank Greenaway (cr). Keith Hiscock: (cra). OSF/photolibrary: Doug Allan (b). SeaPics. com: Hideyuki Utsunomiya (ca). 349 Peter Ajtai: (clb). SeaPics.com: Marilyn & Maris Kazmers (br). www.uwphoto.no: Erling Svensen (cla) (tc). 350 Image Quest Marine: Peter Herring (t); Justin Marshall (br). SeaPics.com: James D. Watt (clb). 351 FLPA: Minden Pictures/Norbert Wu (cr). marinethemes.com: Kelvin Aitken (tc). Natural Visions: Peter David (clb). OSF/photolibrary: Neil Bromhall (br); Rodger Jackman (ca). FLPA: Biosphoto/Bruno Guenard (clb). 352 Dr. Frances Dipper: (clb). FLPA: D. P. Wilson (cla). Oceanwide Images: Gary Bell (bc); Rudie Kuiter (crb). OSF/ photolibrary: Richard Herrmann (tr). Alamy Images: WaterFrame (ca). 353 DK Images: Dave King (br). FLPA: Minden Pictures/Norbert Wu (l). New Zealand Seafood Industry Council Ltd: (cr). 354 Magnum Photos: Harry Gruyaert . 355

Alamy Images: Charles Bowman (bl); Jeff Rotman (crb). FLPA: Minden Pictures/Norbert Wu (ca). naturepl.com: Michael Pitts (cr). OSF/ photolibrary: Sue Scott (cb). Sue Scott: (cra). SeaPics.com: Richard Herrmann (br). 356 Dive Gallery/Jeffrey Jeffords (www.divegallery.com): (br). NHPA: A.N.T. Photo Library (t). Robert A. Patzner, University of Salzburg, Austria: (cb). 357 Alamy Images: Papilio/Steve Jones (crb); Wolfgang Pölzer (tl). Dive Gallery/Jeffrey Jeffords (www.divegallery.com): (cl) (bl). 358 Alamy Images: Blickwinkel (cr); Reinhard Dirscherl (b). Marine Wildlife: Paul Kay (cla). SeaPics.com: Doug Perrine (cl). 359 Dr. Frances Dipper: (bc). DK Images: Jerry Young (tr). OSF/photolibrary: David Fleetham (tl); Pacific Stock (crb). Robert A. Patzner, University of Salzburg, Austria: (clb). SeaPics.com: V&W/Hal Beral (cra). 360 Dr. Frances Dipper: (cla) (br). Dive Gallery/Jeffrey Jeffords (www.divegallery.com): (cb). DK Images: Frank Greenaway (cra). SeaPics.com: Masa Ushioda (bl). 361 DK Images: Jerry Young (c). Marine Wildlife: Paul Kay (tc). OSF/photo library: Doug Allan (br). SeaPics.com: Jonathan Bird (cl); Jeremy Stafford-Deitsch (cra). 362–363 FLPA: Minden Pictures/Chris Newbert. 364 Alamy Images: Blickwinkel (br); Wolfgang Pölzer (ca) (bl). DK Images: Jane Burton (cb). SeaPics.com: Doug Perrine (cla). 365 Alamy Images: Reinhard Dirscherl (tl). DK Images: Geoff Dann (clb); Colin Keates/Courtesy of the Natural History Museum, London (cr). OSF/photolibrary: Richard Herrmann (bc); Pacific Stock (br). 366 Alamy Images: Reinhard Dirscherl (tc); Sami Sarkis (c). Dive Gallery/Jeffrey Jeffords (www.divegallery. com): (crb). Marine Wildlife: Alexander Mustard (cra). SeaPics.com: Doug Perrine (bl). 367 DK Images: Dave King (bl). OSF/photolibrary: Richard Herrmann (br). SeaPics.com: Jez Tryner (tl). 368 Corbis: Staffan Widstrand (cra). DK Images: Dave King (ca). FLPA: Minden Pictures/J. H. Editorial/Cyril Ruoso (cl); Minden Pictures/Tui De Roy (crb). Oceanwide Images: Gary Bell (bc). 369 Getty Images: Image Bank/Tobias Bernhard (b). OSF/photolibrary: Olivier Grunewald (cla). 370 Getty Images: Image Bank/Pete Atkinson (t). Brook Mathews, Sydney: (br). Ilan Ben Tov, Israel: (bl). 371 FLPA: Peter Reynolds (cra); S. A. Team/ Foto Natura (tc). Getty Images: National Geographic/Bill Curtsinger (bl). SeaPics.com: Doug Perrine (br). 372–373 Harald Slauschek/ UnderwaterVisions.net. 374 Dick Bartlett: (cra). naturepl.com: Constantinos Petrinos (l). Queensland Museum, Australia (www. Qmuseum.qld.gov.au): (br). 375 Getty Images: Taxi/Gary Bell (r). SeaPics.com: Gary Bell (cla); Steve Drogin (clb). 376 Alamy Images: Pep Roig (t). Kraig Haver Photography: (bl). Still Pictures: Michael Fairchild (br). 377 FLPA: Minden Pictures/ Mike Parry (c). Adam Slavický: (bl). Scott Solar/ Amazon Reptile Center: (tl). Dr. Adam P. Summers: (br). Frank Bambang Yuwono: (tr). 378 DK Images: Ken Findlay (clb/Albatross); Chris Gomersall (clb/Curlew); Frank Greenaway/Courtesy of The National Birds of Prey Centre, Gloucestershire (clb/Sea Eagle); Rob Reichenfeld (clb/Pelican). iStockphoto.com: Hans F. Meier (cla). OSF/ photolibrary: Survival Anglia (crb). Still Pictures: Woodfall Wild Images/Everson (bc). 379 Alamy Images: PhotoStockFile/Paul Wayne Wilson (bc). OSF/photolibrary: Doug Allan (t). SeaPics.com: Richard Herrmann (br). 380 Alamy Images: Petr Svarc (cla); WorldFoto (cra). DK Images: (crb); Frank Greenaway (bl). 381 Alamy Images: Malcolm Schuyl (br); David Tipling (bl). DK Images: Steve Gorton (clb); Dave King (cr). Neil Fletcher: Tomi Muukonen (cla). Dr. Paul Hofmann: (c). 382 Alamy Images: Bryan & Cherry Alexander Photography (l). DK Images: Neil Fletcher (br). 383 Alamy Images: Kim Westerskov (bl). Neil Fletcher: Barry Hughes (cra). OSF/photolibrary: Konrad Wothe (clb). SeaPics.com: Hiroya Minakuchi (ca); Kevin Schafer (bc). 384–385 FLPA: Fritz Polking. Getty Images: National Geographic/ Paul Nicklen. 386 Alamy Images: INFOCUS Photos/Malie Rich-Griffith (bc). naturepl.com: Peter Reese (cr). OSF/photolibrary: Daniel Cox (tr) (tl). 387 Alamy Images: ImageState/Pete Oxford (bl). Neil Fletcher: Hanne & Jens Eriksen (tr). 388 Alamy Images: George McCallum Photography (ca); INFOCUS Photos/Malie RichGriffith (cb). Neil Fletcher: Hanne & Jens Eriksen (bl); Jonathan Grey (cla); Just Birds (br). 389 Alamy Images: Nature Photographers Ltd/Paul Sterry (crb). Neil Fletcher: George Reszeter (t). SeaPics. com: Doug Perrine (clb). 390 Alamy Images: Barry Bland (tr); Chris Mercer (cl). DK Images: Kim Taylor (fcl). Neil Fletcher: Just Birds (clb). SeaPics.com: Robert Shallenberger (br). 391 Alamy Images: Robert E. Barber (cr); f1 online/ Pölzer (bc). Neil Fletcher: Joe Fuhrman (tl); Mike Read (tr). SeaPics.com: Phillip Colla (br). 392 Alamy Images: Blickwinkel (b). FLPA: Minden Pictures/Tui De Roy (ca) (tr). 393 Alamy Images: WoodyStock/Ingo Schulz (cra). Neil Fletcher: Ian Montgomery (tc); Mike Read (cla). Still Pictures: Fritz Polking (br). 394 Alamy Images: Mike Lane (bl); PhotoStockFile/Paul Wayne Wilson (br). DK

Images: Cyril Laubscher (cr); Frank Greenaway/ Courtesy of the Natural History Museum, London (ca). Neil Fletcher: Barry Hughes (cla). 395 Alamy Images: Bryan & Cherry Alexander Photography (cr); R. & M. Thomas (b). SeaPics.com: Richard Herrmann (tl). Still Pictures: Steve Kaufman (cb); Tom Vezo (tr). 396 Alamy Images: George McCallum Photography (br); The Photolibrary Wales (bl). Neil Fletcher: Just Birds (cl). SeaPics.com: Scott Leslie (tr). 397 Alamy Images: Robert E. Barber (cb); Scott Camazine (tl). DK Images: Cyril Laubscher (br). Neil Fletcher: Joe Fuhrman (bl); George Reszeter (cra). 398 Alamy Images: Blickwinkel (br). DK Images: Harry Taylor/ Courtesy of the Natural History Museum, London (bc). Neil Fletcher: Dudley Edmonson (cra); Barry Hughes (tc). Getty Images: Image Bank/Roine Magnusson (c). 399 Alamy Images: Kevin Schafer (bl). DK Images: Irv Beckman (crb). OSF/ photolibrary: David Tipling (t). Still Pictures: Mark Edwards (cra). 400 Alamy Images: Brandon Cole Marine Photography (cl). DK Images: Philip Dowell (cr). Marine Wildlife: Doug Allan (bl). Still Pictures: Steven Kazlowski (clb). 400–401 OSF/ photolibrary: Mark Jones (c). 401 Alamy Images: Steven J. Kazlowski (ca). DK Images: James Stevenson & Tina Chambers/Courtesy of the National Maritime Museum, London (crb). OSF/ photolibrary: Pacific Stock (br). 402 DK Images: Jerry Young (tl). FLPA: Foto Natura/Wil Meinderts (br). Howard Hall Productions: (bl). Still Pictures: Norbert Wu (cb). 403 FLPA: Minden Pictures/Tui De Roy (bc). Getty Images: Image Bank/Joseph Van Os (tr). Brian Lockett (www.airand-space.com): (bl). Marine Wildlife: Paul Kay (cla). NOAA: Captain Budd Christman, NOAA Corps (crb). 404–405 Getty Images: National Geographic / David Doubilet. 406–407 Steve Smithson. 408 Ardea: Francois Gohier (tr). Corbis: The Mariners’ Museum (cl). FLPA: Minden Pictures/Flip Nicklin (bl). SeaPics.com: Howard Hall (bc). 409 Alamy Images: Brandon Cole Marine Photography (t); Stephen Frink Collection/ James D. Watt (b). 410–411 Marine Wildlife: Sue Flood. 412 DK Images: Frank Greenaway (tr). naturepl.com: Doc White (ca). SeaPics.com: Doug Perrine (b). 413 Alamy Images: Andre Seale (cla). FLPA: Minden Pictures/Flip Nicklin (crb). Getty Images: National Geographic/Brian Skerry (tr). SeaPics.com: John K. B. Ford/Ursus (bl). 414 FLPA: Minden Pictures/Flip Nicklin (tr). SeaPics. com: Thomas Jefferson (cl); Robert L. Pitman (br). Getty Images: Gerard Soury (bc). 415 Alamy Images: Stock Connection Blue/Tom Brakefield. 416 Marine Wildlife: Sue Flood. 417 FLPA: Minden Pictures/Michio Hoshino (ca); Minden Pictures/Flip Nicklin (cra); Minden Pictures/Norbert Wu (bc). naturepl.com: Todd Pusser (crb). Mike Scott: (cb). SeaPics.com: Phillip Colla (c). 418 FLPA: Minden Pictures/Flip Nicklin (t). Image Quest Marine: Masa Ushioda (br). SeaPics.com: Florian Graner (cl). 419 DK Images: Peter Visscher (crb). FLPA: Minden Pictures/Chris Newbert (tr). Getty Images: Photographer’s Choice/Pete Atkinson (b). Still Pictures: Douglas Faulkner (ca). 420–421 NASA: Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC. 424 Alamy Images: Bryan & Cherry Alexander Photography (cla); LOOK Die Bildagentur der Fotografen GmbH (cb). 426 Alamy Images: Jack Stephens (cla). Corbis: Lowell Georgia (cra). 427 Alamy Images: Nordicphotos/Kristjan Fridriksson (br). 428 Alamy Images: Greenshoots Communications (c); David Sanger Photography (cla). Corbis: Ralph White (bl). 430 Alamy Images: FLPA (br). 431 DK Images: David Lyons (cl). NASA: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC (ca). 432 Alamy Images: Ace Stock Ltd (bc); allOver photography (clb). DK Images: Linda Whitwam (ca). 433 Alamy Images: Nick Hanna (br). 434 Mads Eskesen. 435 Alamy Images: Mike Lane (br). Mads Eskesen: (tr) (cra). Horns Rev Havmøllepark (www.hornsrev. dk): Medvind Fotografi/Bent Sørensen (bc). Nysted Havmøllepark (www.nystedhavmoellepark.dk): (crb). Photos: E.ON: (crb/Rodsand). 437 Alamy Images: Wild Places Photography/Chris Howes (br). Corbis: Sygma/Bernard Annebicque (cr). 438 DK Images: Christopher & Sally Gable (tl); John Heseltine (br). 439 Alamy Images: Vehbi Koca (crb); Rob Rayworth (bl). NASA: Image courtesy NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./

Japan ASTER Science Team (c). 440 Corbis: (tr) (bl); Sygma/Harford Chloe (cb). NASA: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC (br). 442 Corbis: Cordaiy Photo Library Ltd/John Farmar (tr). NASA: GSFC/JPL, MISR Team (bl). Science Photo Library: Southampton Oceanography Centre/B. Murton (cla). 443 Alamy Images: Wild Places Photography/Chris Howes (cra). Corbis: (ca). 444 FLPA: Colin Monteath (br). iStockphoto.com: Patrick Roherty (bc). 445 Alamy Images: Bryan & Cherry Alexander Photography (bl). NASA: Jesse Allen, NASA Earth Observatory and the HIGP Thermal Alerts Team (cr). NOAA: Lieutenant Philip Hall, NOAA Corps (br). 446 Corbis: Yann ArthusBertrand (bl); Reuters/Supri (cla). Still Pictures: Friedrich Stark (c). 448 Alamy Images: Blickwinkel (bc); Tor Eigeland (tr). Corbis: Jonathan Blair (cl). 449 Alamy Images: Images of Africa Photobank/ Peter Williams (tr). 450 Alamy Images: Neil McAllister (br). 451 Alamy Images: Julio Etchart (cra). 452–453 Photoshot: Planet Observe. 455 iStockphoto.com: Wesley Drake (cra). OSF/ photolibrary: Michael Brooke (br). 456 Alamy Images: Danita Delimont (cla). Corbis: Ralph White (bc). NOAA: Commander Richard Behn, NOAA Corps (cl). 458 NASA: George Riggs, NASA GSFC (cra). US Fish and Wildlife Service National Image Library: Alaska Maritime National Wildlife Refuge/Kevin Bell (cla). 459 Corbis: Neil Rabinowitz (tc). 460 Alamy Images: FocusRussia (cra); Iain Masterton (cl). Corbis: Michael S.Yamashita (crb). 462–463 Corbis: Nippon News/Aflo/Newspaper/Mainichi/ Mainichi. 463 Kevin Jaako: www. jaako.com (cra/Signboard). Reuters: Yomiuri Yomiuri (cra). 464 Alamy Images: Chris Willson (br). 465 Still Pictures: Henning Christoph (cra). 467 Alamy Images: Andre Seale (br). Corbis: Douglas Faulkner (cr); Reuters/Alex De La Rosa (tr). 468 Still Pictures: Richard J. Wainscoat (cra). 469 Alamy Images: Dennis Hallinan (bc). 470–471 Getty Images: Tom Benedict. 472 OSF/photolibrary: Tammy Peluso (tr). 473 iStockphoto.com: Angela Bell (cla). SeaPics.com: Gary Bell (tc). 474 Getty Images: AFP/Tarik Tinazay. 475 Alamy Images: Nick Hanna (bl); Images&Stories (cra). Corbis: Stephen Frink (br); Jeffrey L. Rotman (bc); Lawson Wood (crb). Getty Images: Image Bank/Zac Macaulay (tr). OSF/photolibrary: David Fleetham (ca). 477 Alamy Images: Danita Delimont (cra); INTERFOTO Pressebildagentur (cb). 478 OSF/ photolibrary: Mike Hill (br). 479 iStockphoto. com: Michal Wozniak (tr). 480 Alamy Images: LOOK Die Bildagentur der Fotografen GmbH (cl); Bruce Percy (br). Corbis: Paul A. Souders (cra). 482 Alamy Images: Bryan & Cherry Alexander (cl). Still Pictures: Norbert Wu (cla) (bc). 484 Corbis: Eye Ubiquitous/C. M. Leask (cra). NOAA: Commander John Bortniak, NOAA Corps (cla). 485 Alamy Images: Blickwinkel (bl); Kim Westerskov (br). 486 Ardea: Edwin Mickleburgh. Dreamstime. com: Staphy. Back Endpapers: Getty Images: David Doubilet 487 Alamy Images: Graphic Science (tr); Steve Morgan (ca). NASA: MODIS Land Science Team (cra); Jacques Descloitres, MODIS Land Science Team (br); NASA/GSFC/LaRC/JPL, MISR Team (crb). JACKET IMAGES: Front: Dreamstime.com: Digitalbalance; Back: Dreamstime.com: Digitalbalance; Spine: Dreamstime.com: Digitalbalance. Data for the bathymetric maps in the Atlas of the Oceans chapter provided by Planetary Visions based on ETOPO2 global relief data, SRTM30 land elevation data, and the Generalised Bathymetric Chart of the Ocean. ETOPO2 published by the U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Geophysical Data Center, 2001. SRTM30 published by NASA and the National Geospatial Intelligence Agency, 2005, distributed by the U.S. Geological Survey. GEBCO One Minute Grid reproduced from the GEBCO Digital Atlas published by the British Oceanographic Data Centre on behalf of the Intergovernmental Oceanographic Commission of UNESCO and the International Hydrographic Organisation, 2003. All other images © Dorling Kindersley For further information see: www.dkimages.com

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The American Museum of Natural History in New York City is one of the largest and most respected museums in the world. Since the Museum was founded in 1869, its collections have grown to include more than 32 million specimens and artifacts relating to the natural world and human cultures. The Museum showcases its collections in the exhibit halls, and, behind the scenes, more than 200 scientists carry out cutting-edge research. It is also home to the Theodore Roosevelt Memorial, New York State’s official memorial to its thirty-third governor and the nation’s twenty-sixth president, and a tribute to Roosevelt’s enduring legacy of conservation. Approximately 5 million people from around the world visit the Museum each year. Plan a trip to the Museum, home of the world’s largest collection of dinosaur fossils, or visit online at www.amnh.org.